Ship Handling & Maneuvering : Mars
Course modified date: 10 Mar 2021
- Professor: Saliong Dionisio T
- Enrolled students: 1
Ship Handling & Maneuvering : Mercury
Course modified date: 11 June 2021
Parts of a turning circle
1. Advance - the distance traveled by the ship in the direction of the original heading measured from the point where the rudder is put hard over up to the intersection of the line at right anlge to the original track to a point where the ship has altered heading by 90 degrees.
2. Transfer - the distance the ship travels to a point when she has altered heading by 90 degrees. This is measured at right angle from the original track to the center of gravity of the ship. The center of gravity is very close to the location of the pivoting point at this instance. The transfer is about two ships lenght.
3. Tactical diameter - is the transfer when the ship has turned 180 degrees or when the heading is in the reciprocal of the original heading. Usually it is about the same as the maximum advance.
4. Drift Angle - is the angle between a line tangent to the turning circle at a point and the fore and aft line of the ship.
5. Turning circle - the circular path followed by the ship.
Effect of a turning circle on the ship's speed
Turnining circle has a slowing down or retarding down on the ship's speed because of the resistance of the water against it. The speed of the ship will slow down by 1/4 in the first 90 degrees change in heading and after turning the first 180 degrees the speed further reduces by about 1/3 to 1/2, then after these speed remains almost constant as the ship continues to turn.
Comparison of turning circle under varios condittion of the ship, speed and depth of water
1. At slow speed, the advance of the ship is from three to four ships length and will be longer at high speed..
2. A ship on light condition will have a smaller turning circle.
3. Turning radius increases as speed increase.
4. A ship timmed by the stern will have a larger turning circle because her pivoting point is further aft than when on even keel .
5. While if trimmed by the head she would have a smaller turning circle because her pivoting point is closer by the bow.
6. When a ship has a list , she will turn easily toward her high side and have a smaller turning circle on that side.
7. A ship on light condition will have a larger turning circle when going full ahead than when going slow ahead.
8. In shallow water the turning circle is larger than on deep water so that the tactical diameter maybe up to twice.
9. It is typically 60 percent greater when the draft depth ratio is 1:2 or less.
10.A twin screw can make much a smaller turning circle than single screw ship by putting one engine full ahead and the the other engine half astern.
Provision and Display of Maneuvering Information On Board Ships
Assembly Resolution A601 (15) was adopted on Nov. 19, 1987 and requires that ships should display on board the maneuvering information according to the provisions in the said resolution. The maneuvering information should be placed in the pilot card, in the wheelhouse poster and could be found in the maneuvering booklet.
Contents of the maneuvering booklet
1. The general description stating the ship's particulars and characteristics of the main engine.
2. The maneuvering characteristics in deep water describing of tests or estimate on course change performance, turning circle in deep water, accelerating turn, yaw checking, man overboard and parallel course maneuver, and lateral thruster capabilities.
3. Stopping and speed control characteristics in deep water explaining results of test made or estimated including diagrams on stopping ability deceleration and acceleration performance.
4. Maneuvering characteristics in shallow water giving the estimated turning circle at a given initial speed and time involved and the squat shown on curves.
5.Maneuvering characteristics in wind giving estimated effects of wind forces and moments eating on the ship, a course keeping limitations and drifting under water influence.
6. Maneuvering characteristics in low speed giving information on minimum rpm if the main engine with corresponding ship's speed and minimum speed at which ship can still maintain a course while having headway after stopping the engine.
7, Additional information relevant to the above topics.
Pilot Card
Is an information sheet for use by the pilot as ready reference in handling the ship during maneuvers. The information contained in the pilot card should describe the current condition of the ship with regard to her loading propulsion and maneuvering equipment and other relevant equipment.
The Wheelhouse Poster
Contains the general particulars of the ship and detailed information describing the maneuvering characteristics of the ship . the information shown on the wheelhouse poster is also found in the maneuvering booklet. It should be permanentDirectional Stability and its effect when turning and steering the ship
1. A ship is said to have a positive directional stability when founds to steady up when rudder is turned to amidship position.
2. If her rate of turn in swinging increases when the rudder is put at amidsip she has a negative directional stbility.
3. If she continues in her present rate of swing or stops swinging and proceeds on the present heading when the rudder is put amidship, she has a neutral stability.
A ship that is down by the head usually has negative directional stability. When a ship is trimmed by the stern her directional stability becomes positve and consequently has good steering stability.
Stopping Distance
Is the distance covered by the ship from the time the engine is stopped up to the place where all her headway is taken off.
Carrying way - if the time involved is also taken into account.
What is ts stopping distance? The stopping distance is one mile.
What is the carrying way? The carrying way is one mile in five minutes
The stopping distance depends on several factors such as:
1. Displacement
2. Intial speed
3.Trim
4. Form
5. Condition of the hull
6. If rudder is used
7. If engine is reversed
8. Wind and current
9. Depth of the water
Inertia Stop or Coasting Stop
When a vessel is moving ahead on acertain course and the engine is stoppedwith the rudder amidships she will continue moving forward while the headway steadily decreases until she is finally dead in the water.
Crash stop
When the engine is put astern as rapidly as possible from full ahead with the rudder amidships.
Head reach
Is the total distance traveled by the ship in the direction of the original heading.
Track reach
Is the total distance covered on the actual path until the ship is dead on the water.
What is the difference between advance and track reach because they appear to look the same? We talk of avance when we are talking of about a turning circle and we tallk about track reach when we are talking about stopping distance. The point where we start reckoning advance is when we put the rudder hard over while the point where we start track reach is when we stop the engine. In advance the engine is running while in track reach the engine is stopped although the ship is still moving by momentum.
The Accelerated Turn (Backing and Filling)
The ship could be turned in the opposite direction in an area smaller than what is needed if you were to turn her by partly making a turning circle maneuver.
1. Put the engine at half ahead and the rudder at hard starboard.
2. When the heading is almost at right angles to the original heading, put the engine at half astern or full astren if in full load condition. Put the rudder hard port to make the stern turn faster to port.
3. When the ship's head approaches the reciprocal of the original heading steady the ship by using the rudder and the engine as required.
The Williamson Turn
To bring as closely as possible back to the reciprocal of her original track for the purpose of rescueing a person who has fallen overboard in darkness, poor visibility or bad weather and the time the person who fell overboard is not known.
1. The rudder is put hard over to the same side where the person without reducing speed assuming that the accident is seen.
2. After the ship has altered course by 60 degrees from the original course, the rudder is shifted over to the other side.
3. As the ship turns round she will reach the reciprocal of the original course where she is steadied and the speed is slowed down.
It is worth mentioning however that the 60 degree alteration of the course is not always true for all types of ships and conditions.
The Single Delayed Turn
The ship continues on present course for one mile from the place where the accident happened and then put on a turning circle in a direction away from the side from where the person fall. The ship is made to go past the reciprocal course by an angle which tangent is equal to the ship's tactical diameter in miles and then steadied on that heading.
For example, if the tactical diameter is .268 mile , the equevalent angle is 15 degrees to which 180 degrees is added making the total change of course at 195 degrees.
If the ship is turned to port the equevalent angle is subtracted from the reciprocal course in order to get the heading where the ship is steadied.
The Scharnow Turn
In this maneuver, the ship will be brought back to the opposite direction of the original course and eventually back to the place whre a person has fallen overboard. The maneuver is employed when the accident is not seen.
The rudder is put hard over to one side . After the ship's heading has changed by 240 degrees the rudder is put hard over to the opposite side. When the heading is 20 degrees before the original course, the rudder is put amidship. This will bring the ship's heading to the reciprocal course then she should be steadied and slowed down.
By using the bow thruster a ship could be turned around almost on the spot. A ship could be turned to a direction opposite her orirginal course on anarea which is only about one half of her turning ciscle by employing the accelarated turn (backing and filling). By using one anchor and the engine, a ship could be turned to the opposite direction in a smaller space. In case of rescuing or searching for a person who had fallen overboard, a ship could be turned where she has passed by Williamson turn, single delayed turn or the Scharnow turn.
Navigating in a Shallow Water
A shallow water is a depth of water that is 1.5 times the deepest draft of a ship or less.
Indication of approach to Shallow Water
1. There is more vibration than normal is felt throughout the ship's hull.
2. A noticeable change in steering occurs, that is the ship does not immediately respond to the rudder movement.
Defination of Sinkage and Squat
When a ship moves through the water she undergoes a downward displacrment or a bodily sinkage resulting in an increase in mean draft. If the change is greater at either end of the ship then the resulting change in trim is called squat.
Bernoullie's Principle
When a liquid is in motion there is a drop or decrease in pressure.
Caculation of Sinkage
S = Cb x V squared
_______________
100
where S - Sinkage in meters
Cb - the ship's block coeffecient
V - the ship's speed
S = Cb x V squared
________________
30
where S - Sinkage in feet
Cb- ship.s block coefficient
V - ship's speed
The sinkage found in the above formula is multiflied by 2 in order to get the sinkage in shallow and confined water like a canal.
It should be noted that the if ship's speed is reduced by one half the ship,s snkage is reduced by one fourth.
By using the aforementioned formula you can calculate the speed to be maintained in order to have the desired underkeel clearance that is safe in shallow water.
Example
Fined the sinkage in meters in deep water for a ship with a block coefficient of .70 procceeding at speed of 12 knots.
S = 0.70 x 12 squared
__________________
100
S = 0.70 x 144
__________
100
S = 1.008 meters
Find the Sinkage in Shallow Water
S = 2 (0.70 x 12 squared)
__________________
100
S = 0.70 x 144
___________
50
S = 2.016 meters
What is the UKC of a ship with a draft of 8 meters, Cb of 0.70, traversing a water with a depth of 12 meters and the speed is 15 konts.
S = 2 (0.70 x 15 squared )
__________________
100
S = 0.70 x 225
__________
50
S = 3.15 meters
- 12 meters depth
___________________
8.85 meters
-8.00 meters draft
__________________
0.85 meters UKC
The Blokage Factor
Is the ratio between the ship's maximum underwater cross sectional area and the cross sectional area of the waterway where the ship is passing.
Example
The main draft of the ship is 6 meters and her beam is 15 meters , the submerged cross sectional area is 90 square meters, and if the width of the waterway is 25 meters and the depth of the water is is 20 meters the cross sectional area of the channel is 500 square meters The ratio therefore is 90 divided by 500 or 0.18 which is the blokage factor.
Relationship between blokag factor and Squat
The bigger the blokage factor the bigger the squat. That is why the squat in confined and shallow water becomes double than the squat in deep and open water.
Example
The main draftof a ship is 8 metersand her beam is 18 meters, if the width of the waterway is30 meters and the depth is 20 meters what is the blokage factor?
8 x 18 = 144
30 x 20 = 600
144
_____
600
0.24 is the bloking factor
Example
If the mean draft of your ship is 8 meters and her beam is 16 meters, what is the bloking factor if the width of the waterway is 30 meters and the depth is 25 meters?
8 x 16 = 128
30 x 25 = 750
128
______
750
0.1707 is the blokinf factor
Example
In Singapore strait where the depth of water is 13 meters, ship with block coefficient of 0.80 is travelling. What should be the speed in order for the ship to have a UKC of 2 meters if she has adraft of 9 meters?
13 - 9 = 4 meters
4 - 2 = 2 meters sinkage
S = 2 (Cb x V squared)
______________
100
2 = 2 (0.80 x V squared)
___________________
100
2 = 0.80 x V squared
_______________
50
V squared = 100 x 0.80
V Squared = 125
V = 11.18 is the speed of the ship
Example
In Malacca strait where the depth of water is 25 meters, a big container vessel with a draft of 18 meters and a block coefficient of 0.80 wants to proceed at its fastest safe speed maintaining an underkeel clearance of 5 meters. What speed should she use?
Depth = 25 meters
Draft = 18 meters
_____________
7 meters
UKC = 5 meters
____________
Sinkage= 2 meters
S = 2 (Cb x V squared)
________________
100
2 = 0.80 x V squared
_________________
50
100 = 0.80 x V squared
V squared = 100
_____
0.80
V squared = 125
V = 11.18 Knots
Bank Cushion and Bank Suction Effects
As the ship moves forward, the displaced water moving from astern builds up between the bow and the banks resulting in the bow being pushed away from the bank. the water rushing towards the stern between the ship and the banks drops i pressure more than on the other side of the ship on account of its faster flow . the lowest pressure drop occur near the stern of the ship so that the ship's stern moves toward the bank. Because of this since the bow is moving away fro m the bank the attraction of the stern towards the bank is made faster. The movementof the bow away from the bank is known as bank cushioneffect ad the movement of stern towards the bank is called bank suction effect.
Rounding a narrow River or Channel Bends
Where there is current the flow is fastest near the concave bank of the bend and it is slow near the convex bank. The convex bank is also known as the point. When negotiating a bend where the current is astern that is following the ship stay near the convex bank so that when the ship starts to turn the current strikes the quarter and pushes the ship's stern sideways making the stern turn at afaster rate .
If proceeding against the currnt, it is advisable to do it near the concave bank of the bend.
Inter action Between Ship's Passing close to Each other
When two ships are moving at full speed and pass close to its other , the drop in pressure of the water betwwen them combines and cause both or one of them to swing off course and cause bodily sideways movement towards or awaay from each other . This interaction effeect is more serious when the two ships are going violently on in one direction because the effect will be acting at longer time than when they are going on opposite direction.
When a ship is approaching close to a shoal her bow may suddenly move towards the shoal and then violently moves away from it . This behavior of the ship is called smelling the ground.
1. Advance - the distance traveled by the ship in the direction of the original heading measured from the point where the rudder is put hard over up to the intersection of the line at right anlge to the original track to a point where the ship has altered heading by 90 degrees.
2. Transfer - the distance the ship travels to a point when she has altered heading by 90 degrees. This is measured at right angle from the original track to the center of gravity of the ship. The center of gravity is very close to the location of the pivoting point at this instance. The transfer is about two ships lenght.
3. Tactical diameter - is the transfer when the ship has turned 180 degrees or when the heading is in the reciprocal of the original heading. Usually it is about the same as the maximum advance.
4. Drift Angle - is the angle between a line tangent to the turning circle at a point and the fore and aft line of the ship.
5. Turning circle - the circular path followed by the ship.
Effect of a turning circle on the ship's speed
Turnining circle has a slowing down or retarding down on the ship's speed because of the resistance of the water against it. The speed of the ship will slow down by 1/4 in the first 90 degrees change in heading and after turning the first 180 degrees the speed further reduces by about 1/3 to 1/2, then after these speed remains almost constant as the ship continues to turn.
Comparison of turning circle under varios condittion of the ship, speed and depth of water
1. At slow speed, the advance of the ship is from three to four ships length and will be longer at high speed..
2. A ship on light condition will have a smaller turning circle.
3. Turning radius increases as speed increase.
4. A ship timmed by the stern will have a larger turning circle because her pivoting point is further aft than when on even keel .
5. While if trimmed by the head she would have a smaller turning circle because her pivoting point is closer by the bow.
6. When a ship has a list , she will turn easily toward her high side and have a smaller turning circle on that side.
7. A ship on light condition will have a larger turning circle when going full ahead than when going slow ahead.
8. In shallow water the turning circle is larger than on deep water so that the tactical diameter maybe up to twice.
9. It is typically 60 percent greater when the draft depth ratio is 1:2 or less.
10.A twin screw can make much a smaller turning circle than single screw ship by putting one engine full ahead and the the other engine half astern.
Provision and Display of Maneuvering Information On Board Ships
Assembly Resolution A601 (15) was adopted on Nov. 19, 1987 and requires that ships should display on board the maneuvering information according to the provisions in the said resolution. The maneuvering information should be placed in the pilot card, in the wheelhouse poster and could be found in the maneuvering booklet.
Contents of the maneuvering booklet
1. The general description stating the ship's particulars and characteristics of the main engine.
2. The maneuvering characteristics in deep water describing of tests or estimate on course change performance, turning circle in deep water, accelerating turn, yaw checking, man overboard and parallel course maneuver, and lateral thruster capabilities.
3. Stopping and speed control characteristics in deep water explaining results of test made or estimated including diagrams on stopping ability deceleration and acceleration performance.
4. Maneuvering characteristics in shallow water giving the estimated turning circle at a given initial speed and time involved and the squat shown on curves.
5.Maneuvering characteristics in wind giving estimated effects of wind forces and moments eating on the ship, a course keeping limitations and drifting under water influence.
6. Maneuvering characteristics in low speed giving information on minimum rpm if the main engine with corresponding ship's speed and minimum speed at which ship can still maintain a course while having headway after stopping the engine.
7, Additional information relevant to the above topics.
Pilot Card
Is an information sheet for use by the pilot as ready reference in handling the ship during maneuvers. The information contained in the pilot card should describe the current condition of the ship with regard to her loading propulsion and maneuvering equipment and other relevant equipment.
The Wheelhouse Poster
Contains the general particulars of the ship and detailed information describing the maneuvering characteristics of the ship . the information shown on the wheelhouse poster is also found in the maneuvering booklet. It should be permanentDirectional Stability and its effect when turning and steering the ship
1. A ship is said to have a positive directional stability when founds to steady up when rudder is turned to amidship position.
2. If her rate of turn in swinging increases when the rudder is put at amidsip she has a negative directional stbility.
3. If she continues in her present rate of swing or stops swinging and proceeds on the present heading when the rudder is put amidship, she has a neutral stability.
A ship that is down by the head usually has negative directional stability. When a ship is trimmed by the stern her directional stability becomes positve and consequently has good steering stability.
Stopping Distance
Is the distance covered by the ship from the time the engine is stopped up to the place where all her headway is taken off.
Carrying way - if the time involved is also taken into account.
What is ts stopping distance? The stopping distance is one mile.
What is the carrying way? The carrying way is one mile in five minutes
The stopping distance depends on several factors such as:
1. Displacement
2. Intial speed
3.Trim
4. Form
5. Condition of the hull
6. If rudder is used
7. If engine is reversed
8. Wind and current
9. Depth of the water
Inertia Stop or Coasting Stop
When a vessel is moving ahead on acertain course and the engine is stoppedwith the rudder amidships she will continue moving forward while the headway steadily decreases until she is finally dead in the water.
Crash stop
When the engine is put astern as rapidly as possible from full ahead with the rudder amidships.
Head reach
Is the total distance traveled by the ship in the direction of the original heading.
Track reach
Is the total distance covered on the actual path until the ship is dead on the water.
What is the difference between advance and track reach because they appear to look the same? We talk of avance when we are talking of about a turning circle and we tallk about track reach when we are talking about stopping distance. The point where we start reckoning advance is when we put the rudder hard over while the point where we start track reach is when we stop the engine. In advance the engine is running while in track reach the engine is stopped although the ship is still moving by momentum.
The Accelerated Turn (Backing and Filling)
The ship could be turned in the opposite direction in an area smaller than what is needed if you were to turn her by partly making a turning circle maneuver.
1. Put the engine at half ahead and the rudder at hard starboard.
2. When the heading is almost at right angles to the original heading, put the engine at half astern or full astren if in full load condition. Put the rudder hard port to make the stern turn faster to port.
3. When the ship's head approaches the reciprocal of the original heading steady the ship by using the rudder and the engine as required.
The Williamson Turn
To bring as closely as possible back to the reciprocal of her original track for the purpose of rescueing a person who has fallen overboard in darkness, poor visibility or bad weather and the time the person who fell overboard is not known.
1. The rudder is put hard over to the same side where the person without reducing speed assuming that the accident is seen.
2. After the ship has altered course by 60 degrees from the original course, the rudder is shifted over to the other side.
3. As the ship turns round she will reach the reciprocal of the original course where she is steadied and the speed is slowed down.
It is worth mentioning however that the 60 degree alteration of the course is not always true for all types of ships and conditions.
The Single Delayed Turn
The ship continues on present course for one mile from the place where the accident happened and then put on a turning circle in a direction away from the side from where the person fall. The ship is made to go past the reciprocal course by an angle which tangent is equal to the ship's tactical diameter in miles and then steadied on that heading.
For example, if the tactical diameter is .268 mile , the equevalent angle is 15 degrees to which 180 degrees is added making the total change of course at 195 degrees.
If the ship is turned to port the equevalent angle is subtracted from the reciprocal course in order to get the heading where the ship is steadied.
The Scharnow Turn
In this maneuver, the ship will be brought back to the opposite direction of the original course and eventually back to the place whre a person has fallen overboard. The maneuver is employed when the accident is not seen.
The rudder is put hard over to one side . After the ship's heading has changed by 240 degrees the rudder is put hard over to the opposite side. When the heading is 20 degrees before the original course, the rudder is put amidship. This will bring the ship's heading to the reciprocal course then she should be steadied and slowed down.
By using the bow thruster a ship could be turned around almost on the spot. A ship could be turned to a direction opposite her orirginal course on anarea which is only about one half of her turning ciscle by employing the accelarated turn (backing and filling). By using one anchor and the engine, a ship could be turned to the opposite direction in a smaller space. In case of rescuing or searching for a person who had fallen overboard, a ship could be turned where she has passed by Williamson turn, single delayed turn or the Scharnow turn.
Navigating in a Shallow Water
A shallow water is a depth of water that is 1.5 times the deepest draft of a ship or less.
Indication of approach to Shallow Water
1. There is more vibration than normal is felt throughout the ship's hull.
2. A noticeable change in steering occurs, that is the ship does not immediately respond to the rudder movement.
Defination of Sinkage and Squat
When a ship moves through the water she undergoes a downward displacrment or a bodily sinkage resulting in an increase in mean draft. If the change is greater at either end of the ship then the resulting change in trim is called squat.
Bernoullie's Principle
When a liquid is in motion there is a drop or decrease in pressure.
Caculation of Sinkage
S = Cb x V squared
_______________
100
where S - Sinkage in meters
Cb - the ship's block coeffecient
V - the ship's speed
S = Cb x V squared
________________
30
where S - Sinkage in feet
Cb- ship.s block coefficient
V - ship's speed
The sinkage found in the above formula is multiflied by 2 in order to get the sinkage in shallow and confined water like a canal.
It should be noted that the if ship's speed is reduced by one half the ship,s snkage is reduced by one fourth.
By using the aforementioned formula you can calculate the speed to be maintained in order to have the desired underkeel clearance that is safe in shallow water.
Example
Fined the sinkage in meters in deep water for a ship with a block coefficient of .70 procceeding at speed of 12 knots.
S = 0.70 x 12 squared
__________________
100
S = 0.70 x 144
__________
100
S = 1.008 meters
Find the Sinkage in Shallow Water
S = 2 (0.70 x 12 squared)
__________________
100
S = 0.70 x 144
___________
50
S = 2.016 meters
What is the UKC of a ship with a draft of 8 meters, Cb of 0.70, traversing a water with a depth of 12 meters and the speed is 15 konts.
S = 2 (0.70 x 15 squared )
__________________
100
S = 0.70 x 225
__________
50
S = 3.15 meters
- 12 meters depth
___________________
8.85 meters
-8.00 meters draft
__________________
0.85 meters UKC
The Blokage Factor
Is the ratio between the ship's maximum underwater cross sectional area and the cross sectional area of the waterway where the ship is passing.
Example
The main draft of the ship is 6 meters and her beam is 15 meters , the submerged cross sectional area is 90 square meters, and if the width of the waterway is 25 meters and the depth of the water is is 20 meters the cross sectional area of the channel is 500 square meters The ratio therefore is 90 divided by 500 or 0.18 which is the blokage factor.
Relationship between blokag factor and Squat
The bigger the blokage factor the bigger the squat. That is why the squat in confined and shallow water becomes double than the squat in deep and open water.
Example
The main draftof a ship is 8 metersand her beam is 18 meters, if the width of the waterway is30 meters and the depth is 20 meters what is the blokage factor?
8 x 18 = 144
30 x 20 = 600
144
_____
600
0.24 is the bloking factor
Example
If the mean draft of your ship is 8 meters and her beam is 16 meters, what is the bloking factor if the width of the waterway is 30 meters and the depth is 25 meters?
8 x 16 = 128
30 x 25 = 750
128
______
750
0.1707 is the blokinf factor
Example
In Singapore strait where the depth of water is 13 meters, ship with block coefficient of 0.80 is travelling. What should be the speed in order for the ship to have a UKC of 2 meters if she has adraft of 9 meters?
13 - 9 = 4 meters
4 - 2 = 2 meters sinkage
S = 2 (Cb x V squared)
______________
100
2 = 2 (0.80 x V squared)
___________________
100
2 = 0.80 x V squared
_______________
50
V squared = 100 x 0.80
V Squared = 125
V = 11.18 is the speed of the ship
Example
In Malacca strait where the depth of water is 25 meters, a big container vessel with a draft of 18 meters and a block coefficient of 0.80 wants to proceed at its fastest safe speed maintaining an underkeel clearance of 5 meters. What speed should she use?
Depth = 25 meters
Draft = 18 meters
_____________
7 meters
UKC = 5 meters
____________
Sinkage= 2 meters
S = 2 (Cb x V squared)
________________
100
2 = 0.80 x V squared
_________________
50
100 = 0.80 x V squared
V squared = 100
_____
0.80
V squared = 125
V = 11.18 Knots
Bank Cushion and Bank Suction Effects
As the ship moves forward, the displaced water moving from astern builds up between the bow and the banks resulting in the bow being pushed away from the bank. the water rushing towards the stern between the ship and the banks drops i pressure more than on the other side of the ship on account of its faster flow . the lowest pressure drop occur near the stern of the ship so that the ship's stern moves toward the bank. Because of this since the bow is moving away fro m the bank the attraction of the stern towards the bank is made faster. The movementof the bow away from the bank is known as bank cushioneffect ad the movement of stern towards the bank is called bank suction effect.
Rounding a narrow River or Channel Bends
Where there is current the flow is fastest near the concave bank of the bend and it is slow near the convex bank. The convex bank is also known as the point. When negotiating a bend where the current is astern that is following the ship stay near the convex bank so that when the ship starts to turn the current strikes the quarter and pushes the ship's stern sideways making the stern turn at afaster rate .
If proceeding against the currnt, it is advisable to do it near the concave bank of the bend.
Inter action Between Ship's Passing close to Each other
When two ships are moving at full speed and pass close to its other , the drop in pressure of the water betwwen them combines and cause both or one of them to swing off course and cause bodily sideways movement towards or awaay from each other . This interaction effeect is more serious when the two ships are going violently on in one direction because the effect will be acting at longer time than when they are going on opposite direction.
When a ship is approaching close to a shoal her bow may suddenly move towards the shoal and then violently moves away from it . This behavior of the ship is called smelling the ground.
- Professor: Saliong Dionisio T
- Enrolled students: 16
Ship Handling & Maneuvering : Jupiter
Course modified date: 11 June 2021
Parts of a turning circle
1. Advance - the distance traveled by the ship in the direction of the original heading measured from the point where the rudder is put hard over up to the intersection of the line at right angle to the original track to a point where the ship has altered heading by 90 degrees.
2. Transfer - the distance the ship travels to a point when she has altered heading by 90 degrees. This is measured at right angle from the original track to the center of gravity of the ship. The center of gravity is very close to the location of the pivoting point at this instance. The transfer is about two ships length.
3. Tactical diameter - is the transfer when the ship has turned 180 degrees or when the heading is in the reciprocal of the original heading. Usually it is about the same as the maximum advance.
4. Drift Angle - is the angle between a line tangent to the turning circle at a point and the fore and aft line of the ship.
5. Turning circle - the circular path followed by the ship.
Effect of a turning circle on the ship's speed
Turning circle has a slowing down or retarding down on the ship's speed because of the resistance of the water against it. The speed of the ship will slow down by 1/4 in the first 90 degrees change in heading and after turning the first 180 degrees the speed further reduces by about 1/3 to 1/2, then after these speed remains almost constant as the ship continues to turn.
Comparison of turning circle under various condition of the ship, speed and depth of water
1. At slow speed, the advance of the ship is from three to four ships length and will be longer at high speed..
2. A ship on light condition will have a smaller turning circle.
3. Turning radius increases as speed increase.
4. A ship timed by the stern will have a larger turning circle because her pivoting point is further aft than when on even keel .
5. While if trimmed by the head she would have a smaller turning circle because her pivoting point is closer by the bow.
6. When a ship has a list , she will turn easily toward her high side and have a smaller turning circle on that side.
7. A ship on light condition will have a larger turning circle when going full ahead than when going slow ahead.
8. In shallow water the turning circle is larger than on deep water so that the tactical diameter maybe up to twice.
9. It is typically 60 percent greater when the draft depth ratio is 1:2 or less.
10.A twin screw can make much a smaller turning circle than single screw ship by putting one engine full ahead and the the other engine half astern.
Provision and Display of Maneuvering Information On Board Ships
Assembly Resolution A601 (15) was adopted on Nov. 19, 1987 and requires that ships should display on board the maneuvering information according to the provisions in the said resolution. The maneuvering information should be placed in the pilot card, in the wheelhouse poster and could be found in the maneuvering booklet.
Contents of the maneuvering booklet
1. The general description stating the ship's particulars and characteristics of the main engine.
2. The maneuvering characteristics in deep water describing of tests or estimate on course change performance, turning circle in deep water, accelerating turn, yaw checking, man overboard and parallel course maneuver, and lateral thruster capabilities.
3. Stopping and speed control characteristics in deep water explaining results of test made or estimated including diagrams on stopping ability deceleration and acceleration performance.
4. Maneuvering characteristics in shallow water giving the estimated turning circle at a given initial speed and time involved and the squat shown on curves.
5.Maneuvering characteristics in wind giving estimated effects of wind forces and moments eating on the ship, a course keeping limitations and drifting under water influence.
6. Maneuvering characteristics in low speed giving information on minimum rpm if the main engine with corresponding ship's speed and minimum speed at which ship can still maintain a course while having headway after stopping the engine.
7, Additional information relevant to the above topics.
Pilot Card
Is an information sheet for use by the pilot as ready reference in handling the ship during maneuvers. The information contained in the pilot card should describe the current condition of the ship with regard to her loading propulsion and maneuvering equipment and other relevant equipment.
The Wheelhouse Poster
Contains the general particulars of the ship and detailed information describing the maneuvering characteristics of the ship . the information shown on the wheelhouse poster is also found in the maneuvering booklet. It should be permanently displayed on a conspicuous place on the bulkhead on the wheelhouse.
Directional Stability and its effect when turning and steering the ship
1. A ship is said to have a positive directional stability when founds to steady up when rudder is turned to amidship position.
2. If her rate of turn in swinging increases when the rudder is put at amidsip she has a negative directional stbility.
3. If she continues in her present rate of swing or stops swinging and proceeds on the present heading when the rudder is put amidship, she has a neutral stability.
A ship that is down by the head usually has negative directional stability. When a ship is trimmed by the stern her directional stability becomes positve and consequently has good steering stability.
Stopping Distance
Is the distance covered by the ship from the time the engine is stopped up to the place where all her headway is taken off.
Carrying way - if the time involved is also taken into account.
What is ts stopping distance? The stopping distance is one mile.
What is the carrying way? The carrying way is one mile in five minutes
The stopping distance depends on several factors such as:
1. Displacement
2. Intial speed
3.Trim
4. Form
5. Condition of the hull
6. If rudder is used
7. If engine is reversed
8. Wind and current
9. Depth of the water
Inertia Stop or Coasting Stop
When a vessel is moving ahead on acertain course and the engine is stoppedwith the rudder amidships she will continue moving forward while the headway steadily decreases until she is finally dead in the water.
Crash stop
When the engine is put astern as rapidly as possible from full ahead with the rudder amidships.
Head reach
Is the total distance traveled by the ship in the direction of the original heading.
Track reach
Is the total distance carried on the actual path until the ship is dead on the water.
What is the difference between advance and track reach because they appear to look the same? We talk of avance when we are talking of about a turning circle and we tallk about track reach when we are talking about stopping distance. The point where we start reckoning advance is when we put the rudder hard over while the point where we start track reach is when we stop the engine. In advance the engine is running while in track reach the engine is stopped although the ship is still moving by momentum.
The Accelerated Turn (Backing and Filling)
The ship could be turned in the opposite direction in an area smaller than what is needed if you were to turn her by partly making a turning circle maneuver.
1. Put the engine at half ahead and the rudder at hard starboard.
2. When the heading is almost at right angles to the original heading, put the engine at half astern or full astren if in full load condition. Put the rudder hard port to make the stern turn faster to port.
3. When the ship's head approaches the reciprocal of the original heading steady the ship by using the rudder and the engine as required.
The Williamson Turn
To bring as closely as possible back to the reciprocal of her original track for the purpose of rescueing a person who has fallen overboard in darkness, poor visibility or bad weather and the time the person who fell overboard is not known.
1. The rudder is put hard over to the same side where the person without reducing speed assuming that the accident is seen.
2. After the ship has altered course by 60 degrees from the original course, the rudder is shifted over to the other side.
3. As the ship turns round she will reach the reciprocal of the original course where she is steadied and the speed is slowed down.
It is worth mentioning however that the 60 degree alteration of the course is not always true for all types of ships and conditions
The Single Delayed Turn
The ship continues on present course for one mile from the place where the accident happened and then put on a turning circle in a direction away from the side from where the person fall. The ship is made to go past the reciprocal course by an angle which tangent is equal to the ship's tactical diameter in miles and then steadied on that heading.
For example, if the tactical diameter is .268 mile , the equevalent angle is 15 degrees to which 180 degrees is added making the total change of course at 195 degrees.
If the ship is turned to port the equevalent angle is subtracted from the reciprocal course in order to get the heading where the ship is steadied.
The Scharnow Turn
In this maneuver, the ship will be brought back to the opposite direction of the original course and eventually back to the place whre a person has fallen overboard. The maneuver is employed when the accident is not seen.
The rudder is put hard over to one side . After the ship's heading has changed by 240 degrees the rudder is put hard over to the opposite side. When the heading is 20 degrees before the original course, the rudder is put amidship. This will bring the ship's heading to the reciprocal course then she should be steadied and slowed down.
By using the bow thruster a ship could be turned around almost on the spot. A ship could be turned to a direction opposite her orirginal course on anarea which is only about one half of her turning ciscle by employing the accelarated turn (backing and filling). By using one anchor and the engine, a ship could be turned to the opposite direction in a smaller space. In case of rescuing or searching for a person who had fallen overboard, a ship could be turned where she has passed by Williamson turn, single delayed turn or the Scharnow turn.
Navigating in a Shallow Water
A shallow water is a depth of water that is 1.5 times the deepest draft of a ship or less.
Indication of approach to Shallow Water
1. There is more vibration than normal is felt throughout the ship's hull.
2. A noticeable change in steering occurs, that is the ship does not immediately respond to the rudder movement.
Defination of Sinkage and Squat
When a ship moves through the water she undergoes a downward displacrment or a bodily sinkage resulting in an increase in mean draft. If the change is greater at either end of the ship then the resulting change in trim is called squat.
Bernoullie's Principle
When a liquid is in motion there is a drop or decrease in pressure.
Caculation of Sinkage
S = Cb x V squared
_______________
100
where S - Sinkage in meters
Cb - the ship's block coeffecient
V - the ship's speed
S = Cb x V squared
________________
30
where S - Sinkage in feet
Cb- ship.s block coefficient
V - ship's speed
The sinkage found in the above formula is multiflied by 2 in order to get the sinkage in shallow and confined water like a canal.
It should be noted that the if ship's speed is reduced by one half the ship,s snkage is reduced by one fourth.
By using the aforementioned formula you can calculate the speed to be maintained in order to have the desired underkeel clearance that is safe in shallow water.
Example
Fined the sinkage in meters in deep water for a ship with a block coefficient of .70 procceeding at speed of 12 knots.
S = 0.70 x 12 squared
__________________
100
S = 0.70 x 144
__________
100
S = 1.008 meters
Find the Sinkage in Shallow Water
S = 2 (0.70 x 12 squared)
__________________
100
S = 0.70 x 144
___________
50
S = 2.016 meters
What is the UKC of a ship with a draft of 8 meters, Cb of 0.70, traversing a water with a depth of 12 meters and the speed is 15 konts.
S = 2 (0.70 x 15 squared )
__________________
100
S = 0.70 x 225
__________
50
S = 3.15 meters
- 12 meters depth
___________________
8.85 meters
-8.00 meters draft
__________________
0.85 meters UKC
The Blokage Factor
Is the ratio between the ship's maximum underwater cross sectional area and the cross sectional area of the waterway where the ship is passing.
Example
The main draft of the ship is 6 meters and her beam is 15 meters , the submerged cross sectional area is 90 square meters, and if the width of the waterway is 25 meters and the depth of the water is is 20 meters the cross sectional area of the channel is 500 square meters The ratio therefore is 90 divided by 500 or 0.18 which is the blokage factor.
Relationship between blokag factor and Squat
The bigger the blokage factor the bigger the squat. That is why the squat in confined and shallow water becomes double than the squat in deep and open water.
Example
The main draftof a ship is 8 metersand her beam is 18 meters, if the width of the waterway is30 meters and the depth is 29 meters what is the blokage factor?
8 x 18 = 144
30 x 20 = 600
144
_____
600
0.24 is the bloking factor
Example
If the mean draft of your ship is 8 meters and her beam is 16 meters, what is the bloking factor if the width of the waterway is 30 meters and the depth is 25 meters?
8 x 16 = 128
30 x 25 = 750
128
______
750
0.1707 is the blokinf factor
Example
In Singapore strait where the depth of water is 13 meters, ship with block coefficient of 0.80 is travelling. What should be the speed in order for the ship to have a UKC of 2 meters if she has adraft of 9 meters?
13 - 9 = 4 meters
4 - 2 = 2 meters sinkage
S = 2 (Cb x V squared)
______________
100
2 = 2 (0.80 x V squared)
___________________
100
2 = 0.80 x V squared
_______________
50
V squared = 100 x 0.80
V Squared = 125
V = 11.18 is the speed of the ship
Example
In Malacca strait where the depth of water is 25 meters, a big container vessel with a draft of 18 meters and a block coefficient of 0.80 wants to proceed at its fastest safe speed maintaining an underkeel clearance of 5 meters. What speed should she use?
Depth = 25 meters
Draft = 18 meters
_____________
7 meters
UKC = 5 meters
____________
Sinkage= 2 meters
S = 2 (Cb x V squared)
________________
100
2 = 0.80 x V squared
_________________
50
100 = 0.80 x V squared
V squared = 100
_____
0.80
V squared = 125
V = 11.18 Knots
Bank Cushion and Bank Suction Effects
As the ship moves forward, the displaced water moving from astern builds up between the bow and the banks resulting in the bow being pushed away from the bank. the water rushing towards the stern between the ship and the banks drops i pressure more than on the other side of the ship on account of its faster flow . the lowest pressure drop occur near the stern of the ship so that the ship's stern moves toward the bank. Because of this since the bow is moving away fro m the bank the attraction of the stern towards the bank is made faster. The movementof the bow away from the bank is known as bank cushioneffect ad the movement of stern towards the bank is called bank suction effect.
Rounding a narrow River or Channel Bends
Where there is current the flow is fastest near the concave bank of the bend and it is slow near the convex bank. The convex bank is also known as the point. When negotiating a bend where the current is astern that is following the ship stay near the convex bank so that when the ship starts to turn the current strikes the quarter and pushes the ship's stern sideways making the stern turn at afaster rate .
If proceeding against the currnt, it is advisable to do it near the concave bank of the bend.
Inter action Between Ship's Passing close to Each other
When two ships are moving at full speed and pass close to its other , the drop in pressure of the water betwwen them combines and cause both or one of them to swing off course and cause bodily sideways movement towards or awaay from each other . This interaction effeect is more serious when the two ships are going violently on in one direction because the effect will be acting at longer time than when they are going on opposite direction.
When a ship is approaching close to a shoal her bow may suddenly move towards the shoal and then violently moves away from it . This behavior of the ship is called smelling the ground.
1. Advance - the distance traveled by the ship in the direction of the original heading measured from the point where the rudder is put hard over up to the intersection of the line at right angle to the original track to a point where the ship has altered heading by 90 degrees.
2. Transfer - the distance the ship travels to a point when she has altered heading by 90 degrees. This is measured at right angle from the original track to the center of gravity of the ship. The center of gravity is very close to the location of the pivoting point at this instance. The transfer is about two ships length.
3. Tactical diameter - is the transfer when the ship has turned 180 degrees or when the heading is in the reciprocal of the original heading. Usually it is about the same as the maximum advance.
4. Drift Angle - is the angle between a line tangent to the turning circle at a point and the fore and aft line of the ship.
5. Turning circle - the circular path followed by the ship.
Effect of a turning circle on the ship's speed
Turning circle has a slowing down or retarding down on the ship's speed because of the resistance of the water against it. The speed of the ship will slow down by 1/4 in the first 90 degrees change in heading and after turning the first 180 degrees the speed further reduces by about 1/3 to 1/2, then after these speed remains almost constant as the ship continues to turn.
Comparison of turning circle under various condition of the ship, speed and depth of water
1. At slow speed, the advance of the ship is from three to four ships length and will be longer at high speed..
2. A ship on light condition will have a smaller turning circle.
3. Turning radius increases as speed increase.
4. A ship timed by the stern will have a larger turning circle because her pivoting point is further aft than when on even keel .
5. While if trimmed by the head she would have a smaller turning circle because her pivoting point is closer by the bow.
6. When a ship has a list , she will turn easily toward her high side and have a smaller turning circle on that side.
7. A ship on light condition will have a larger turning circle when going full ahead than when going slow ahead.
8. In shallow water the turning circle is larger than on deep water so that the tactical diameter maybe up to twice.
9. It is typically 60 percent greater when the draft depth ratio is 1:2 or less.
10.A twin screw can make much a smaller turning circle than single screw ship by putting one engine full ahead and the the other engine half astern.
Provision and Display of Maneuvering Information On Board Ships
Assembly Resolution A601 (15) was adopted on Nov. 19, 1987 and requires that ships should display on board the maneuvering information according to the provisions in the said resolution. The maneuvering information should be placed in the pilot card, in the wheelhouse poster and could be found in the maneuvering booklet.
Contents of the maneuvering booklet
1. The general description stating the ship's particulars and characteristics of the main engine.
2. The maneuvering characteristics in deep water describing of tests or estimate on course change performance, turning circle in deep water, accelerating turn, yaw checking, man overboard and parallel course maneuver, and lateral thruster capabilities.
3. Stopping and speed control characteristics in deep water explaining results of test made or estimated including diagrams on stopping ability deceleration and acceleration performance.
4. Maneuvering characteristics in shallow water giving the estimated turning circle at a given initial speed and time involved and the squat shown on curves.
5.Maneuvering characteristics in wind giving estimated effects of wind forces and moments eating on the ship, a course keeping limitations and drifting under water influence.
6. Maneuvering characteristics in low speed giving information on minimum rpm if the main engine with corresponding ship's speed and minimum speed at which ship can still maintain a course while having headway after stopping the engine.
7, Additional information relevant to the above topics.
Pilot Card
Is an information sheet for use by the pilot as ready reference in handling the ship during maneuvers. The information contained in the pilot card should describe the current condition of the ship with regard to her loading propulsion and maneuvering equipment and other relevant equipment.
The Wheelhouse Poster
Contains the general particulars of the ship and detailed information describing the maneuvering characteristics of the ship . the information shown on the wheelhouse poster is also found in the maneuvering booklet. It should be permanently displayed on a conspicuous place on the bulkhead on the wheelhouse.
Directional Stability and its effect when turning and steering the ship
1. A ship is said to have a positive directional stability when founds to steady up when rudder is turned to amidship position.
2. If her rate of turn in swinging increases when the rudder is put at amidsip she has a negative directional stbility.
3. If she continues in her present rate of swing or stops swinging and proceeds on the present heading when the rudder is put amidship, she has a neutral stability.
A ship that is down by the head usually has negative directional stability. When a ship is trimmed by the stern her directional stability becomes positve and consequently has good steering stability.
Stopping Distance
Is the distance covered by the ship from the time the engine is stopped up to the place where all her headway is taken off.
Carrying way - if the time involved is also taken into account.
What is ts stopping distance? The stopping distance is one mile.
What is the carrying way? The carrying way is one mile in five minutes
The stopping distance depends on several factors such as:
1. Displacement
2. Intial speed
3.Trim
4. Form
5. Condition of the hull
6. If rudder is used
7. If engine is reversed
8. Wind and current
9. Depth of the water
Inertia Stop or Coasting Stop
When a vessel is moving ahead on acertain course and the engine is stoppedwith the rudder amidships she will continue moving forward while the headway steadily decreases until she is finally dead in the water.
Crash stop
When the engine is put astern as rapidly as possible from full ahead with the rudder amidships.
Head reach
Is the total distance traveled by the ship in the direction of the original heading.
Track reach
Is the total distance carried on the actual path until the ship is dead on the water.
What is the difference between advance and track reach because they appear to look the same? We talk of avance when we are talking of about a turning circle and we tallk about track reach when we are talking about stopping distance. The point where we start reckoning advance is when we put the rudder hard over while the point where we start track reach is when we stop the engine. In advance the engine is running while in track reach the engine is stopped although the ship is still moving by momentum.
The Accelerated Turn (Backing and Filling)
The ship could be turned in the opposite direction in an area smaller than what is needed if you were to turn her by partly making a turning circle maneuver.
1. Put the engine at half ahead and the rudder at hard starboard.
2. When the heading is almost at right angles to the original heading, put the engine at half astern or full astren if in full load condition. Put the rudder hard port to make the stern turn faster to port.
3. When the ship's head approaches the reciprocal of the original heading steady the ship by using the rudder and the engine as required.
The Williamson Turn
To bring as closely as possible back to the reciprocal of her original track for the purpose of rescueing a person who has fallen overboard in darkness, poor visibility or bad weather and the time the person who fell overboard is not known.
1. The rudder is put hard over to the same side where the person without reducing speed assuming that the accident is seen.
2. After the ship has altered course by 60 degrees from the original course, the rudder is shifted over to the other side.
3. As the ship turns round she will reach the reciprocal of the original course where she is steadied and the speed is slowed down.
It is worth mentioning however that the 60 degree alteration of the course is not always true for all types of ships and conditions
The Single Delayed Turn
The ship continues on present course for one mile from the place where the accident happened and then put on a turning circle in a direction away from the side from where the person fall. The ship is made to go past the reciprocal course by an angle which tangent is equal to the ship's tactical diameter in miles and then steadied on that heading.
For example, if the tactical diameter is .268 mile , the equevalent angle is 15 degrees to which 180 degrees is added making the total change of course at 195 degrees.
If the ship is turned to port the equevalent angle is subtracted from the reciprocal course in order to get the heading where the ship is steadied.
The Scharnow Turn
In this maneuver, the ship will be brought back to the opposite direction of the original course and eventually back to the place whre a person has fallen overboard. The maneuver is employed when the accident is not seen.
The rudder is put hard over to one side . After the ship's heading has changed by 240 degrees the rudder is put hard over to the opposite side. When the heading is 20 degrees before the original course, the rudder is put amidship. This will bring the ship's heading to the reciprocal course then she should be steadied and slowed down.
By using the bow thruster a ship could be turned around almost on the spot. A ship could be turned to a direction opposite her orirginal course on anarea which is only about one half of her turning ciscle by employing the accelarated turn (backing and filling). By using one anchor and the engine, a ship could be turned to the opposite direction in a smaller space. In case of rescuing or searching for a person who had fallen overboard, a ship could be turned where she has passed by Williamson turn, single delayed turn or the Scharnow turn.
Navigating in a Shallow Water
A shallow water is a depth of water that is 1.5 times the deepest draft of a ship or less.
Indication of approach to Shallow Water
1. There is more vibration than normal is felt throughout the ship's hull.
2. A noticeable change in steering occurs, that is the ship does not immediately respond to the rudder movement.
Defination of Sinkage and Squat
When a ship moves through the water she undergoes a downward displacrment or a bodily sinkage resulting in an increase in mean draft. If the change is greater at either end of the ship then the resulting change in trim is called squat.
Bernoullie's Principle
When a liquid is in motion there is a drop or decrease in pressure.
Caculation of Sinkage
S = Cb x V squared
_______________
100
where S - Sinkage in meters
Cb - the ship's block coeffecient
V - the ship's speed
S = Cb x V squared
________________
30
where S - Sinkage in feet
Cb- ship.s block coefficient
V - ship's speed
The sinkage found in the above formula is multiflied by 2 in order to get the sinkage in shallow and confined water like a canal.
It should be noted that the if ship's speed is reduced by one half the ship,s snkage is reduced by one fourth.
By using the aforementioned formula you can calculate the speed to be maintained in order to have the desired underkeel clearance that is safe in shallow water.
Example
Fined the sinkage in meters in deep water for a ship with a block coefficient of .70 procceeding at speed of 12 knots.
S = 0.70 x 12 squared
__________________
100
S = 0.70 x 144
__________
100
S = 1.008 meters
Find the Sinkage in Shallow Water
S = 2 (0.70 x 12 squared)
__________________
100
S = 0.70 x 144
___________
50
S = 2.016 meters
What is the UKC of a ship with a draft of 8 meters, Cb of 0.70, traversing a water with a depth of 12 meters and the speed is 15 konts.
S = 2 (0.70 x 15 squared )
__________________
100
S = 0.70 x 225
__________
50
S = 3.15 meters
- 12 meters depth
___________________
8.85 meters
-8.00 meters draft
__________________
0.85 meters UKC
The Blokage Factor
Is the ratio between the ship's maximum underwater cross sectional area and the cross sectional area of the waterway where the ship is passing.
Example
The main draft of the ship is 6 meters and her beam is 15 meters , the submerged cross sectional area is 90 square meters, and if the width of the waterway is 25 meters and the depth of the water is is 20 meters the cross sectional area of the channel is 500 square meters The ratio therefore is 90 divided by 500 or 0.18 which is the blokage factor.
Relationship between blokag factor and Squat
The bigger the blokage factor the bigger the squat. That is why the squat in confined and shallow water becomes double than the squat in deep and open water.
Example
The main draftof a ship is 8 metersand her beam is 18 meters, if the width of the waterway is30 meters and the depth is 29 meters what is the blokage factor?
8 x 18 = 144
30 x 20 = 600
144
_____
600
0.24 is the bloking factor
Example
If the mean draft of your ship is 8 meters and her beam is 16 meters, what is the bloking factor if the width of the waterway is 30 meters and the depth is 25 meters?
8 x 16 = 128
30 x 25 = 750
128
______
750
0.1707 is the blokinf factor
Example
In Singapore strait where the depth of water is 13 meters, ship with block coefficient of 0.80 is travelling. What should be the speed in order for the ship to have a UKC of 2 meters if she has adraft of 9 meters?
13 - 9 = 4 meters
4 - 2 = 2 meters sinkage
S = 2 (Cb x V squared)
______________
100
2 = 2 (0.80 x V squared)
___________________
100
2 = 0.80 x V squared
_______________
50
V squared = 100 x 0.80
V Squared = 125
V = 11.18 is the speed of the ship
Example
In Malacca strait where the depth of water is 25 meters, a big container vessel with a draft of 18 meters and a block coefficient of 0.80 wants to proceed at its fastest safe speed maintaining an underkeel clearance of 5 meters. What speed should she use?
Depth = 25 meters
Draft = 18 meters
_____________
7 meters
UKC = 5 meters
____________
Sinkage= 2 meters
S = 2 (Cb x V squared)
________________
100
2 = 0.80 x V squared
_________________
50
100 = 0.80 x V squared
V squared = 100
_____
0.80
V squared = 125
V = 11.18 Knots
Bank Cushion and Bank Suction Effects
As the ship moves forward, the displaced water moving from astern builds up between the bow and the banks resulting in the bow being pushed away from the bank. the water rushing towards the stern between the ship and the banks drops i pressure more than on the other side of the ship on account of its faster flow . the lowest pressure drop occur near the stern of the ship so that the ship's stern moves toward the bank. Because of this since the bow is moving away fro m the bank the attraction of the stern towards the bank is made faster. The movementof the bow away from the bank is known as bank cushioneffect ad the movement of stern towards the bank is called bank suction effect.
Rounding a narrow River or Channel Bends
Where there is current the flow is fastest near the concave bank of the bend and it is slow near the convex bank. The convex bank is also known as the point. When negotiating a bend where the current is astern that is following the ship stay near the convex bank so that when the ship starts to turn the current strikes the quarter and pushes the ship's stern sideways making the stern turn at afaster rate .
If proceeding against the currnt, it is advisable to do it near the concave bank of the bend.
Inter action Between Ship's Passing close to Each other
When two ships are moving at full speed and pass close to its other , the drop in pressure of the water betwwen them combines and cause both or one of them to swing off course and cause bodily sideways movement towards or awaay from each other . This interaction effeect is more serious when the two ships are going violently on in one direction because the effect will be acting at longer time than when they are going on opposite direction.
When a ship is approaching close to a shoal her bow may suddenly move towards the shoal and then violently moves away from it . This behavior of the ship is called smelling the ground.
- Professor: Saliong Dionisio T
- Enrolled students: 25
Ship Handling & Maneuvering : Venus
Course modified date: 11 June 2021
Parts of a turning circle
1. Advance - the distance traveled by the ship in the direction of the original heading measured from the point where the rudder is put hard over up to the intersection of the line at right angle to the original track to a point where the ship has altered heading by 90 degrees.
2. Transfer - the distance the ship travels to a point when she has altered heading by 90 degrees. This is measured at right angle from the original track to the center of gravity of the ship. The center of gravity is very close to the location of the pivoting point at this instance. The transfer is about two ships length.
3. Tactical diameter - is the transfer when the ship has turned 180 degrees or when the heading is in the reciprocal of the original heading. Usually it is about the same as the maximum advance.
4. Drift Angle - is the angle between a line tangent to the turning circle at a point and the fore and aft line of the ship.
5. Turning circle - the circular path followed by the ship.
Effect of a turning circle on the ship's speed
Turning circle has a slowing down or retarding down on the ship's speed because of the resistance of the water against it. The speed of the ship will slow down by 1/4 in the first 90 degrees change in heading and after turning the first 180 degrees the speed further reduces by about 1/3 to 1/2, then after these speed remains almost constant as the ship continues to turn.
Comparison of turning circle under various condition of the ship, speed and depth of water
1. At slow speed, the advance of the ship is from three to four ships length and will be longer at high speed..
2. A ship on light condition will have a smaller turning circle.
3. Turning radius increases as speed increase.
4. A ship timed by the stern will have a larger turning circle because her pivoting point is further aft than when on even keel .
5. While if trimmed by the head she would have a smaller turning circle because her pivoting point is closer by the bow.
6. When a ship has a list , she will turn easily toward her high side and have a smaller turning circle on that side.
7. A ship on light condition will have a larger turning circle when going full ahead than when going slow ahead.
8. In shallow water the turning circle is larger than on deep water so that the tactical diameter maybe up to twice.
9. It is typically 60 percent greater when the draft depth ratio is 1:2 or less.
10.A twin screw can make much a smaller turning circle than single screw ship by putting one engine full ahead and the the other engine half astern.
Provision and Display of Maneuvering Information On Board Ships
Assembly Resolution A601 (15) was adopted on Nov. 19, 1987 and requires that ships should display on board the maneuvering information according to the provisions in the said resolution. The maneuvering information should be placed in the pilot card, in the wheelhouse poster and could be found in the maneuvering booklet.
Contents of the maneuvering booklet
1. The general description stating the ship's particulars and characteristics of the main engine.
2. The maneuvering characteristics in deep water describing of tests or estimate on course change performance, turning circle in deep water, accelerating turn, yaw checking, man overboard and parallel course maneuver, and lateral thruster capabilities.
3. Stopping and speed control characteristics in deep water explaining results of test made or estimated including diagrams on stopping ability deceleration and acceleration performance.
4. Maneuvering characteristics in shallow water giving the estimated turning circle at a given initial speed and time involved and the squat shown on curves.
5.Maneuvering characteristics in wind giving estimated effects of wind forces and moments eating on the ship, a course keeping limitations and drifting under water influence.
6. Maneuvering characteristics in low speed giving information on minimum rpm if the main engine with corresponding ship's speed and minimum speed at which ship can still maintain a course while having headway after stopping the engine.
7, Additional information relevant to the above topics.
Pilot Card
Is an information sheet for use by the pilot as ready reference in handling the ship during maneuvers. The information contained in the pilot card should describe the current condition of the ship with regard to her loading propulsion and maneuvering equipment and other relevant equipment.
The Wheelhouse Poster
Contains the general particulars of the ship and detailed information describing the maneuvering characteristics of the ship . the information shown on the wheelhouse poster is also found in the maneuvering booklet. It should be permanently displayed on a conspicuous place on the bulkhead on the wheelhouse.Directional Stability and its effect when turning and steering the ship
1. A ship is said to have a positive directional stability when founds to steady up when rudder is turned to amidship position.
2. If her rate of turn in swinging increases when the rudder is put at amidsip she has a negative directional stbility.
3. If she continues in her present rate of swing or stops swinging and proceeds on the present heading when the rudder is put amidship, she has a neutral stability.
A ship that is down by the head usually has negative directional stability. When a ship is trimmed by the stern her directional stability becomes positve and consequently has good steering stability.
Stopping Distance
Is the distance covered by the ship from the time the engine is stopped up to the place where all her headway is taken off.
Carrying way - if the time involved is also taken into account.
What is ts stopping distance? The stopping distance is one mile.
What is the carrying way? The carrying way is one mile in five minutes
The stopping distance depends on several factors such as:
1. Displacement
2. Intial speed
3.Trim
4. Form
5. Condition of the hull
6. If rudder is used
7. If engine is reversed
8. Wind and current
9. Depth of the water
Inertia Stop or Coasting Stop
When a vessel is moving ahead on acertain course and the engine is stoppedwith the rudder amidships she will continue moving forward while the headway steadily decreases until she is finally dead in the water.
Crash stop
When the engine is put astern as rapidly as possible from full ahead with the rudder amidships.
Head reach
Is the total distance traveled by the ship in the direction of the original heading.
Track reach
Is the total distance covered on the actual path until the ship is dead on the water.
What is the difference between advance and track reach because they appear to look the same? We talk of avance when we are talking of about a turning circle and we tallk about track reach when we are talking about stopping distance. The point where we start reckoning advance is when we put the rudder hard over while the point where we start track reach is when we stop the engine. In advance the engine is running while in track reach the engine is stopped although the ship is still moving by momentum.
The Accelerated Turn (Backing and Filling)
The ship could be turned in the opposite direction in an area smaller than what is needed if you were to turn her by partly making a turning circle maneuver.
1. Put the engine at half ahead and the rudder at hard starboard.
2. When the heading is almost at right angles to the original heading, put the engine at half astern or full astren if in full load condition. Put the rudder hard port to make the stern turn faster to port.
3. When the ship's head approaches the reciprocal of the original heading steady the ship by using the rudder and the engine as required.
The Williamson Turn
To bring as closely as possible back to the reciprocal of her original track for the purpose of rescueing a person who has fallen overboard in darkness, poor visibility or bad weather and the time the person who fell overboard is not known.
1. The rudder is put hard over to the same side where the person without reducing speed assuming that the accident is seen.
2. After the ship has altered course by 60 degrees from the original course, the rudder is shifted over to the other side.
3. As the ship turns round she will reach the reciprocal of the original course where she is steadied and the speed is slowed down.
It is The Single Delayed Turn
The ship continues on present course for one mile from the place where the accident happened and then put on a turning circle in a direction away from the side from where the person fall. The ship is made to go past the reciprocal course by an angle which tangent is equal to the ship's tactical diameter in miles and then steadied on that heading.
For example, if the tactical diameter is .268 mile , the equevalent angle is 15 degrees to which 180 degrees is added making the total change of course at 195 degrees.
If the ship is turned to port the equevalent angle is subtracted from the reciprocal course in order to get the heading where the ship is steadied.
The Scharnow Turn
In this maneuver, the ship will be brought back to the opposite direction of the original course and eventually back to the place whre a person has fallen overboard. The maneuver is employed when the accident is not seen.
The rudder is put hard over to one side . After the ship's heading has changed by 240 degrees the rudder is put hard over to the opposite side. When the heading is 20 degrees before the original course, the rudder is put amidship. This will bring the ship's heading to the reciprocal course then she should be steadied and slowed down.
worth mentioning however that the 60 degree alteration of the course is not always true for all types of ships and conditions.
By using the bow thruster a ship could be turned around almost on the spot. A ship could be turned to a direction opposite her orirginal course on anarea which is only about one half of her turning ciscle by employing the accelarated turn (backing and filling). By using one anchor and the engine, a ship could be turned to the opposite direction in a smaller space. In case of rescuing or searching for a person who had fallen overboard, a ship could be turned where she has passed by Williamson turn, single delayed turn or the Scharnow turn.
Navigating in a Shallow Water
A shallow water is a depth of water that is 1.5 times the deepest draft of a ship or less.
Indication of approach to Shallow Water
1. There is more vibration than normal is felt throughout the ship's hull.
2. A noticeable change in steering occurs, that is the ship does not immediately respond to the rudder movement.
Defination of Sinkage and Squat
When a ship moves through the water she undergoes a downward displacrment or a bodily sinkage resulting in an increase in mean draft. If the change is greater at either end of the ship then the resulting change in trim is called squat.
Bernoullie's Principle
When a liquid is in motion there is a drop or decrease in pressure.
Caculation of Sinkage
S = Cb x V squared
_______________
100
where S - Sinkage in meters
Cb - the ship's block coeffecient
V - the ship's speed
S = Cb x V squared
________________
30
where S - Sinkage in feet
Cb- ship.s block coefficient
V - ship's speed
The sinkage found in the above formula is multiflied by 2 in order to get the sinkage in shallow and confined water like a canal.
It should be noted that the if ship's speed is reduced by one half the ship,s snkage is reduced by one fourth.
By using the aforementioned formula you can calculate the speed to be maintained in order to have the desired underkeel clearance that is safe in shallow water.
Example
Fined the sinkage in meters in deep water for a ship with a block coefficient of .70 procceeding at speed of 12 knots.
S = 0.70 x 12 squared
__________________
100
S = 0.70 x 144
__________
100
S = 1.008 meters
Find the Sinkage in Shallow Water
S = 2 (0.70 x 12 squared)
__________________
100
S = 0.70 x 144
___________
50
S = 2.016 meters
What is the UKC of a ship with a draft of 8 meters, Cb of 0.70, traversing a water with a depth of 12 meters and the speed is 15 konts.
S = 2 (0.70 x 15 squared )
__________________
100
S = 0.70 x 225
__________
50
S = 3.15 meters
- 12 meters depth
___________________
8.85 meters
-8.00 meters draft
__________________
0.85 meters UKC
The Blokage Factor
Is the ratio between the ship's maximum underwater cross sectional area and the cross sectional area of the waterway where the ship is passing.
Example
The main draft of the ship is 6 meters and her beam is 15 meters , the submerged cross sectional area is 90 square meters, and if the width of the waterway is 25 meters and the depth of the water is is 20 meters the cross sectional area of the channel is 500 square meters The ratio therefore is 90 divided by 500 or 0.18 which is the blokage factor.
Relationship between blokag factor and Squat
The bigger the blokage factor the bigger the squat. That is why the squat in confined and shallow water becomes double than the squat in deep and open water.
Example
The main draftof a ship is 8 metersand her beam is 18 meters, if the width of the waterway is30 meters and the depth is 20 meters what is the blokage factor?
8 x 18 = 144
30 x 20 = 600
144
_____
600
0.24 is the bloking factor
Example
If the mean draft of your ship is 8 meters and her beam is 16 meters, what is the bloking factor if the width of the waterway is 30 meters and the depth is 25 meters?
8 x 16 = 128
30 x 25 = 750
128
______
750
0.1707 is the blokinf factor
Example
In Singapore strait where the depth of water is 13 meters, ship with block coefficient of 0.80 is travelling. What should be the speed in order for the ship to have a UKC of 2 meters if she has adraft of 9 meters?
13 - 9 = 4 meters
4 - 2 = 2 meters sinkage
S = 2 (Cb x V squared)
______________
100
2 = 2 (0.80 x V squared)
___________________
100
2 = 0.80 x V squared
_______________
50
V squared = 100 x 0.80
V Squared = 125
V = 11.18 is the speed of the ship
Example
In Malacca strait where the depth of water is 25 meters, a big container vessel with a draft of 18 meters and a block coefficient of 0.80 wants to proceed at its fastest safe speed maintaining an underkeel clearance of 5 meters. What speed should she use?
Depth = 25 meters
Draft = 18 meters
_____________
7 meters
UKC = 5 meters
____________
Sinkage= 2 meters
S = 2 (Cb x V squared)
________________
100
2 = 0.80 x V squared
_________________
50
100 = 0.80 x V squared
V squared = 100
_____
0.80
V squared = 125
V = 11.18 Knots
Bank Cushion and Bank Suction Effects
As the ship moves forward, the displaced water moving from astern builds up between the bow and the banks resulting in the bow being pushed away from the bank. the water rushing towards the stern between the ship and the banks drops i pressure more than on the other side of the ship on account of its faster flow . the lowest pressure drop occur near the stern of the ship so that the ship's stern moves toward the bank. Because of this since the bow is moving away fro m the bank the attraction of the stern towards the bank is made faster. The movementof the bow away from the bank is known as bank cushioneffect ad the movement of stern towards the bank is called bank suction effect.
Rounding a narrow River or Channel Bends
Where there is current the flow is fastest near the concave bank of the bend and it is slow near the convex bank. The convex bank is also known as the point. When negotiating a bend where the current is astern that is following the ship stay near the convex bank so that when the ship starts to turn the current strikes the quarter and pushes the ship's stern sideways making the stern turn at afaster rate .
If proceeding against the currnt, it is advisable to do it near the concave bank of the bend.
Inter action Between Ship's Passing close to Each other
When two ships are moving at full speed and pass close to its other , the drop in pressure of the water betwwen them combines and cause both or one of them to swing off course and cause bodily sideways movement towards or awaay from each other . This interaction effeect is more serious when the two ships are going violently on in one direction because the effect will be acting at longer time than when they are going on opposite direction.
When a ship is approaching close to a shoal her bow may suddenly move towards the shoal and then violently moves away from it . This behavior of the ship is called smelling the ground.
1. Advance - the distance traveled by the ship in the direction of the original heading measured from the point where the rudder is put hard over up to the intersection of the line at right angle to the original track to a point where the ship has altered heading by 90 degrees.
2. Transfer - the distance the ship travels to a point when she has altered heading by 90 degrees. This is measured at right angle from the original track to the center of gravity of the ship. The center of gravity is very close to the location of the pivoting point at this instance. The transfer is about two ships length.
3. Tactical diameter - is the transfer when the ship has turned 180 degrees or when the heading is in the reciprocal of the original heading. Usually it is about the same as the maximum advance.
4. Drift Angle - is the angle between a line tangent to the turning circle at a point and the fore and aft line of the ship.
5. Turning circle - the circular path followed by the ship.
Effect of a turning circle on the ship's speed
Turning circle has a slowing down or retarding down on the ship's speed because of the resistance of the water against it. The speed of the ship will slow down by 1/4 in the first 90 degrees change in heading and after turning the first 180 degrees the speed further reduces by about 1/3 to 1/2, then after these speed remains almost constant as the ship continues to turn.
Comparison of turning circle under various condition of the ship, speed and depth of water
1. At slow speed, the advance of the ship is from three to four ships length and will be longer at high speed..
2. A ship on light condition will have a smaller turning circle.
3. Turning radius increases as speed increase.
4. A ship timed by the stern will have a larger turning circle because her pivoting point is further aft than when on even keel .
5. While if trimmed by the head she would have a smaller turning circle because her pivoting point is closer by the bow.
6. When a ship has a list , she will turn easily toward her high side and have a smaller turning circle on that side.
7. A ship on light condition will have a larger turning circle when going full ahead than when going slow ahead.
8. In shallow water the turning circle is larger than on deep water so that the tactical diameter maybe up to twice.
9. It is typically 60 percent greater when the draft depth ratio is 1:2 or less.
10.A twin screw can make much a smaller turning circle than single screw ship by putting one engine full ahead and the the other engine half astern.
Provision and Display of Maneuvering Information On Board Ships
Assembly Resolution A601 (15) was adopted on Nov. 19, 1987 and requires that ships should display on board the maneuvering information according to the provisions in the said resolution. The maneuvering information should be placed in the pilot card, in the wheelhouse poster and could be found in the maneuvering booklet.
Contents of the maneuvering booklet
1. The general description stating the ship's particulars and characteristics of the main engine.
2. The maneuvering characteristics in deep water describing of tests or estimate on course change performance, turning circle in deep water, accelerating turn, yaw checking, man overboard and parallel course maneuver, and lateral thruster capabilities.
3. Stopping and speed control characteristics in deep water explaining results of test made or estimated including diagrams on stopping ability deceleration and acceleration performance.
4. Maneuvering characteristics in shallow water giving the estimated turning circle at a given initial speed and time involved and the squat shown on curves.
5.Maneuvering characteristics in wind giving estimated effects of wind forces and moments eating on the ship, a course keeping limitations and drifting under water influence.
6. Maneuvering characteristics in low speed giving information on minimum rpm if the main engine with corresponding ship's speed and minimum speed at which ship can still maintain a course while having headway after stopping the engine.
7, Additional information relevant to the above topics.
Pilot Card
Is an information sheet for use by the pilot as ready reference in handling the ship during maneuvers. The information contained in the pilot card should describe the current condition of the ship with regard to her loading propulsion and maneuvering equipment and other relevant equipment.
The Wheelhouse Poster
Contains the general particulars of the ship and detailed information describing the maneuvering characteristics of the ship . the information shown on the wheelhouse poster is also found in the maneuvering booklet. It should be permanently displayed on a conspicuous place on the bulkhead on the wheelhouse.Directional Stability and its effect when turning and steering the ship
1. A ship is said to have a positive directional stability when founds to steady up when rudder is turned to amidship position.
2. If her rate of turn in swinging increases when the rudder is put at amidsip she has a negative directional stbility.
3. If she continues in her present rate of swing or stops swinging and proceeds on the present heading when the rudder is put amidship, she has a neutral stability.
A ship that is down by the head usually has negative directional stability. When a ship is trimmed by the stern her directional stability becomes positve and consequently has good steering stability.
Stopping Distance
Is the distance covered by the ship from the time the engine is stopped up to the place where all her headway is taken off.
Carrying way - if the time involved is also taken into account.
What is ts stopping distance? The stopping distance is one mile.
What is the carrying way? The carrying way is one mile in five minutes
The stopping distance depends on several factors such as:
1. Displacement
2. Intial speed
3.Trim
4. Form
5. Condition of the hull
6. If rudder is used
7. If engine is reversed
8. Wind and current
9. Depth of the water
Inertia Stop or Coasting Stop
When a vessel is moving ahead on acertain course and the engine is stoppedwith the rudder amidships she will continue moving forward while the headway steadily decreases until she is finally dead in the water.
Crash stop
When the engine is put astern as rapidly as possible from full ahead with the rudder amidships.
Head reach
Is the total distance traveled by the ship in the direction of the original heading.
Track reach
Is the total distance covered on the actual path until the ship is dead on the water.
What is the difference between advance and track reach because they appear to look the same? We talk of avance when we are talking of about a turning circle and we tallk about track reach when we are talking about stopping distance. The point where we start reckoning advance is when we put the rudder hard over while the point where we start track reach is when we stop the engine. In advance the engine is running while in track reach the engine is stopped although the ship is still moving by momentum.
The Accelerated Turn (Backing and Filling)
The ship could be turned in the opposite direction in an area smaller than what is needed if you were to turn her by partly making a turning circle maneuver.
1. Put the engine at half ahead and the rudder at hard starboard.
2. When the heading is almost at right angles to the original heading, put the engine at half astern or full astren if in full load condition. Put the rudder hard port to make the stern turn faster to port.
3. When the ship's head approaches the reciprocal of the original heading steady the ship by using the rudder and the engine as required.
The Williamson Turn
To bring as closely as possible back to the reciprocal of her original track for the purpose of rescueing a person who has fallen overboard in darkness, poor visibility or bad weather and the time the person who fell overboard is not known.
1. The rudder is put hard over to the same side where the person without reducing speed assuming that the accident is seen.
2. After the ship has altered course by 60 degrees from the original course, the rudder is shifted over to the other side.
3. As the ship turns round she will reach the reciprocal of the original course where she is steadied and the speed is slowed down.
It is The Single Delayed Turn
The ship continues on present course for one mile from the place where the accident happened and then put on a turning circle in a direction away from the side from where the person fall. The ship is made to go past the reciprocal course by an angle which tangent is equal to the ship's tactical diameter in miles and then steadied on that heading.
For example, if the tactical diameter is .268 mile , the equevalent angle is 15 degrees to which 180 degrees is added making the total change of course at 195 degrees.
If the ship is turned to port the equevalent angle is subtracted from the reciprocal course in order to get the heading where the ship is steadied.
The Scharnow Turn
In this maneuver, the ship will be brought back to the opposite direction of the original course and eventually back to the place whre a person has fallen overboard. The maneuver is employed when the accident is not seen.
The rudder is put hard over to one side . After the ship's heading has changed by 240 degrees the rudder is put hard over to the opposite side. When the heading is 20 degrees before the original course, the rudder is put amidship. This will bring the ship's heading to the reciprocal course then she should be steadied and slowed down.
worth mentioning however that the 60 degree alteration of the course is not always true for all types of ships and conditions.
By using the bow thruster a ship could be turned around almost on the spot. A ship could be turned to a direction opposite her orirginal course on anarea which is only about one half of her turning ciscle by employing the accelarated turn (backing and filling). By using one anchor and the engine, a ship could be turned to the opposite direction in a smaller space. In case of rescuing or searching for a person who had fallen overboard, a ship could be turned where she has passed by Williamson turn, single delayed turn or the Scharnow turn.
Navigating in a Shallow Water
A shallow water is a depth of water that is 1.5 times the deepest draft of a ship or less.
Indication of approach to Shallow Water
1. There is more vibration than normal is felt throughout the ship's hull.
2. A noticeable change in steering occurs, that is the ship does not immediately respond to the rudder movement.
Defination of Sinkage and Squat
When a ship moves through the water she undergoes a downward displacrment or a bodily sinkage resulting in an increase in mean draft. If the change is greater at either end of the ship then the resulting change in trim is called squat.
Bernoullie's Principle
When a liquid is in motion there is a drop or decrease in pressure.
Caculation of Sinkage
S = Cb x V squared
_______________
100
where S - Sinkage in meters
Cb - the ship's block coeffecient
V - the ship's speed
S = Cb x V squared
________________
30
where S - Sinkage in feet
Cb- ship.s block coefficient
V - ship's speed
The sinkage found in the above formula is multiflied by 2 in order to get the sinkage in shallow and confined water like a canal.
It should be noted that the if ship's speed is reduced by one half the ship,s snkage is reduced by one fourth.
By using the aforementioned formula you can calculate the speed to be maintained in order to have the desired underkeel clearance that is safe in shallow water.
Example
Fined the sinkage in meters in deep water for a ship with a block coefficient of .70 procceeding at speed of 12 knots.
S = 0.70 x 12 squared
__________________
100
S = 0.70 x 144
__________
100
S = 1.008 meters
Find the Sinkage in Shallow Water
S = 2 (0.70 x 12 squared)
__________________
100
S = 0.70 x 144
___________
50
S = 2.016 meters
What is the UKC of a ship with a draft of 8 meters, Cb of 0.70, traversing a water with a depth of 12 meters and the speed is 15 konts.
S = 2 (0.70 x 15 squared )
__________________
100
S = 0.70 x 225
__________
50
S = 3.15 meters
- 12 meters depth
___________________
8.85 meters
-8.00 meters draft
__________________
0.85 meters UKC
The Blokage Factor
Is the ratio between the ship's maximum underwater cross sectional area and the cross sectional area of the waterway where the ship is passing.
Example
The main draft of the ship is 6 meters and her beam is 15 meters , the submerged cross sectional area is 90 square meters, and if the width of the waterway is 25 meters and the depth of the water is is 20 meters the cross sectional area of the channel is 500 square meters The ratio therefore is 90 divided by 500 or 0.18 which is the blokage factor.
Relationship between blokag factor and Squat
The bigger the blokage factor the bigger the squat. That is why the squat in confined and shallow water becomes double than the squat in deep and open water.
Example
The main draftof a ship is 8 metersand her beam is 18 meters, if the width of the waterway is30 meters and the depth is 20 meters what is the blokage factor?
8 x 18 = 144
30 x 20 = 600
144
_____
600
0.24 is the bloking factor
Example
If the mean draft of your ship is 8 meters and her beam is 16 meters, what is the bloking factor if the width of the waterway is 30 meters and the depth is 25 meters?
8 x 16 = 128
30 x 25 = 750
128
______
750
0.1707 is the blokinf factor
Example
In Singapore strait where the depth of water is 13 meters, ship with block coefficient of 0.80 is travelling. What should be the speed in order for the ship to have a UKC of 2 meters if she has adraft of 9 meters?
13 - 9 = 4 meters
4 - 2 = 2 meters sinkage
S = 2 (Cb x V squared)
______________
100
2 = 2 (0.80 x V squared)
___________________
100
2 = 0.80 x V squared
_______________
50
V squared = 100 x 0.80
V Squared = 125
V = 11.18 is the speed of the ship
Example
In Malacca strait where the depth of water is 25 meters, a big container vessel with a draft of 18 meters and a block coefficient of 0.80 wants to proceed at its fastest safe speed maintaining an underkeel clearance of 5 meters. What speed should she use?
Depth = 25 meters
Draft = 18 meters
_____________
7 meters
UKC = 5 meters
____________
Sinkage= 2 meters
S = 2 (Cb x V squared)
________________
100
2 = 0.80 x V squared
_________________
50
100 = 0.80 x V squared
V squared = 100
_____
0.80
V squared = 125
V = 11.18 Knots
Bank Cushion and Bank Suction Effects
As the ship moves forward, the displaced water moving from astern builds up between the bow and the banks resulting in the bow being pushed away from the bank. the water rushing towards the stern between the ship and the banks drops i pressure more than on the other side of the ship on account of its faster flow . the lowest pressure drop occur near the stern of the ship so that the ship's stern moves toward the bank. Because of this since the bow is moving away fro m the bank the attraction of the stern towards the bank is made faster. The movementof the bow away from the bank is known as bank cushioneffect ad the movement of stern towards the bank is called bank suction effect.
Rounding a narrow River or Channel Bends
Where there is current the flow is fastest near the concave bank of the bend and it is slow near the convex bank. The convex bank is also known as the point. When negotiating a bend where the current is astern that is following the ship stay near the convex bank so that when the ship starts to turn the current strikes the quarter and pushes the ship's stern sideways making the stern turn at afaster rate .
If proceeding against the currnt, it is advisable to do it near the concave bank of the bend.
Inter action Between Ship's Passing close to Each other
When two ships are moving at full speed and pass close to its other , the drop in pressure of the water betwwen them combines and cause both or one of them to swing off course and cause bodily sideways movement towards or awaay from each other . This interaction effeect is more serious when the two ships are going violently on in one direction because the effect will be acting at longer time than when they are going on opposite direction.
When a ship is approaching close to a shoal her bow may suddenly move towards the shoal and then violently moves away from it . This behavior of the ship is called smelling the ground.
- Professor: Saliong Dionisio T
- Enrolled students: 26
Ship Handling & Maneuvering : Saturn
Course modified date: 16 June 2021
Parts of a turning circle
1. Advance - the distance traveled by the ship in the direction of the original heading measured from the point where the rudder is put hard over up to the intersection of the line at right angle to the original track to a point where the ship has altered heading by 90 degrees.
2. Transfer - the distance the ship travels to a point when she has altered heading by 90 degrees. This is measured at right angle from the original track to the center of gravity of the ship. The center of gravity is very close to the location of the pivoting point at this instance. The transfer is about two ships length.
3. Tactical diameter - is the transfer when the ship has turned 180 degrees or when the heading is in the reciprocal of the original heading. Usually it is about the same as the maximum advance.
4. Drift Angle - is the angle between a line tangent to the turning circle at a point and the fore and aft line of the ship.
5. Turning circle - the circular path followed by the ship.
Effect of a turning circle on the ship's speed
Turning circle has a slowing down or retarding down on the ship's speed because of the resistance of the water against it. The speed of the ship will slow down by 1/4 in the first 90 degrees change in heading and after turning the first 180 degrees the speed further reduces by about 1/3 to 1/2, then after these speed remains almost constant as the ship continues to turn.
Comparison of turning circle under various condition of the ship, speed and depth of water
1. At slow speed, the advance of the ship is from three to four ships length and will be longer at high speed..
2. A ship on light condition will have a smaller turning circle.
3. Turning radius increases as speed increase.
4. A ship timed by the stern will have a larger turning circle because her pivoting point is further aft than when on even keel .
5. While if trimmed by the head she would have a smaller turning circle because her pivoting point is closer by the bow.
6. When a ship has a list , she will turn easily toward her high side and have a smaller turning circle on that side.
7. A ship on light condition will have a larger turning circle when going full ahead than when going slow ahead.
8. In shallow water the turning circle is larger than on deep water so that the tactical diameter maybe up to twice.
9. It is typically 60 percent greater when the draft depth ratio is 1:2 or less.
10.A twin screw can make much a smaller turning circle than single screw ship by putting one engine full ahead and the the other engine half astern.
Provision and Display of Maneuvering Information On Board Ships
Assembly Resolution A601 (15) was adopted on Nov. 19, 1987 and requires that ships should display on board the maneuvering information according to the provisions in the said resolution. The maneuvering information should be placed in the pilot card, in the wheelhouse poster and could be found in the maneuvering booklet.
Contents of the maneuvering booklet
1. The general description stating the ship's particulars and characteristics of the main engine.
2. The maneuvering characteristics in deep water describing of tests or estimate on course change performance, turning circle in deep water, accelerating turn, yaw checking, man overboard and parallel course maneuver, and lateral thruster capabilities.
3. Stopping and speed control characteristics in deep water explaining results of test made or estimated including diagrams on stopping ability deceleration and acceleration performance.
4. Maneuvering characteristics in shallow water giving the estimated turning circle at a given initial speed and time involved and the squat shown on curves.
5.Maneuvering characteristics in wind giving estimated effects of wind forces and moments eating on the ship, a course keeping limitations and drifting under water influence.
6. Maneuvering characteristics in low speed giving information on minimum rpm if the main engine with corresponding ship's speed and minimum speed at which ship can still maintain a course while having headway after stopping the engine.
7, Additional information relevant to the above topics.
Pilot Card
Is an information sheet for use by the pilot as ready reference in handling the ship during maneuvers. The information contained in the pilot card should describe the current condition of the ship with regard to her loading propulsion and maneuvering equipment and other relevant equipment.
The Wheelhouse Poster
Contains the general particulars of the ship and detailed information describing the maneuvering characteristics of the ship . the information shown on the wheelhouse poster is also found in the maneuvering booklet. It should be permanently displayed on a conspicuous place on the bulkhead on the wheelhouse.Directional Stability and its effect when turning and steering the ship
1. A ship is said to have a positive directional stability when founds to steady up when rudder is turned to amidship position.
2. If her rate of turn in swinging increases when the rudder is put at amidsip she has a negative directional stbility.
3. If she continues in her present rate of swing or stops swinging and proceeds on the present heading when the rudder is put amidship, she has a neutral stability.
A ship that is down by the head usually has negative directional stability. When a ship is trimmed by the stern her directional stability becomes positve and consequently has good steering stability.
Stopping Distance
Is the distance covered by the ship from the time the engine is stopped up to the place where all her headway is taken off.
Carrying way - if the time involved is also taken into account.
What is ts stopping distance? The stopping distance is one mile.
What is the carrying way? The carrying way is one mile in five minutes
The stopping distance depends on several factors such as:
1. Displacement
2. Intial speed
3.Trim
4. Form
5. Condition of the hull
6. If rudder is used
7. If engine is reversed
8. Wind and current
9. Depth of the water
Inertia Stop or Coasting Stop
When a vessel is moving ahead on acertain course and the engine is stoppedwith the rudder amidships she will continue moving forward while the headway steadily decreases until she is finally dead in the water.
Crash stop
When the engine is put astern as rapidly as possible from full ahead with the rudder amidships.
Head reach
Is the total distance traveled by the ship in the direction of the original heading.
Track reach
Is the total distance covered on the actual path until the ship is deaed on the water.
What is the difference between advance and track reach because they appear to look the same? We talk of avance when we are talking of about a turning circle and we tallk about track reach when we are talking about stopping distance. The point where we start reckoning advance is when we put the rudder hard over while the point where we start track reach is when we stop the engine. In advance the engine is running while in track reach the engine is stopped although the ship is still moving by momentum.
The Accelerated Turn (Backing and Filling)
The ship could be turned in the opposite direction in an area smaller than what is needed if you were to turn her by partly making a turning circle maneuver.
1. Put the engine at half ahead and the rudder at hard starboard.
2. When the heading is almost at right angles to the original heading, put the engine at half astern or full astren if in full load condition. Put the rudder hard port to make the stern turn faster to port.
3. When the ship's head approaches the reciprocal of the original heading steady the ship by using the rudder and the engine as required.
The Williamson Turn
To bring as closely as possible back to the reciprocal of her original track for the purpose of rescueing a person who has fallen overboard in darkness, poor visibility or bad weather and the time the person who fell overboard is not known.
1. The rudder is put hard over to the same side where the person without reducing speed assuming that the accident is seen.
2. After the ship has altered course by 60 degrees from the original course, the rudder is shifted over to the other side.
3. As the ship turns round she will reach the reciprocal of the original course where she is steadied and the speed is slowed down.
It is worth mentioning however that the 60 degree alteration of the course is not always true for all types of ships and conditions.
The Single Delayed Turn
The ship continues on present course for one mile from the place where the accident happened and then put on a turning circle in a direction away from the side from where the person fall. The ship is made to go past the reciprocal course by an angle which tangent is equal to the ship's tactical diameter in miles and then steadied on that heading.
For example, if the tactical diameter is .268 mile , the equevalent angle is 15 degrees to which 180 degrees is added making the total change of course at 195 degrees.
If the ship is turned to port the equevalent angle is subtracted from the reciprocal course in order to get the heading where the ship is steadied.
The Scharnow Turn
In this maneuver, the ship will be brought back to the opposite direction of the original course and eventually back to the place whre a person has fallen overboard. The maneuver is employed when the accident is not seen.
The rudder is put hard over to one side . After the ship's heading has changed by 240 degrees the rudder is put hard over to the opposite side. When the heading is 20 degrees before the original course, the rudder is put amidship. This will bring the ship's heading to the reciprocal course then she should be steadied and slowed down.
By using the bow thruster a ship could be turned around almost on the spot. A ship could be turned to a direction opposite her orirginal course on anarea which is only about one half of her turning ciscle by employing the accelarated turn (backing and filling). By using one anchor and the engine, a ship could be turned to the opposite direction in a smaller space. In case of rescuing or searching for a person who had fallen overboard, a ship could be turned where she has passed by Williamson turn, single delayed turn or the Scharnow turn.
Navigating in a Shallow Water
A shallow water is a depth of water that is 1.5 times the deepest draft of a ship or less.
Indication of approach to Shallow Water
1. There is more vibration than normal is felt throughout the ship's hull.
2. A noticeable change in steering occurs, that is the ship does not immediately respond to the rudder movement.
Defination of Sinkage and Squat
When a ship moves through the water she undergoes a downward displacrment or a bodily sinkage resulting in an increase in mean draft. If the change is greater at either end of the ship then the resulting change in trim is called squat.
Bernoullie's Principle
When a liquid is in motion there is a drop or decrease in pressure.
Caculation of Sinkage
S = Cb x V squared
_______________
100
where S - Sinkage in meters
Cb - the ship's block coeffecient
V - the ship's speed
S = Cb x V squared
________________
30
where S - Sinkage in feet
Cb- ship.s block coefficient
V - ship's speed
The sinkage found in the above formula is multiflied by 2 in order to get the sinkage in shallow and confined water like a canal.
It should be noted that the if ship's speed is reduced by one half the ship,s snkage is reduced by one fourth.
By using the aforementioned formula you can calculate the speed to be maintained in order to have the desired underkeel clearance that is safe in shallow water.
Example
Fined the sinkage in meters in deep water for a ship with a block coefficient of .70 procceeding at speed of 12 knots.
S = 0.70 x 12 squared
__________________
100
S = 0.70 x 144
__________
100
S = 1.008 meters
Find the Sinkage in Shallow Water
S = 2 (0.70 x 12 squared)
__________________
100
S = 0.70 x 144
___________
50
S = 2.016 meters
What is the UKC of a ship with a draft of 8 meters, Cb of 0.70, traversing a water with a depth of 12 meters and the speed is 15 konts.
S = 2 (0.70 x 15 squared )
__________________
100
S = 0.70 x 225
__________
50
S = 3.15 meters
- 12 meters depth
___________________
8.85 meters
-8.00 meters draft
__________________
0.85 meters UKC
The Blokage Factor
Is the ratio between the ship's maximum underwater cross sectional area and the cross sectional area of the waterway where the ship is passing.
Example
The main draft of the ship is 6 meters and her beam is 15 meters , the submerged cross sectional area is 90 square meters, and if the width of the waterway is 25 meters and the depth of the water is is 20 meters the cross sectional area of the channel is 500 square meters The ratio therefore is 90 divided by 500 or 0.18 which is the blokage factor.
Relationship between blokag factor and Squat
The bigger the blokage factor the bigger the squat. That is why the squat in confined and shallow water becomes double than the squat in deep and open water.
Example
The main draftof a ship is 8 metersand her beam is 18 meters, if the width of the waterway is30 meters and the depth is 20 meters what is the blokage factor?
8 x 18 = 144
30 x 20 = 600
144
_____
600
0.24 is the bloking factor
Example
If the mean draft of your ship is 8 meters and her beam is 16 meters, what is the bloking factor if the width of the waterway is 30 meters and the depth is 25 meters?
8 x 16 = 128
30 x 25 = 750
128
______
750
0.1707 is the blokinf factor
Example
In Singapore strait where the depth of water is 13 meters, ship with block coefficient of 0.80 is travelling. What should be the speed in order for the ship to have a UKC of 2 meters if she has adraft of 9 meters?
13 - 9 = 4 meters
4 - 2 = 2 meters sinkage
S = 2 (Cb x V squared)
______________
100
2 = 2 (0.80 x V squared)
___________________
100
2 = 0.80 x V squared
_______________
50
V squared = 100 x 0.80
V Squared = 125
V = 11.18 is the speed of the ship
Example
In Malacca strait where the depth of water is 25 meters, a big container vessel with a draft of 18 meters and a block coefficient of 0.80 wants to proceed at its fastest safe speed maintaining an underkeel clearance of 5 meters. What speed should she use?
Depth = 25 meters
Draft = 18 meters
_____________
7 meters
UKC = 5 meters
____________
Sinkage= 2 meters
S = 2 (Cb x V squared)
________________
100
2 = 0.80 x V squared
_________________
50
100 = 0.80 x V squared
V squared = 100
_____
0.80
V squared = 125
V = 11.18 Knots
Bank Cushion and Bank Suction Effects
As the ship moves forward, the displaced water moving from astern builds up between the bow and the banks resulting in the bow being pushed away from the bank. the water rushing towards the stern between the ship and the banks drops i pressure more than on the other side of the ship on account of its faster flow . the lowest pressure drop occur near the stern of the ship so that the ship's stern moves toward the bank. Because of this since the bow is moving away fro m the bank the attraction of the stern towards the bank is made faster. The movementof the bow away from the bank is known as bank cushioneffect ad the movement of stern towards the bank is called bank suction effect.
Rounding a narrow River or Channel Bends
Where there is current the flow is fastest near the concave bank of the bend and it is slow near the convex bank. The convex bank is also known as the point. When negotiating a bend where the current is astern that is following the ship stay near the convex bank so that when the ship starts to turn the current strikes the quarter and pushes the ship's stern sideways making the stern turn at afaster rate .
If proceeding against the currnt, it is advisable to do it near the concave bank of the bend.
Inter action Between Ship's Passing close to Each other
When two ships are moving at full speed and pass close to its other , the drop in pressure of the water betwwen them combines and cause both or one of them to swing off course and cause bodily sideways movement towards or awaay from each other . This interaction effeect is more serious when the two ships are going violently on in one direction because the effect will be acting at longer time than when they are going on opposite direction.
When a ship is approaching close to a shoal her bow may suddenly move towards the shoal and then violently moves away from it . This behavior of the ship is called smelling the ground.
1. Advance - the distance traveled by the ship in the direction of the original heading measured from the point where the rudder is put hard over up to the intersection of the line at right angle to the original track to a point where the ship has altered heading by 90 degrees.
2. Transfer - the distance the ship travels to a point when she has altered heading by 90 degrees. This is measured at right angle from the original track to the center of gravity of the ship. The center of gravity is very close to the location of the pivoting point at this instance. The transfer is about two ships length.
3. Tactical diameter - is the transfer when the ship has turned 180 degrees or when the heading is in the reciprocal of the original heading. Usually it is about the same as the maximum advance.
4. Drift Angle - is the angle between a line tangent to the turning circle at a point and the fore and aft line of the ship.
5. Turning circle - the circular path followed by the ship.
Effect of a turning circle on the ship's speed
Turning circle has a slowing down or retarding down on the ship's speed because of the resistance of the water against it. The speed of the ship will slow down by 1/4 in the first 90 degrees change in heading and after turning the first 180 degrees the speed further reduces by about 1/3 to 1/2, then after these speed remains almost constant as the ship continues to turn.
Comparison of turning circle under various condition of the ship, speed and depth of water
1. At slow speed, the advance of the ship is from three to four ships length and will be longer at high speed..
2. A ship on light condition will have a smaller turning circle.
3. Turning radius increases as speed increase.
4. A ship timed by the stern will have a larger turning circle because her pivoting point is further aft than when on even keel .
5. While if trimmed by the head she would have a smaller turning circle because her pivoting point is closer by the bow.
6. When a ship has a list , she will turn easily toward her high side and have a smaller turning circle on that side.
7. A ship on light condition will have a larger turning circle when going full ahead than when going slow ahead.
8. In shallow water the turning circle is larger than on deep water so that the tactical diameter maybe up to twice.
9. It is typically 60 percent greater when the draft depth ratio is 1:2 or less.
10.A twin screw can make much a smaller turning circle than single screw ship by putting one engine full ahead and the the other engine half astern.
Provision and Display of Maneuvering Information On Board Ships
Assembly Resolution A601 (15) was adopted on Nov. 19, 1987 and requires that ships should display on board the maneuvering information according to the provisions in the said resolution. The maneuvering information should be placed in the pilot card, in the wheelhouse poster and could be found in the maneuvering booklet.
Contents of the maneuvering booklet
1. The general description stating the ship's particulars and characteristics of the main engine.
2. The maneuvering characteristics in deep water describing of tests or estimate on course change performance, turning circle in deep water, accelerating turn, yaw checking, man overboard and parallel course maneuver, and lateral thruster capabilities.
3. Stopping and speed control characteristics in deep water explaining results of test made or estimated including diagrams on stopping ability deceleration and acceleration performance.
4. Maneuvering characteristics in shallow water giving the estimated turning circle at a given initial speed and time involved and the squat shown on curves.
5.Maneuvering characteristics in wind giving estimated effects of wind forces and moments eating on the ship, a course keeping limitations and drifting under water influence.
6. Maneuvering characteristics in low speed giving information on minimum rpm if the main engine with corresponding ship's speed and minimum speed at which ship can still maintain a course while having headway after stopping the engine.
7, Additional information relevant to the above topics.
Pilot Card
Is an information sheet for use by the pilot as ready reference in handling the ship during maneuvers. The information contained in the pilot card should describe the current condition of the ship with regard to her loading propulsion and maneuvering equipment and other relevant equipment.
The Wheelhouse Poster
Contains the general particulars of the ship and detailed information describing the maneuvering characteristics of the ship . the information shown on the wheelhouse poster is also found in the maneuvering booklet. It should be permanently displayed on a conspicuous place on the bulkhead on the wheelhouse.Directional Stability and its effect when turning and steering the ship
1. A ship is said to have a positive directional stability when founds to steady up when rudder is turned to amidship position.
2. If her rate of turn in swinging increases when the rudder is put at amidsip she has a negative directional stbility.
3. If she continues in her present rate of swing or stops swinging and proceeds on the present heading when the rudder is put amidship, she has a neutral stability.
A ship that is down by the head usually has negative directional stability. When a ship is trimmed by the stern her directional stability becomes positve and consequently has good steering stability.
Stopping Distance
Is the distance covered by the ship from the time the engine is stopped up to the place where all her headway is taken off.
Carrying way - if the time involved is also taken into account.
What is ts stopping distance? The stopping distance is one mile.
What is the carrying way? The carrying way is one mile in five minutes
The stopping distance depends on several factors such as:
1. Displacement
2. Intial speed
3.Trim
4. Form
5. Condition of the hull
6. If rudder is used
7. If engine is reversed
8. Wind and current
9. Depth of the water
Inertia Stop or Coasting Stop
When a vessel is moving ahead on acertain course and the engine is stoppedwith the rudder amidships she will continue moving forward while the headway steadily decreases until she is finally dead in the water.
Crash stop
When the engine is put astern as rapidly as possible from full ahead with the rudder amidships.
Head reach
Is the total distance traveled by the ship in the direction of the original heading.
Track reach
Is the total distance covered on the actual path until the ship is deaed on the water.
What is the difference between advance and track reach because they appear to look the same? We talk of avance when we are talking of about a turning circle and we tallk about track reach when we are talking about stopping distance. The point where we start reckoning advance is when we put the rudder hard over while the point where we start track reach is when we stop the engine. In advance the engine is running while in track reach the engine is stopped although the ship is still moving by momentum.
The Accelerated Turn (Backing and Filling)
The ship could be turned in the opposite direction in an area smaller than what is needed if you were to turn her by partly making a turning circle maneuver.
1. Put the engine at half ahead and the rudder at hard starboard.
2. When the heading is almost at right angles to the original heading, put the engine at half astern or full astren if in full load condition. Put the rudder hard port to make the stern turn faster to port.
3. When the ship's head approaches the reciprocal of the original heading steady the ship by using the rudder and the engine as required.
The Williamson Turn
To bring as closely as possible back to the reciprocal of her original track for the purpose of rescueing a person who has fallen overboard in darkness, poor visibility or bad weather and the time the person who fell overboard is not known.
1. The rudder is put hard over to the same side where the person without reducing speed assuming that the accident is seen.
2. After the ship has altered course by 60 degrees from the original course, the rudder is shifted over to the other side.
3. As the ship turns round she will reach the reciprocal of the original course where she is steadied and the speed is slowed down.
It is worth mentioning however that the 60 degree alteration of the course is not always true for all types of ships and conditions.
The Single Delayed Turn
The ship continues on present course for one mile from the place where the accident happened and then put on a turning circle in a direction away from the side from where the person fall. The ship is made to go past the reciprocal course by an angle which tangent is equal to the ship's tactical diameter in miles and then steadied on that heading.
For example, if the tactical diameter is .268 mile , the equevalent angle is 15 degrees to which 180 degrees is added making the total change of course at 195 degrees.
If the ship is turned to port the equevalent angle is subtracted from the reciprocal course in order to get the heading where the ship is steadied.
The Scharnow Turn
In this maneuver, the ship will be brought back to the opposite direction of the original course and eventually back to the place whre a person has fallen overboard. The maneuver is employed when the accident is not seen.
The rudder is put hard over to one side . After the ship's heading has changed by 240 degrees the rudder is put hard over to the opposite side. When the heading is 20 degrees before the original course, the rudder is put amidship. This will bring the ship's heading to the reciprocal course then she should be steadied and slowed down.
By using the bow thruster a ship could be turned around almost on the spot. A ship could be turned to a direction opposite her orirginal course on anarea which is only about one half of her turning ciscle by employing the accelarated turn (backing and filling). By using one anchor and the engine, a ship could be turned to the opposite direction in a smaller space. In case of rescuing or searching for a person who had fallen overboard, a ship could be turned where she has passed by Williamson turn, single delayed turn or the Scharnow turn.
Navigating in a Shallow Water
A shallow water is a depth of water that is 1.5 times the deepest draft of a ship or less.
Indication of approach to Shallow Water
1. There is more vibration than normal is felt throughout the ship's hull.
2. A noticeable change in steering occurs, that is the ship does not immediately respond to the rudder movement.
Defination of Sinkage and Squat
When a ship moves through the water she undergoes a downward displacrment or a bodily sinkage resulting in an increase in mean draft. If the change is greater at either end of the ship then the resulting change in trim is called squat.
Bernoullie's Principle
When a liquid is in motion there is a drop or decrease in pressure.
Caculation of Sinkage
S = Cb x V squared
_______________
100
where S - Sinkage in meters
Cb - the ship's block coeffecient
V - the ship's speed
S = Cb x V squared
________________
30
where S - Sinkage in feet
Cb- ship.s block coefficient
V - ship's speed
The sinkage found in the above formula is multiflied by 2 in order to get the sinkage in shallow and confined water like a canal.
It should be noted that the if ship's speed is reduced by one half the ship,s snkage is reduced by one fourth.
By using the aforementioned formula you can calculate the speed to be maintained in order to have the desired underkeel clearance that is safe in shallow water.
Example
Fined the sinkage in meters in deep water for a ship with a block coefficient of .70 procceeding at speed of 12 knots.
S = 0.70 x 12 squared
__________________
100
S = 0.70 x 144
__________
100
S = 1.008 meters
Find the Sinkage in Shallow Water
S = 2 (0.70 x 12 squared)
__________________
100
S = 0.70 x 144
___________
50
S = 2.016 meters
What is the UKC of a ship with a draft of 8 meters, Cb of 0.70, traversing a water with a depth of 12 meters and the speed is 15 konts.
S = 2 (0.70 x 15 squared )
__________________
100
S = 0.70 x 225
__________
50
S = 3.15 meters
- 12 meters depth
___________________
8.85 meters
-8.00 meters draft
__________________
0.85 meters UKC
The Blokage Factor
Is the ratio between the ship's maximum underwater cross sectional area and the cross sectional area of the waterway where the ship is passing.
Example
The main draft of the ship is 6 meters and her beam is 15 meters , the submerged cross sectional area is 90 square meters, and if the width of the waterway is 25 meters and the depth of the water is is 20 meters the cross sectional area of the channel is 500 square meters The ratio therefore is 90 divided by 500 or 0.18 which is the blokage factor.
Relationship between blokag factor and Squat
The bigger the blokage factor the bigger the squat. That is why the squat in confined and shallow water becomes double than the squat in deep and open water.
Example
The main draftof a ship is 8 metersand her beam is 18 meters, if the width of the waterway is30 meters and the depth is 20 meters what is the blokage factor?
8 x 18 = 144
30 x 20 = 600
144
_____
600
0.24 is the bloking factor
Example
If the mean draft of your ship is 8 meters and her beam is 16 meters, what is the bloking factor if the width of the waterway is 30 meters and the depth is 25 meters?
8 x 16 = 128
30 x 25 = 750
128
______
750
0.1707 is the blokinf factor
Example
In Singapore strait where the depth of water is 13 meters, ship with block coefficient of 0.80 is travelling. What should be the speed in order for the ship to have a UKC of 2 meters if she has adraft of 9 meters?
13 - 9 = 4 meters
4 - 2 = 2 meters sinkage
S = 2 (Cb x V squared)
______________
100
2 = 2 (0.80 x V squared)
___________________
100
2 = 0.80 x V squared
_______________
50
V squared = 100 x 0.80
V Squared = 125
V = 11.18 is the speed of the ship
Example
In Malacca strait where the depth of water is 25 meters, a big container vessel with a draft of 18 meters and a block coefficient of 0.80 wants to proceed at its fastest safe speed maintaining an underkeel clearance of 5 meters. What speed should she use?
Depth = 25 meters
Draft = 18 meters
_____________
7 meters
UKC = 5 meters
____________
Sinkage= 2 meters
S = 2 (Cb x V squared)
________________
100
2 = 0.80 x V squared
_________________
50
100 = 0.80 x V squared
V squared = 100
_____
0.80
V squared = 125
V = 11.18 Knots
Bank Cushion and Bank Suction Effects
As the ship moves forward, the displaced water moving from astern builds up between the bow and the banks resulting in the bow being pushed away from the bank. the water rushing towards the stern between the ship and the banks drops i pressure more than on the other side of the ship on account of its faster flow . the lowest pressure drop occur near the stern of the ship so that the ship's stern moves toward the bank. Because of this since the bow is moving away fro m the bank the attraction of the stern towards the bank is made faster. The movementof the bow away from the bank is known as bank cushioneffect ad the movement of stern towards the bank is called bank suction effect.
Rounding a narrow River or Channel Bends
Where there is current the flow is fastest near the concave bank of the bend and it is slow near the convex bank. The convex bank is also known as the point. When negotiating a bend where the current is astern that is following the ship stay near the convex bank so that when the ship starts to turn the current strikes the quarter and pushes the ship's stern sideways making the stern turn at afaster rate .
If proceeding against the currnt, it is advisable to do it near the concave bank of the bend.
Inter action Between Ship's Passing close to Each other
When two ships are moving at full speed and pass close to its other , the drop in pressure of the water betwwen them combines and cause both or one of them to swing off course and cause bodily sideways movement towards or awaay from each other . This interaction effeect is more serious when the two ships are going violently on in one direction because the effect will be acting at longer time than when they are going on opposite direction.
When a ship is approaching close to a shoal her bow may suddenly move towards the shoal and then violently moves away from it . This behavior of the ship is called smelling the ground.
- Professor: Saliong Dionisio T
- Enrolled students: 24