Shiphandling With Tugs - Slesinger Flashcards
What are the three general categories of tugs used in shipwork?
- Conventional tugs
- Tractor tugs
- ASD tugs
ASD stands for Azimuth Stern Drive.
What are the five key elements in tug design?
- Towing point
- Propulsion point
- Maneuvering lever
- Propulsion and steering.
- Hull shape, super structure and steering
These elements are crucial for the effectiveness and safety of tug operations.
What is the towing point?
The point on the tug where the tow line is attached.
3. The last physical point on the tug that fairleads its line; or the contact point between tug and ship when the tug is pushing.
What is the propulsion point?
The point where the tug generates thrust. 4. The focal point of the tug’s application of horsepower under the water.
What is the maneuvering lever?
The distance between the towing point and the propulsion point. 5. The distance between the towing point and the propulsion point.
Describe the length and orientation of the maneuvering lever for Conventional tugs, tractor Tugs and ASD Tugs.
- Conventional Tugs- towing point forward of propulsion point, maneuvering lever short
Tractor Tugs-Towing point aft of propulsion point, maneuvering lever moderate
ASD Tugs- Towing point forward of propulsion point, longest when towing point is the bullnose- shorter when the towing point is the tow bitt.
What causes a tug to capsize while on a tow line?
Excessive lateral forces or loss of stability. 7. When the tug does not have enough leverage to counter the pull of the towline.
What advantage does a single-screw tug have over a twin-screw tug?
Simplicity in design and maintenance. 8. Efficiency, since on a horsepower for horsepower basis, a single-screw tug will develop about 20 percent more thrust.
What is the principal disadvantage of a single-screw tug?
Limited maneuverability. 9. Lack of maneuverability, inability to steer astern, and inability to maintain position (i.e., 90º) when backing. Power astern is less than power ahead.
What advantage does a twin-screw tug have?
Improved maneuverability and redundancy. 10. Excellent maneuverability, ability to maintain position when backing (if ship is stopped), and ability to steer astern.
What are the disadvantages of the twin-screw tug?
Increased complexity and maintenance costs. 11. May require a stern line when backing, is less efficient than a single screw tug. Backing power is less than ahead.
What advantages does a tractor tug have over a conventional tug?
Better control, stability, and ability to push or pull effectively. Can steer when going ashore. Has Omni-directional thrust. Does not have the same risk of capsizing as a conventional tug.
What advantages does an ASD have over a tractor tug? ( 5 things)
Enhanced maneuverability and versatility in operations. Better sea keeping ability , shallower draft, more efficient in converting horse power to bollard pull and can perform transverse arrest (Tractor tug can not)
What are the drawbacks of a CPP system?
- High costs, susceptibility to damage. A vessel’s steering qualities are affected when in neutral pitch. Since the propeller is always turning, it is liable to foul lines in shipwork.
- Increased maintenance requirements
- Higher complexity
- Potential for mechanical failure
Despite their advantages, CPP systems require careful upkeep.
What factors determine a propeller’s efficiency?
- Quality and velocity of water flow; and number, pitch, shape, size, and speed of the rotating propeller blades.
- Design shape
- Material
- Operating conditions
- Size
Each factor plays a role in the performance of the propeller.
How do nozzles increase propulsion efficiency?
- The propeller turns within a shroud which increases thrust 15 percent to 60 percent more than an open propeller.
By directing water flow and reducing turbulence
Nozzles enhance thrust generation and overall propulsion effectiveness.
What are the disadvantages of nozzles?
- They present more drag and lateral resistance underwater, hindering maneuverability and light tug running speed.
- Increased drag at certain speeds
- Higher construction costs
While beneficial, nozzles can have trade-offs in certain scenarios.
What three factors determine a rudder’s efficiency?
- Velocity of water flow, quality of water flow and rudder shape.
- Shape and area
- Angle of attack
- Speed of the vessel
These factors influence how effectively a rudder can steer a vessel.
What is the difference between an unbalanced and balanced rudder?
- Balanced or semi-balanced rudders are constructed so that the leading edge of the rudder extends forward of the rudder post.
This is done to provide more effective steering and a mechanical advantage to the steering gear.
Unbalanced rudders have a greater area behind the pivot point, while balanced rudders have equal area on both sides
This design difference affects the force required to turn the rudder.
What is a spade rudder?
A “spade” rudder is one that is not supported at the bottom by an extension of the vessel’s keel or skegs.
It alters the direction of rotation to enable reverse thrust
A type of rudder that is mounted on the hull without a supporting structure
Spade rudders are known for their high efficiency and responsiveness.
What is the difference between a steerable nozzle and a steerable propeller?
- A steerable nozzle around a fixed propeller. A sterotating the angle of the nozzle around a fixed propeller. A steerable propel. ler changes angle of thrust by rotating the propeller around a vertical axis.
A steerable nozzle directs water flow while a steerable propeller rotates to change thrust direction
Both systems improve maneuverability but operate differently.
Why are flanking rudders effective when operating astern?
- Flanking rudders are installed ahead of the propellers, and there are usually two of them for each propeller. They are more ef fective when operating astern as they are on the discharge side of the propeller.
They provide additional lateral control and enhance maneuverability
Flanking rudders assist in reversing by improving steering response.
Describe the Voith-Schneider cycloidal propeller.
- The VSP functions like a controllable pitch propeller rotating around a vertical axis. Vertical blades are attached to a rotating rotor casing. The rotor turns while each vertical blade oscil-lates, changing its angle (pitch) at points along the circumference of the rotor casings track.
A propulsion system that uses rotating blades to generate thrust in multiple directions
This system is particularly effective for vessels requiring high maneuverability.
What are the disadvantages of a VSP?
- VSP horsepower to bollard pull ratio is lower than conventional or steerable propeller tugs; VSP tug will have a deeper draft than a conventional or ASD tug, VSP systems are expensive compared to a steerable propeller or conventionally propelled tug.
- Complexity in design
- Higher maintenance demands
VSPs can be more challenging to manage compared to conventional systems.
Describe a steerable propeller system.
- Engine power is transmitted through a shaft to the upper casing of the drive unit housed inside the tug. A pneumatic or hydraulic clutch regulates the connection between engine output shaft and drive unit input shaft. A series of right-angled gears and shafts converts the horizontal rotation of the engine output shaft into the horizontal rotation of the propeller shaft. The lower drive unit houses the propeller and can be rotated through 360 degrees by mechanically or electrically driven hydraulic motors
A system that allows the propeller to change direction for improved maneuverability
Steerable propellers are beneficial for tugs and vessels needing precise control.
What is bollard pull?
- Bollard pull is the pull in pounds or kilos generated by a tug pulling against a fixed object. In conventional tugs it is estimated to be about one long ton (2,240 pounds) per 100 hp, depending upon the configuration of the tug and whether or not nozzles are installed. Bollard pull can range between 22.5 and 38 pounds per hp.
A measure of a tug’s pulling power, indicating its ability to tow a vessel
Bollard pull is crucial for evaluating a tug’s capabilities.
Is bollard pull a fair criterion for judging a tug’s serviceability for shipwork?
- Not always since other factors, like “stiffness” and maneuver-ability, are important too.
Bollard pull can be affected by the tug’s trim, and the number and kind of hull appendages that affect the water flow to the propeller.
Bollard pull is the common criterion for judging a tug’s capability.
However, other factors must be considered when evaluating a tug’s suitability for shipwork, including maneuverability, stability, and backing power. A deficiency in any of these may limit a tug’s usefulness even if its power is acceptable.
Bollard pull is a standard metric for assessing a tug’s operational effectiveness.
True or False: Z-drive propellers or SPS usually have Controllable Pitch Propellers.
False they are mostly fixed pitch.
True or False: VSPs have controllable fixed propellers.
True
CPP Propellers are _______ at going astern then fixed pitch propellers.
A. More efficient
B. Less efficient
B. Less efficient they only develop 40 to 45 % max ahead thrust.
Ducted propellers can produce ______ to _____ percent more thrust than unducted propellers.
15 - 60%
An open fixed pitch propellers running astern will produce roughly _____% of its ahead thrust.
60 %
This is the theoretical distance a propeller moves forward in one revolution.
Propeller Pitch
This refers to the potential amount of power loss between propeller and vessel speed.
Slip
The new synthetics that have the highest strength to weight ratio of any fiber for tow lines are? Two popular trade names for these fibers are?
- Aramid and HMPE
- Spectra and Dyneema
True or False: Lines made with HPME fibers float.
True
How many flanking rudders per prop are there generally? What is the advantage of having flanking rudders?
- 2 per prop
- They help the tug steer astern. they are generally kept midship when the tug is maneuvering ahead.
Which handles the quicker astern?
A. A tug with flanking rudders
B. A tug with steerable nozzles
C. they handle the same
A. A tug with flanking rudders
What is the benefit of having a steerable nozzle with a single screw tug?
It diminishes propeller torque when operating astern.
What does the term flanking mean when referring to twin screw tugs?
Moving the tug laterally in one direction or the other.
If a twin screw fixed pitch tug wants to flank to Starboard how are the propellers arranged and the rudder?
Port Engine Ahead, Starboard Engine Astern and port rudder
True or False: An ASD tug can produce lateral motion with the same speed an strength as a tractor tug.
False, It does not produce lateral motion with the same speed and strength.
What three factors must a tug operator balance when maneuvering around ships?
- Tug hull resistance, opposing forces, application of force to ship
These factors are crucial for safe and effective tug operations.
Hydrodynamic interaction between ship and tug are a function of which three factors?
- Ship Speed, displacement, and hull shape
Speed, distance, and angle of approach
Understanding these factors helps in predicting the tug’s behavior.
What is stemming?
- Stemming” can occur when a tug takes a towline from the bow of a moving ship. If the tug comes in contact with the ship’s side it may lose steerage, in which case the tug may be caught by the ship’s bow and rolled over.
The process of maintaining the tug’s position against the ship’s movement
Stemming is crucial for effective tug operations, especially in strong currents.
What are two common cases of stemming?
- Misjudgment of the tug’s set in towards the ship’s bow or oversteering as the tug transits through the ship’s pressure zones at the its bow. When the tug is overtaking the ship by the bow the bow wave could push the bow of the tug off and if the operator over corrects and continues to overtake he could have the same positive pressure continue to make the tug turn into by pushing the stern of the tug off.
Alongside a moving ship and in strong currents
These scenarios often require careful tug handling to ensure safety.
True or False: relative to the ship water flows faster near the ship’s hull than farther away.
True. The increase in water speed causes a negative pressure. As the water moves toward the stern the negative pressure is accentuated by the prop and then turns into a relatively weak high pressure in the ship’s wake.
What are the four hazards a tug operator needs to be aware of when approaching the stern of a vessel?
- Suction towards the stern.
- Rake or tumble home of the ship is a structural hazard.
- The ship’s turning propeller.
- The ship changing course.
What does the intensity of the high-pressure zone at the ship’s bow depend on?
A. Ship speed
B. Bow shape
C. Draft
D. All of the above
D. All of the above
What is the safest side for a tug to approach the bow of a tug underway?
A. Leeward side
B. Windward side
C. Inshore side
D. Offshore side
A. Leeward side
What is the most critical factor in passing a tow line?
A. Tug position
B. Ship’s Draft
C. Ship’s speed
D. All the above are equally critical.
C. Ship’s speed
What tug has a distinct advantage over conventional tug when it comes to passing a tow line to the bow of a vessel underway?
A. ASD tug operating stern first
B. ASD tug operating bow first
C. All of the above
D. None of the above
B. ASD tug operating stern first
They can extricate themselves from a potential stemming situation by steering away from the vessel.
True or False: An ASD tug operating bow first near the bow of a vessel underway shares the same risks as a conventional tug.
True
Ship’s interactive forces ________ with the ship’s speed.
A. Stay the same
B. Reduce exponentially
C. Grow exponentially
D. Grow slightly
C. Grow exponentially
The water in the ship’s prop wash may be moving ______ ________ than the ship’s wake outside the wash zone.
A. 2-3 kts faster
B. 2-3 kts slower
C. 1-2 kts faster
D. 1-2 kts slower
A. 2-3 kts faster
Ideally the ship speed is ______ kts or less and the ship’s propeller is stopped when a tug is making fast.
7 kts or less
If the pilot must make a change in __________ he should communicate with the tug operator.
A. Rudder
B. Engines
C. Speed
D. A and B only
D. A and B only
It is always prudent, if the ship will not be put at risk, to _______ the propeller when casting off the tug.
A. Not change
B. Stop
C. Increase
D. Decrease
B. Stop
What is an additional advantage of tractor and ASD tugs over Conventional tugs?
A. They can both perform transverse arrest
B. They are both capable of indirect towing
C. They can both transition from towing to push/pull mode without disconnecting the tow line.
D. All of the above
C. They can both transition from push to pull mode without disconnecting the two line.
At what speed should a tug transition to a push/pull position?
A. 7-8 kts
B. 5-6 kts
C. 3-4 kts
D. 1-2 kts
D. 1-2 kts 2 kts or less.
Once the tug operator has safely maneuvered a tug into position and made fast to the ship, he can declare to the pilot what?
A. In position
B. In position and ready to work
C. Standing bye to work
D. None of the above
B. In position and ready to work
What are the two components of the Center of Hydrodynamic Pressure?
- Lift and Drag
Lift and drag
The two components are vertical and horizontal forces.
The Center of Hydrodynamic Pressure is critical for understanding how forces interact with vessels in water.
How should a tug’s line be cast off from the ship to the tug?
• The ship’s mates on the bow and stern should direct their deck crews to slowly lower the tug’s line and tagline unless directed to drop it by the tug’s operator. Dumped lines have potential to cause serious injury to the tug’s deck crew as well as foul the ship or tug’s propulsion units.
The line should be cast off smoothly and without sudden jerks.
This ensures safety and prevents accidents during the towing process.
Why is towline work on a conventional tug dangerous?
- The tug’s towing point is forward of the propulsion point which can make the tug susceptible to tripping or girting.
Because of the risk of tripping or girting.
These actions can cause loss of control and accidents.
Explain how a conventional tug trips or girts.
- Tripping or girting the tug can be caused by the ship overtaking the tug, or when the tug’s thrust and maneuvering lever cannot counteract the force of the tug’s center of hydrodynamic pressure acting on the tugs turning lever.
A tug trips or girts when it loses stability due to an unexpected shift in forces.
This can occur during maneuvers or when the towline is not managed properly.
How can the tug handler best avoid tripping or girting?
By employing tractor or reverse tractor tugs or requiring that the ship go at slow-to-moderate speeds. This risk can be managed by mechanical means moving the towing point through the use of hold downs and a gob rope.
By maintaining proper tension on the towline and adjusting to vessel movements.
Awareness of the surrounding conditions is crucial.
What is the advantage of using a tug alongside?
- It takes less time for the ship to respond to the tug’s efforts, and working the tug alongside is safer than towline work.
It provides better control and stability during maneuvers.
This technique is often used in tight spaces or when precision is necessary.
When does a conventional tug use a quarter line?
The conventional tug uses a quarter line to maintain a position approximately at right angle to the ship when backing, otherwise the effect of the torque of the tug’s own propeller, the vessel’s motion, or wind and current might move the tug out of position.
When additional control is required during towing maneuvers.
The quarter line helps in adjusting the angle of pull.
Explain a wrap line.
- A wrap line is line used by a tug to steer the bow of a ship moving stern first. It is led from one side of the ship’s bow to the bullnose on the tug located on the opposite side of the ship’s bow. This allows the tug to steer the bow in either direction.
A wrap line is a line that wraps around a vessel to provide additional towing support.
This technique can enhance stability and control.
Can a tug work a wrap line on all vessels?
- No. Bulbous bows, severely raked stems, and ships with flare may prevent a tug from working in this position.
No, it cannot work a wrap line on all vessels due to size and shape limitations.
The effectiveness of this method depends on the specific vessel configuration.
What is meant by the term snapping a tow?
- This occurs when a tug with a ship or barge in tow astern makes a hard turn and at the same time applies more power.
Since the tug’s rudder will set the stern of the tug in the opposite direction, the bow of the towed vessel will often also be set in the opposite direction of the turn at first.
Snapping a tow refers to the sudden release of tension in the towline.
This can lead to dangerous situations if not managed properly.
Why should a tug made up for breasted towing have tight lines?
- If there is too much slack in the lines, the tug’s angle to the ship’s centerline will vary and detract from the tug’s ability to apply effective steering forces.
Tight lines prevent slack that can lead to uncontrolled movements.
Ensuring tight lines is crucial for maintaining safety.
Why is indirect towing so powerful?
- Indirect towing uses the tug’s hydrodynamic resistance to add force to the towline.
Because it allows for greater leverage and control over the towed vessel.
This method is particularly effective in challenging conditions.
How is indirect towing used to advantage?
- Indirect towing can be used to provide steering and braking forces at ship speeds that are too high for effective direct towing.
It is used to maneuver larger vessels more effectively.
Indirect towing can provide better handling in tight situations.
Why should a tug back easily on a slack headline?
- Because the momentum of the tug moving astern could develop enough force to part the line.
To prevent sudden jerks that can destabilize the tug or the towed vessel.
Managing slack is important for maintaining safety.
What are the principal causes of accidents involving tugs doing shipwork?
- Human error, mechanical failure, and weather.
The principal causes include equipment failure, human error, and environmental conditions.
Understanding these causes is vital for improving safety protocols.
Of the causes cited which is the most common and why?
- Human error in regards to excess speed, because if it is on the part of the ship, it can overpower a tug on a towline and trip or girt it. Excess speed can also capsize a tug using a quarter line and even endanger a tug fast alongside with only a head line out. It will also destroy the tug’s ability to assist the ship. When the tug uses excess speed, it can part lines (injuring personnel) and lead to collisions with the ship it is assisting.
Human error is the most common cause due to misjudgment or lack of experience.
Training and awareness can significantly reduce this risk.
Assist tugs use what four basic positions in shipwork?
- Leading tug towing on a line
- Tug alongside the ship pulling on a line or pushing
- Tug alongside the ship breasted or “on the the hip”
- Trailing tug, pulling on a line or pushing
What term describes a tug working a head of the ship moving forward? Astern of a ship moving forward?
- Lead tug
- Tail tug
True or False:
Effective application of a tug pushing, pulling, or working a towline can be achieved only if both pilot and tug operator understand the dynamic balance between a tug’s center of hydrodynamic pressure, lift-and-drag forces, maneuvering and turning resistance levers, and applied horsepower (fig. 9-1).
True
A tug’s hydrodynamic resistance increases as the square of __________.
A. Draft
B. Trim
C. Velocity
D. none of the above
C. Velocity
The amount of force applied to the towline is a function of the tug’s thrust and steering forces combined with __________ forces.
A. Hydrodynamic Lift
B. Hydrodynamic Drag
C. Hydrodynamic Velocity
D. A and B only
D. A and B only
What are the two forces that come into play where a tug has moved to a position where its towline angle approaches the desired angle?
A. Turning Lever and Maneuvering Lever
B. Turning Lever and Hydrodynamic Lever
C. Maneuvering Lever and Steering Lever
D. None of the above
A. Turning Lever and Maneuvering Lever
The turning Lever is the distance between ________ and ________.
Center of Hydrodynamic Pressure and Towing Point
The Maneuvering Lever is the distance between the tug’s _________ point and _______ point.
Propulsion Point and Towing Point
On a conventional tug it counters a turn by moving the tugs stern and towing point away from the ship, what does this do?
Adds the tugs pull on the towline in the opposite direction to the tow.
A sign that the hull’s hydrodynamic forces are strengthening is what?
The sensation of “digging” in
What is a clear sign that the tug is on or past the precipice of losing its maneuverability?
When it reaches the point of deck edge immersion
Conventional tugs are very effective in the position of __________________
Lead tug on a tow line it can apply forces equally in both the port and starboard directions.
When a conventional tug on a towline begins a turn the bow of the ship may be set in what direction initially?
Directly opposite the intended turn direction
True or False: tractor tugs as lead on a tow line do not have the same hydrodynamic advantage as a conventional tug in the same position.
True, this is because the tractor tug must use more of its power to stay in position and pull its own hull through the water there by reducing actual pull on the tow line.
An ASD tug working bow to bow has the advantage of what? But the disadvantage of what?
- Longer maneuvering lever
- Operating skeg first
When working as a lead tug on a line both tractor and ASD (reverse tractor) have distinct ______ advantages over a conventional tug.
Safety because of their Omni-directional thrust capability and prop first orientation it makes them less likely to trip or girt.
The effectiveness of all tugs working as a lead tug diminishes as ship _________ increases.
Speed
The head line is also referred to as what?
Backing line
Stern lines and ______ are interchangeable terms.
Quarter lines
The magnitude of a tug’s pushing force against a ship’s side is a result of the aggregate effect of what four factors?
- Pushing angle of the tug in relation to the fore and aft line of the ship
- Amount of the tug’s hydrodynamic lift
- Amount of the tug’s thrust allocated for steering
- Efficiency of the tug’s maneuvering leverage
The key determinant to the required allocation of steering force is the proportional relationship between what two levers?
- Maneuvering Lever distance between tow point and prop point
- Turning Lever: distance between towing point and the center of hydrodynamic pressure.
When a tug is pushing on a ship DIW where is the towing point and where is the center of hydrodynamic pressure?
Both at the bow of the tug
As the ship begins to move forward what happens to the Center of hydrodynamic pressure?
It moves aft
Where is the center of hydrodynamic pressure on a conventional tug compared to a tractor tug or ASD?
Further aft. This increases the turning lever making it harder to overcome
What are the three lines used when a tug is breasted up or on the hip?
Headline, spring line and stern line
True or False: it is important that the tug be secured parallel to the ship’s centerline with its propulsion units as close to the end of the ship as possible when towing on the hip.
True, this gives better leverage in applying steering forces to the ship.
What are two reasons most tugs can only make up alongside the flat of the ship’s hull?
- They avoid contact between superstructure of the tug and hull of the ship.
- The tug is more secure and less likely to yawn on the lines if more surface area near the tugs propulsion end is in contact with the ship.
What are the two ways a conventional tug can work as a trailing tug?
- Off its stern with a towline
- Off its bow with 1 or 2 headlines
When is it safer to shift the towing point all the way aft to a position over the prop as a conventional tug on a tow line?
A. When it is providing only steering forces
B. When it is providing only braking forces
C. When it is indirect towing
D. None of the above
B. When it is providing only braking forces
When towing circumstances call for more ship speed a conventional tug is safer ________ as a trailing tug.
A. Acting as a rudder tug going bow first
B. Indirect towing
C. Going stern to stern with a gob line
D. None of the above
A. Acting as a rudder tug going bow first
True or False: A conventional tug can be very effective functioning as a trailing tug off the bow of a ship with stern way.
True
What orientation do ASD and tractor tugs operate when acting as a trailing tug or rudder tug?
ASD: Bow to stern of vessel
Tractor: Stern to stern of vessel
At what ship speeds can an ASD and Tractor tug provide steering forces when Direct towing?
A. 3-4 kts
B. 4-5 kts
C. 5-6 kts
D. 6-7 kts
C. 5-6 kts
This is the technique that the tug operator adds to indirect towing line forces by moving the tugs towing point farther off to the ship’s side and applying full power.
Power indirect
In power indirect mode the towline angle approaches _____ºs and has the potential of applying up to _____% of the tugs rated bollard pull to the tow line.
- 90º
- 120% (between 75% and 120%)
What are determining factors in establishing safe limits of indirect towing at maximum ship speed?
A. Tug stability
B. Tug freeboard
C. Tug bollard pull
D. All of the above
D. All of the above also skeg design, towing and propulsion point locations.
Forces generated by indirect towing are a result of what factors? (4 things)
- Towline angle in relation to the ship
- Tug angle in relation to the towline
- Speed through the water
- Allocation of the tugs thrust to steering
what option does a tug operator have if the tow line force becomes too much during indirect towing?
A. Steer back toward the pulling force
B. Reduce the angle to water flow and hydrodynamic resistance
C. Reduce power and slow down
D. All of the above
D. All of the above
A maneuvering allowing a quick repositioning of the tug from indirect to direct towing in which the tug operator can use combination of towline tension, render the recovery feature of the winch and the tug’s lateral maneuverability to swing around into the direct towing position is what?
Jackknifing
At what speed does jackknifing start to be an appropriate maneuver?
A. 1-2 kts
B. 2-3 kts
C. 3-4 kts
D. 5-6 kts
C. 3-4 kts
True or False: Towlines or headlines with a steep angle put an undo strain on the line and its connecting gear.
True
When pulling full on a line and an order to stop the engine is received what should the tug operator do?
Drop the engine to a slow speed first and then stop
What lines should never be used in shipwork?
Nylon lines
Most mechanical failures can be attributed to a breakdown of _________ and _________ systems.
Steering and Propulsion systems.
What three fundamental principles of shiphandling are essential to a shiphandler’s eye?
- Center of Lateral Resistance 2. Pivot Point 3. Maneuvering levers
The Center of Lateral Resistance determines the resultant proportion of _____________ vs. _______________ force of an applied lateral force to the ship.
Lateral vs. rotational
Where is the pivot point located for a ship that is stopped?
Amidships at the CLR depending on the draft and trim
Where is the pivot point located for a ship that is moving laterally?
Amidships at the CLR depending on draft and trim
Where is the pivot point located for a ship that is moving ahead?
Approximately one quarter ship length aft of the bow
Where is the pivot point located for a ship that is moving astern?
Approximately one quarter ship length forward of the stern
Where is the pivot point located for a ship that is turning?
Approximately one third ship length aft of the bow
The pivot point functions as the _______ of the ship’s maneuvering lever.
fulcrum
If a tug is meant to turn a vessel where is the best placement for it?
A. Positioned on the fulcrum
B. Positioned a ship width forward of the fulcrum
C. Positioned a ship width aft of the fulcrum
D. As far away from the fulcrum as possible
D. Positioned as far away from the fulcrum as possible.
If a tug is meant to turn a vessel where is the best placement for it?
A. Positioned on the fulcrum
B. Positioned a ship width forward of the fulcrum
C. Positioned a ship width aft of the fulcrum
D. As far away from the fulcrum as possible
D. Positioned as far away from the fulcrum as possible.
If a tug is meant to move a vessel laterally where is the best placement for it?
A. Positioned on the fulcrum
B. Positioned a ship width forward of the fulcrum
C. Positioned a ship width aft of the fulcrum
D. As far away from the fulcrum as possible
A. Positioned on the fulcrum
This is the point on a ship where the application of a lateral force results in the ship moving sideways with no rotation.
The center of lateral resistance
The CLR is not fixed and reflects the balance pint of what factors? (3 factors)
- Hull shape
- Direction of the ship’s motion
- Draft and Trim
Where does the CLR move when the ship gains headway? Stern way?
- Moves forward
- Moves aft
True or False: the Center of Lateral Resistance of a ship down by the stern is farther aft than one trimmed forward.
True
True or False: the location of the center of lateral resistance is often the same location as the pivot point.
False. It is often not in the same location
This is the point appears on the ship as an axis of rotation with reference to the water’s surface.
The pivot point
True or False: the pivot point is the result of applied forces and the subsequent motion of the ship.
True
Where does the pivot point move in relation to the vessels movement? In relation to applied lateral force?
- Toward the direction of vessels movement.
- Away from applied lateral force.
What are the five basic ship movements?
- Stopped
- Lateral
- Headway
- Stern way
- Turning
Where is the pivot point of a ship in relation to the center of lateral resistance on a ship with lateral but no rotational motion?
At the same location
Where is the pivot point after a ship first starts to come ahead?
A. 1/2 L from bow
B. 1/4 L from Bow
C. Far forward
D. Amidships
C. Far forward
Where is the pivot point after a ship gains headway?
A. 1/2 L from bow
B. 1/4 L from Bow
C. Far forward
D. Amidships
B. 1/4 L from bow
When a ship initiates are turn and lateral resistance builds on the ship’s side what happens to the pivot point?
A. Stays at the same spot
B. Moves aft of its usual spot
C. Moves forward of its usual spot
D. None of the above
B. Moves after of its usual spot. Usually 1/3 L from the bow.
The ship’s maneuvering lever is defined by the relationship between what two factors?
- Pivot point location
- Ship propulsion forces
The Maneuvering lever of a ship may either lengthen or short in accordance with the ship’s motion and what?
The magnitude of the force being applied to the end of the lever
The art of ship handling with tugs is teh ability to apply the power of tugs within the context of the ship’s pivot point and in conjunction with ______________.
The ship’s maneuvering lever.
Define a tug’s assist lever.
- The distance between the location of the tug’s applied force and the ship’s pivot point.
. The
A lever that helps a tug apply force to a ship while maneuvering
The assist lever is crucial for enhancing the tug’s effectiveness in towing and positioning.
Why is it easy for a ship with headway to overwhelm a lead tug on a towline?
- The ship has greater power and can apply that power on a longer and more efficient maneuvering lever. This can easily overpower the tug.
Because the ship’s forward momentum can exceed the tug’s pulling capacity
This phenomenon can lead to loss of control over the towline.
What are the three means a tug has to apply force when working?
- Push, act as a drogue or pull on a line.
- Direct pull
- Side pull
- Push
Each method has its advantages depending on the situation and desired maneuver.
What are the four factors that affect a tug’s effectiveness when working alongside?
Angle of the tug, offset position of the tug, drag force and tug’s applied horsepower.
- Tug size
- Tug power
- Ship size
- Environmental conditions
These factors determine how well a tug can assist in maneuvering the ship.
Why is a conventional tug backing on the stern quarter, on the outboard side of a turn, ineffective in turning the ship?
- At all but the lowest speeds the conventional tug allocates almost all its horsepower to maintain position at, or close to, 90.
There is minimal lateral pull applied to the tug’s headline tug’s angle, offset position, drag, and horsepower are all working on a long assist lever to counter the turn.
ll.
Because it cannot generate sufficient force to change the ship’s direction
This position often leads to a loss of control over the ship’s movement.
In breasted towing, a tug made up on the ship’s stern creates, in effect, a _______.
Twin screw
[pushing force]
This configuration helps in maintaining the ship’s heading and stability.
In breasted towing, a tug made up on the bow functions as a _______.
- Steerable bow thruster.
[pulling force]
This setup assists in steering the ship and controlling its speed.
What is negative water flow?
- Negative flow considerably increases the torque loadings on the propeller and engine. High negative water flow may increase the load enough to stall, or damage, the tug’s engine, clutch, or couplings.
Water flow that moves against the direction of the ship’s movement
Negative water flow can complicate the tug’s efforts in maneuvering.
How is negative water flow a factor in conventional tug performance?
- Negative flow considerably increases the torque loadings on the propeller and engine. High negative water flow may increase the load enough to stall, or damage, the tug’s engine clutch, or couplings.
This situation may require adjustments in tug positioning and strategy.
Why is a trailing tug the most effective position for steering a ship?
- A trailing tug creates the longest assist lever and allows the tug to apply equal forces to both starboard and port. The tug can enhance the effect of the ship’s rudder on a ship with headway and can also control the bow and steer a ship with sternway
Because it can exert force in the direction of the ship’s movement
This position allows for better control and responsiveness.
What precautions should the shiphandler exercise when employing a conventional tug as a trailing tug on a towline?
- The shiphandler must execute careful management of ship speed and propulsion wash.
Ensure proper communication and coordination with the tug
This helps to prevent accidents and ensure effective maneuvering.
What two methods can tractor and ASD tugs use to steer a ship as a trailing tug?
- A tractor or ASD tug can utilize direct towing at ship speeds of five knots or less, and indirect towing at higher speeds
- Pivoting
- Side pulling
These methods enhance the tug’s ability to control the ship’s heading.
What is the essence of effectively using tugs to steer and propel ships?
- Steering and propelling ships with tugs is a matter of creating and using the tug force as an effective lever in conjunction with the ship’s maneuvering lever.
Coordinated force application and positioning
Effective tug operations rely on teamwork and strategic maneuvering.
A shiphandler’s effective use of tugs to steer and propel ships requires an awareness and appreciation of three maneuvering factors what are they?
First, the pilot must understand the relationship between tug location and the ship’s pivot point.
Second, he must be cognizant of the orientation of both the tug’s position and the ship’s propulsion point in reference to the ship’s pivot point.
Third, he must account for the strengths and weaknesses associated with the four basic tug positions in ship assist.
What tug position is the optimal position to steer a ship with headway?
A. Tug on a tow line on the bow
B. Tug at or near the stern
C. Tug on the hip midship
D. Tug on the shoulder of the bow
B. Tug at or near the stern
What determines the length of the assistance lever of the tug and maneuvering lever of the ship?
A. Ship speed
B. Ship direction
C. Tug location
D. All of the above
D. All of the above
With a leading tug towing on a line the tug always has a force component that adds to ship ________.
Speed
What is the assistance lever of a tug towing on a line compared to the maneuvering lever?
Assistance lever is much shorter
True or False: With prudent use of the ship’s rudder and propulsion, the ship pilot can use a tug on a towline to control the ship’s bow and regulate the turn rate of the ship.
True
True or False: with a lead tug with a vessel with stern way it is difficult if not impossible for one tug to effectively steer the ship.
True, the pilot must steer judiciously using rudder and small kicks ahead.
With a lead tug along with a trailing tug with a vessel that has sternway what does the ship use its rudder and propulsion to do?
A. Nothing it is not effective while under sternway
B. Provides sternway
C. Shift and position the stern
D. None of the above
C. Shift and position the stern
With a tug alongside the ship pulling on a line or pushing what is critical?
A. The length of the quarter line
B. The length of the head line
C. The length of both lines
D. None of the above
B. The length of the headline to allow the tug to lie flat alongside and be more effective.
With a tug alongside the ship pushing if the tug is not at a 90º angle what component will the tug add to?
A. Ship speed
B. Rotational momentum
C. Lateral motion
D. All of the above
A. Ship’s speed or rate of advance.
When a tug lays passively on it line with engines stopped, the line is under tension created by the tugs weigh and hydrodynamic resistance. What is this called and in which direction may it turn the vessel?
Drogue effect and toward the tug
True or false: a tug alongside generally is not as effective pulling on its line as it is pushing into the ship.
True
Tug performance alongside depends on what?
A. Location of pivot point
B. Ship draft
C. Ship speed
D. None of the above
C. Ship speed
True or False: a tug alongside is quicker than a lead tug on a towline when responding to ship’s pilot orders.
True
What is true about a tug alongside the bow shoulder on a ship with head way?
A. This position gives a small to negligible assist lever to turn the ship
B. This position can steady and apply lateral forces to the ship’s pivot point
C. This tug can function as a dynamic spring line.
D. All of the above
D. All of the above
True or False a tug alongside the bow shoulder on a ship with head way when the tug is on the outboard side of a turn it can push to assist the ship’s maneuvering lever.
True
a tug alongside the bow shoulder on a ship with head way when the tug is on the outboard side which factor detracts from the vessel’s rate of turn?
A. Angle of the tug
B. Offset position of the tug
C. Drag force
D. Tug’s applied horse power
C. Drag Force
A tug alongside the bow shoulder on a ship with head way when the tug is on the inboard side and backing which factor detracts from the vessel’s rate of turn?
A. Angle of the tug
B. Offset position of the tug
C. Drag force and Tug’s applied horse power
D. None of the above
D. None of the above they all contribute to the rate of turn. Additionally the tug acts as a dynamic spring line.
A tug alongside the bow shoulder on a ship with head way when the tug is on the inboard side and backing on a line what is the weak link ?
The tug’s line. Always be mindful of speed.
When a tug is alongside the stern quarter what side is the best placement? Why?
The inboard side of the turn because if it pushes it accentuates the ship’s steering and propulsion.
What position is a conventional tug practically useless?
After quarter on the outboard side of a turn. Unless the ship is bare steerageway the tug will oppose the turn even when backing full.
When tractor or ASD tugs are alongside the ship’s quarter which way should they position their propulsion end? If they are required to pull how can they avoid loss of effectiveness?
- Propulsion end first
- Direct pull at about 45º to prevent wash hitting the ship’s hull.
If a tug is alongside the ship’s bow shoulder it has an excellent Assist lever when the vessel has sternway, how can the pilot steer the ship with the Rudder and propulsion?
By giving kicks ahead and using the tug to steady the bow.
True or False with a conventional tug alongside the ship’s bow shoulder it has the same limited or contrary effect as it does alongside the stern quarter of a ship with headway.
True
A tug alongside the ship’s stern quarter with sternway the tug can assist in moving the ship’s pivot point ________.
Laterally
What is the correct nautical terminology for a tug on the hip or hipped up?
Breasted or alongside towing
What happens to the vessel if a tug on the hip of the bow comes ahead or comes astern of a vessel with headway?
- The vessel will rotate away and gain speed.
- The vessel will rotate toward the tug and lose speed.
What statement is true concerning a conventional tug when breasted towing?
A. It is most effective when it propels or steers by coming ahead on its engines.
B. It is most effective when its bow if facing the direction of ship advance.
C. When it is made up with its stern facing the ships way it is limited in bollard pull and maneuverability.
D. All of the above.
D. All of the above.
Conventional tugs at what speeds can lay broadside to the general direction of ship’s advance as a trailing tug?
A. 1 - 3 kts
B. 2 - 4 kts
C. 4 - 5 kts
D. 5 - 6 kts
A. 1 - 3 kts with the use of a gob line
True or False a conventional tug can function as a trailing tug by working off its bow enabling it to apply force in both port and Starboard Directions.
True
Is the pivot point always near the ship’s center of lateral resistance?
No, The pivot point may coincide with the CLR when the ship is stopped but once lateral force is applied the pivot point is a moving target.
What is the effect on the ship’s pivot point of one tug pushing at the bow?
The pivot point moves from mid ships to the ship end opposite of the tug.
How many ship lengths will it take to turn a ship with one tug pushing at the bow?
Two ship lengths. When the tug starts pushing the ship gains momentum and begins to creep ahead.
What is the effect on the ship’s pivot point of two tugs pushing with equal force, one on the port bow and one on the port stern of a stopped ship?
They can turn the ship within one ship length and the pivot point stays in line with the Center of lateral resistance.
In order to move a stopped ship laterally, the external forces applied must have _______ on either side of the ship’s pivot point.
equal magnitude
What is drift angle?
The angle between the ship’s centerline and the direction in which the ship’s bridge is actually traveling in a turn.
Why is knowledge of drift angle useful to the pilot?
Drift angle serves as a visual cue for the pilot to estimate the degree of lateral motion or slide that a ship has as it executes a turn . It helps in navigating and maneuvering the ship effectively
The interrelation between the ship’s center of lateral resistance and its pivot point is most apparent when the tug pushes or pulls laterally on a ship that _____________.
A. Is moving ahead
B. Is moving Astern
C. Is stopped
D. Any of the above
C. Is stopped
True or False: if one force is stronger the pivot point of a vessel shifts toward the weaker force.
True
Moving a ship laterally requires the absence of ___________ consequences of forces applied to the ship’s turning lever.
Rotational
The ship’s pilot should be familiar with what principle of ship movement?
A. Pivot point movement
B. Drift Angle
C. Lateral motion
D. All of the above
D. All of the above
On a ship DIW when the pilot turns the rudder hard over and orders ship’s engines ahead the ship’s stationary inertia resists the ship’s forward motion. Where does the pivot point go?
1/8 ship Length from the bow
On a ship DIW when the pilot turns the rudder hard over and orders ship’s engines ahead the ship’s stationary inertia resists the ship’s forward motion. If the ship continues to turn where does the pivot point eventually go?
1/3 ship length from the bow
When the bridge of the ship is aft and the pilot makes a large turn what will the sense be from the bridge?
The stern skidding sideways in the turn
Full bodied ships such as bulk carriers usually have _______ drift angles?
Large drift angles
Finer narrower hulled ships have _______ drift angles.
Small
the tug can initiate the tum by pushing or pulling on the bow. The tug does this to take advantage of the long assist lever to the ship’s pivot point aft. As the ship comes read with the rudder hard over, the ship loses its aft momentum and tra pivot point migrates toward midships. At this point both ship and tug are working together to spin the ship within its own length. This presents another CDP. If the pilot allows the ship to gather headway, the pivot point rial moves very close to the bow, enhancing the effect of the ship’s rudder. As a result the ship’s maneuvering lever is rotating the body of the ship around its bow and the tug is no longer aftectively turning the ship. Here is yet another CDP.. This allows the ship to continue turning with minimal headway. If the tug lacks sufficient capability, the ship continues to gather headway and the tug may be overrun by the ship unless released. What are the three CDPs mentioned above?
One CDP when to apply the ship’s power and rudder.
The pilot can allow either the ship to gather headway or by giving short kicks ahead, keep the way off, allowing the ship to continue turning around its midships turning axis.
If the tug has enough maneuverability and power it can offer sufficient resistance to the ship’s headway to hold the ship’s pivot point in a position well forward
The interrelation between the ship’s forward inertia and the amount and location of the tug’s lateral force determines this?
The ship’s pivot point
When a ship gives a kick ahead with the rudder hard over, the ship’s inertia sustains a residual lateral motion after the propeller is stopped where on the vessel is this lateral motion more pronounced?
The Ship’s stern
When a ship is being pulled off the dock laterally by two tugs equal distance apart. The ship propulsion starts to engage ahead the ________ tug will lose leverage what are the two ways the tugs can regain balance?
- Forward
- A. If the stern tug reduces thrust
B. If the stern tug shifts to a position closer to the ship’s pivot point
What are the three principle techniques used by tugs to apply braking force to the ship?
- Tug’s weight
- Lateral resistance
- Bollard Pull
Or a combination of these three.
What is the prime function of tugs in shipwork?
A. To provide steering effect
B. To provide lateral movement
C. To provide longitudinal movement
D. To create braking effect
D. To create braking effect
The ship’s rudder requires a minimum amount of water flow. The velocity of this flow is the combined result of ship’s __________ and ___________.
- speed
- Propeller wash
As ship speed and propeller wash drop so does control of the ship.
What are the two ways a pilot uses the tug’s braking force?
- To bring the ship to a stop
- To provide sufficient drag to keep the ship speed down without actually bringing it to a stop.
What is the primary tools pilots use to manage speed?
Tugs
What are the two positions a tug can apply braking force to a ship?
- Alongside
- In-line aft
If a tug is alongside and using breaking force it will tend to can’t the ship in which direction?
The side the tug is on
How do tractor tugs or ASD tugs use bollard pull to create sufficient braking forces? (Two positions)
- Inline
- Reverse arrest
An ASD tug has the ability to use this position to apply breaking force that the other tugs do not. What is it?
Transverse Arrest
What factor or factors effect tug’s braking capability?
A. Ship Speed
B. Negative water flow
C. Ship’s propeller wash
D. All of the above
D. All of the above
When a tug reverses its thrust to slow a ship, the tug’s propulsion machinery must contend with the effects of ___________. Which may overload and stall engines of conventional tugs or tractor tugs using too much pitch.
Negative Water Flow
How can ASD tugs and tractor tugs with independently controlled thrusters manage negative water flow?
Turning its units at an angle to the tug’s center line.
ASD tugs can align their units anywhere between ______ position to __________ position to avoid the effects of negative water flow.
Reverse arrest to transverse arrest
Conventional and VSP tractor tugs may find it difficult to apply consistent, direct pull on the two line while keeping the tug inline aft because of the eddies associated with this area what technique can an ASD tug apply to that works well in these situations?
Transverse Arrest
True or False: To ensure they are effective in critical times where ship propulsion may malfunction the pilot must have prepositioned the tug in a manner that enables the tug to employ its most effective braking factors associated with the design and propulsion features of the tug.
True
What are the three phrases of ship handling task management in maneuvering ships with tugs?
- Initial assessment
- Create a maneuvering plan
- Adjust the plan
What are the factors in choosing the placement of tugs in Shipwork ?
Sequence of maneuvering events, safety of tug, limits of tug design, skill level of tug operator, need and location of highest horsepower tug, required allocation of tug’s horsepower to maintain or achieve assist position
What are the factors to be taken into account in the initial assessment?
- The ship (displacement, handling, functionality and reliability of the ships bridge resources)
- Human Resources (Master, mates and helmsman)
- Electronic resources (communication and navigation equipment)
- Communication reliability
- Weather (wind, current, visiability)
- Navigation conditions (water depths, channel constrictions, air draft restrictions, berth configuration, vessel traffic conditions)
What are the factors to be taken into account in the second phrase of creating a maneuvering plan?
the ship’s intended track to or from berth
the ship’s intended speed
the placement of tugs
identifying critical decision points (e.g., helm over points, points to initiate speed reduction procedures etc.) .
What are the factors to consider when doing the third phase of plan implementation and adjustment?
- sensing ship movement and changes in environmental
- planning future maneuvering steps, aware that his choice ofa maneuver at any one moment may restrict his choices later
- managing communication and trust relationships with the ship’s master, crew and tug operator,
- the best use of the assist tug’s application
True or False: A pilot’s ability to quickly sense changes (the gust of wind, the drift of the ship’s bow, and make quick and accurate adjustments is the mark of a skilled and experienced pilot.
True
These 8 principles will assist the pilot in his decisions.
- Anticipate the complete sequence of maneuvering events in which tugs will be used:
Note the points in the maneuver where the tug may have to switch position, transition from towing to a push/pull mode.Note where the tug’s push or pull will be critical to the success of the maneuver. Place tugs in positions based on the priority and critically of their use. - Factor in the safety of the tug
A. Avoid positions that place the tug between the ship and the dock or other fixed objects with no means of escape. - Factor in the limits and capabilities of specific tug designs
A. Put the most maneuverable tug in the position that requires the tug to shift.
B. Place a tractor or ASD tug in positions where a conventional tug would primarily have to back in order to be effective.
C. Use handy tugs (those with a low profile) to work near the ends of ships and under overhanging structures. - Factor in the skill level of the tug operator.
- When multiple tugs are used, position the most powerful tug where its horsepower is most needed:
a. This may be forward on a deep-loaded ship, or
b. aft on a ship in ballast. - Estimate the amount of the tug’s horsepower needed to keep the tug in the assigned positions versus the amount available to bush or pull on the ship.
- On large, deep-draft vessels, tugs are most effective working as far forward or aft as is safe or practicable.
- On smaller vessels or those of light draft forward, the bov tug may function better if secured farther aft than would be proper for a larger or deeper vessel
If a ship is being turned through the wind and is light where may the ship handler consider moving the leeward tug?
A. To the lee quarter
B. Center lead aft
C. To the windward bow
D. To the windward quarter
C. To the windward bow to check the swing of the ship before it has too much momentum.
What should the ship handler avoid when a tug is moving from one quarter to another?
Backing hard until the tug is fast
During a maneuver it helps to break it up into sections 4 parts of a maneuver which a ship handler can think of for placement of tugs are?
- Stop the ship
- Turn the ship
- Shift tugs
- Breast vessel to the dock
When making a bend with a tug it helps for the tug on the inside of the bend backs this does two things which are?
- Starts the swing
- Retards the speed making the prop and rudder more effective on the ship.
If the bend is sharp what will a tug on the inboard quarter do to help facilitate a turn?
A. Back to use a twin screw effect in conjunction with the ships prop.
B. Push if it has a head line up.
C. Act as a drogue
D. None of the above
B. Push if it has a head line up and can get to a 45º angle vessel speed must be kept low.
Why is maneuvering through a bridge or lock a challenging maneuver for a ship handler when considering the tugs?
A. Tugs must be able to apply steering force in a narrow area
B. Tugs must be able to apply breaking force in a narrow area
C. Tugs must be able to apply propulsion in a narrow area
D. All of the above
D. All of the above
What is the difference between handling a dead ship and assisting a powered vessel?
- With a “dead” ship the tug is the prime mover, with a powered vessel the tug is merely assisting.
Handling a dead ship involves managing a vessel without power, while assisting a powered vessel involves providing additional support to a vessel that is operational.
Handling a dead ship may require different techniques and more tugs compared to a powered vessel.
Is one tug ever used to handle a small ship by itself?
- Yes, just as tugs frequently handle fairly large barges unassisted.
Yes, one tug can be used to handle a small ship by itself.
If only one tug is used and a hard turn must be made, where should the tug be?
- The tug should be hipped up on the inboard side of the turn, since even if the tug backs the ship will continue to swing in the direction of the turn. If the tug (especially a single-screw tug) is on the outboard side of the turn, it may not be able to back as this would “kill” the swing.
The tug should be positioned on the outside of the turn.
How may a tug on the outboard side of a turn reach a point of no return?
- If the ship’s turn rate is too slow and there is neither sufficient room ahead for the ship to advance or to the outboard side for the ship’s stern to rotate around its pivot point.
A tug on the outboard side may reach a point of no return if it is unable to provide enough force to counteract the turn.
Does a ship propelled by a tug on the hip have a tendency to skid sideways?
- Yes, this is caused by the offset location of the propelling and steering forces.
Yes, a ship propelled by a tug on the hip does have a tendency to skid sideways.
When a larger ship is shifted, are more tugs required?
- Yes, the number of tugs required (unless stipulated by port regulations) will depend upon the size of the ship and the horsepower of the tugs.
Yes, more tugs are generally required when shifting a larger ship.
Are vessels ever handled stern first? Where should extra care be taken?
- Yes, but extra care should be taken when docking to avoid damaging the rudder and propeller
Yes, vessels can be handled stern first.
Describe several hookups for handling dead ships.
- With two tugs: a powerful tug aft on the hip to propel and a smaller tug forward for steering placed on either bow. With three tugs: a powerful tug aft on the hip with two smaller tugs forward on each side for steering, or two tugs aft with one tug forward for steering. With four tugs: two tugs forward and two aft on the hip for very large ships.
Several hookups for handling dead ships include:
* Towline connections
* Hip connections
* Stern connections
* Side connections.
Each hookup method may be chosen based on the specific situation and vessel characteristics.
Why is the use of a tug on a towline forward and a tug hipped up aft an effective way to use tugs?
- Because two moderately powered tugs can propel a sizeable vessel since both tugs are moving the ship. The forward tug can steer the vessel, and the after tug can back to check its way.
This is an efficient use of power especially for longer shifts.
This arrangement allows for enhanced control and maneuverability of the vessel.
How are tugs fast aft on beamy vessels used most effectively for steering?
- By using the tugs as if they were components of a twin-screw ship and by using their engines in opposition for steering effect.
Tugs fast aft on beamy vessels are used most effectively for steering by providing lateral thrust.
Why is an anchor called a poor man’s tugboat?
1, Because when a ves Theres is anchors, it can dispense with the services of a tue. There are also occasions when the use of the anchors is preferred.
An anchor is considered a poor man’s tugboat because it serves a similar purpose of holding a vessel in position without the cost of hiring a tug.
How does using an anchor differ from using a tug?
- The anchor is esse ules it assie” device that cannot push nor pull like a tug unless it has been “spotted” beforehand and is used as a “deadman” to heave against, or is used as a “brake” to check a vessel’s way.
Using an anchor relies on holding a vessel in place, while a tug actively maneuvers and positions a vessel.
What are the three functions of an anchor when a ship is maneuvering?
- Restrain but not stop the ship, fix or hold the anchored end of the ship, or provide a deadman to heave against.
- Holding the vessel in position
- Preventing drift
- Assisting in control during maneuvering
How is the anchor used when tugs are also employed?
The anchor is used to provide directional stability when the ship is lowed by the tug and to fix an end for the tug to turn the vessel.
The anchor can be used to assist in stabilizing the vessel while tugs maneuver it.
How are stern anchors used?
- Stern anchors may be used to keep ships from swinging with the tide, and are often used on passenger ships to hold up the sten of a vessel to provide a lee for the launches. When used with tugs they are often used in docking in fair tide situations.
Stern anchors are deployed from the aft of a vessel to provide additional holding power or control.
What is the danger when heaving a stern anchor?
- The possibility of the ship overriding the anchor and as a result doing damage to the rudder or propeller.
The danger when heaving a stern anchor includes the risk of the vessel swinging unpredictably or being damaged if not properly managed.
What are the two primary purposes of tugs in ship escort?
- Emergency Stopping
Emergency Steering
What are the three tug response modes?
- Retard
Assist
Oppose - 2 tugs, aft of the ship’s bridge
• 4. What is the least effective tug response position?
- Forward shoulder of ship
• 5. What is the most effective tug response position?
- Rudder tug tethered to ship’s stern
• 6. What are the three maneuvering options for a tethered ASD or tractor tug?
. Direct, indirect, in-line arrest
• 7. Why is ship speed critical to a ship escort response?
- Determines advance and carry
Compounds effect of time delay
Determines effectiveness of response positions
- What is the danger of the new line and winch technology used in ship escort?
- The line may not break or release if the tug is in peril
- What are the three qualities of good verbal communication?
- Simple, clear, easily understood not misunderstood
- Why did the verbal radio communication replace whistle signals?
2 More complex tugs and maneuvers required a bigger vocabulary than whistle signals could provide.
- What terminology must be clear for effective command and response communication?
- Communication that:
• Identifies the tugs
• Indicates the direction of force to be applied
• Indicates the amount of force to be applied
• Indicates the desired push or pull angle
• Verifies the receipt, understanding, and implementation of the command by the tug
- Why should the terms “full,” “on,” and “off” be avoided?
- They can be mistaken for other words
- How does the tug acknowledge an order?
- The tug operator’s response includes the tug’s name and repeating the order back to the pilot
- What is a means of non-verbal communication in shipwork?
- Action of the tug
Which statement is true about good communication?
A. It has no universal protocol or vocabulary
B. It has no universal principles
C. It must be verbal and spoken in English
D. All of the above
A. It has no universal protocol or vocabulary
It has universal principles that attempt to ensure an accurate exchange of information.
what do the following whistle signals mean by an assist tug?
1. One short blast if stopped
2. One short blast if you are going ahead or astern
3. Two short blasts
4. 3 very short blasts
5. One prolonged blast
6. One long blast followed by two short blasts
One short blast means “come ahead on your engines” if stopped.
One short blast means stop if you are going ahead or astern on your engines.
Two short blasts mean back your engine.
Three very short blasts is a signal for more speed.
One prolonged blast is a signal for slow speed.
One long blast followed by two short blasts is a signal to let go or shift the tug.
What statement is true concerning communication with the tug?
A. The tug should be identified first
B. Ambiguous words with multiple meanings should be avoided
C. Orders should be given as brief and direct as possible
D. All of the above
D. All of the above
Changing in pushing angles can be communicated with terminology that refers to the tug’s aspect to what?
The ship’s hull or other easily understood reference point
Tug response to a command must include what?
A. Tugs name and repeat order given
B. Tugs name only and “roger” or “affirmative”
C. just an affirmation of what was said “roger or affirmative” will do
D. None of the above
A. Tugs name and repeat the order given.
True or False: the type of towing mode is made to the pilot’s discretion.
True but it is collaborated with the tug captain.
