Ch. 11 Flashcards
Define a tug’s assist lever.
The distance between the location of the tugs applied force and the ships pivot point.
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 which can easily overpower the tug.
What are the three means a tug has to apply force when working alongside?
Push, act as a drogue, or pull on the line
What are the four factors that affect a tugs effectiveness when working alongside?
Angle of the tug, offset position of the tug, drag force, and the tugs applied horsepower
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 tug allocates almost all its horsepower to maintain position at or close to 90 degrees. There is minimal lateral pull applied to the tugs headline. The tugs angle, offset position, drag, and horsepower are all working on a long assist lever to counter the turn.
In breasted towing, a tug made up on the ships stern creates, in effect, a ________ship.
twin screw
In breasted towing a tug made up on the bow acts as a _______.
Steerable bow thruster
What is negative water flow?
Negative water flow is when the tugs wash opposes the general direction of the water flowing by its hull.
How is negative water flow a factor in conventional tug performance?
Negative water 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 tugs engine, clutch, or couplings.
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 both equal forces to both starboard and port. The tug can enhance the effect of the ships rudder on a ship with headway and can also control the bow and steer a ship with sternway.
What precautions should a 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.
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 5 knots or less, and indirect towing at higher speeds
What is the essence of effectively using tugs to steer and propel ships
Steering and propelling ships with tugs is a matter of using the tug force as an affective lever in conjunction with the ships maneuvering lever.
