Ch. 7 Flashcards
What is the critical decision point?
A point in a maneuvering sequence that requires a critical action at a specific time
Describe the effect of propeller torque on a conventional single-screw tugs with a right handed propeller.
A “Right hand propeller” will have a tendency to move the stern to starboard and the bow to port when engaged ahead. When reversed it will move the stern to port and the bow will fall off to starboard.
How is a single screw tug maneuvered when it is necessary to back for some distance?
It is steered when moving astern by giving an occasional kick ahead on the engine to correct the heading. This is done briefly enough so it does not destroy the sternway.
How is a single screw tug turned in a short distance?
It is turned by “backing and filling” alternately going ahead and astern on the engine with the helm turned toward the direction of the turn.
Will a single screw tug turn more readily in one direction than the other?
Usually it will since the stern will be cast to one side or the other when the tug backs its engine. This will be to port with the standard right hand propeller. Tugs with nozzles may not react the same way.
What is the principal advantage of flanking rudders or a steerable nozzle rudder on a single screw tug?
They enable a single-screw tug to steer astern and maintain position when backing during shipwork.
Are steerable nozzles as effective as flanking rudders?
No, because when the tug is backing and filling to make a tight turn, the nozzle angle must be reversed between the ahead and astern engine maneuvers.
How does a twin screw tug steer with engines?
Both propellers thrusting in the same direction with the same RPM will balance each others torque and off center position. By manipulating the balance between the two engines, a twin screw tug can steer with its engines.
What is meant by the term twin screwing?
That the tug is being maneuvered with one engine ahead and one engine astern. The tug can be turned completely about without moving ahead or astern.
What is meant by the term flanking and how is it done?
Flanking means moving a tug laterally by using its engines and rudders in opposition. For example, if the port engine ahead stbd engine astern rudder to port the tug will move to starboard.
How do conventional tugs usually undock?
By coming ahead on a springline until the stern is open then backing clear of the dock. However a twin screw tug may flank off of the dock.
How does a conventional tug dock?
It will usually approach the dock at an angle of 15 to 20 degrees, stop its engine, then bear off and back its engine when close alongside. It can the be worked ahead on a springline until it is in position.
What do the wheel and pitch levers control on a VSP tractor tug?
The wheel controls the bow and pitch levers control the stern. The pitch levers also control fore and aft movement of the tug.
A tractor tug will steer ______ a turn.
Into
What two methods can be used to bring a VSP tractor tug to a stop?
One is by using the pitch levers alone (reversing pitch), the other is a combination of pitch levers and wheel (turning the tug 90 degrees to its original heading).
