Shiphandling Flashcards
When turning in shallow water the diameter of the turn will ______ ? By how much?
<p>Increase. By twice the diameter.</p>
What happens to rate of turn in shallow water verses deep water?
<p>Remains constant, though turning circle (tactical) diameter increases in shallow water.</p>
Is transverse thrust while moving ahead more noticeable on a small or large ship
<p>Small, until almost no effect on ULCC and VLCC sized ships.</p>
If accelerating will turning circle diameter be larger or smaller than at constant RPMs.
Smaller. (Rule of thumb: Starting DIW with turns for 6 kts, turning circle will be 1/2 size of circle starting at 6 kts with constant RPM)
At what speed through the water does a bow thruster become effective?
Two knots.
At what depth do shallow water effects take place?
Depth of 1.2 to 1.4 of draft
In shallow water does ship become more directionally stable? Steering improves?
Yes
Does turning circle diameter increase or decrease with shallow water effects?
Increase
Does the ship twist more or less when backed in shallow water?
More
Does a ship carry further or shorter in shallow water?
Further
What direction from the wind does the bow tend when backing?
Bow falls away and ship will back into the wind. Due to pivot point moving aft.
As a ship reduces speed it will tend to turn in what direction relative to the wind?
It will turn into the wind.
What creates the pivot point?
The couple between the forward momentum of the vessel and the longitudinal resistance created by the water.
Where is the pivot point when the vessel is at a constant speed?
Approximately 1/4 of the ships length from the bow.
How does the pivot point location effect turning levers?
The moment of force times the length to the pivot point creates the turning lever.
How does the excessive use of astern bells effectively put a ship ‘out of control’?
Leaves the ship exposed to transverse thrust, wind, tide, and bank or shallow water effect.
How can loss of rudder control be overcome at slow speeds?
By using the ‘Kick Ahead’ or ‘Pumping the Rudder’ technique.
When using the ‘Kick Ahead’ or ‘Pumping the Rudder’ technique what is important to keep in mind about rudder position?
Insure rudder is hard over to prevent unwanted increases in ahead motion.
Which is more effective for ‘pumping the rudder’ or a ‘kick ahead’? A steam ship or a diesel ship?
A diesel ship because it comes up to speed faster.
What safety should be used with a turbine plant?
Leave dead slow ahead as long as possible because plant can be slow to come on line.
What creates transverse thrust?
- Helical discharge on the port side of the rudder. 2. Upward flow from the hull puts more pressure on the downward sweeping blades.
What direction does a right hand prop move the bow when rotating ahead?
Port
What direction does a left hand prop move the bow when turning ahead?
starboard
What direction does a right hand prop move the stern when turning astern?
Port
What direction does a left hand prop move the stern when turning astern?
Starboard
When turning ahead what direction does a right hand prop turn when viewed from astern?
Clockwise
When turning ahead what direction does a left handed propeller turn when viewed from astern?
Counter clockwise
What percentage of applied power will be transverse thrust?
5-10%
What is the wedge effect?
The movement of water, from astern wheel wash, down between the ship and a solid face acting as a cushion. By backing you create a water wedge between the pier face and the vessel.
In what direction is does the transverse thrust of a left handed controllable pitch propeller move the stern when backing?
To port like a right handed fixed propeller.
Does transverse thrust increase or decrease when shrouded by a nozzle?
Decrease
Where is the pivot point when dead in the water.
At center of underwater mass, approximately amidships depending on trim.
Where is pivot point when initially moving ahead?
1/8 the ship length from the bow.
Where is pivot point while turning when moving ahead at a constant speed?
1/3 of ships length from the bow.
What is the type resistance which develops a ship to moving bodily sideways through the water?
Lateral Resistance
Why are turning circles at different speeds approximately the same diameter?
- Because lateral resistance and rudder force find a balance. 2. Only the rate of turn changes 3. Speed entering a turn does not increase the turning ability.
How much of a speed reduction can be expected in a turn with constant RPMs? Why?
30-50% loss, due to the increase of lateral resistance due to the increase of exposed side shell.
At what RPM is the minimum radius achieved in a standing turn?
Dead in the water to dead slow ahead
What are the three different directional stability conditions?
- Stable - Steadies up when rudder is put amidships 2. Neutral - Continues a swing at a steady rate with rudder amidships 3. Negative - Swings at increasing rate with rudder amidships
