Vessel Motion Flashcards
Lateral motion is easier to detect from which position on the bridge?
Centerline
Where is the pivot point of a vessel with lateral motion but no rotational motion?
At the Center of Lateral Resistance (CLR)
Jeff 220
A ship’s maneuvering lever is defined by the relationship of what two forces?
Pivot Point and the ship’s propulsion forces
Jeff 220
As a stopped ship gains turning momentum (tug or thruster force), what is the result in the ship’s longitudinal motion?
Begins to creep ahead.
Jeff 254
A ship stopped, puts rudder hard over and ahead on engines. Where is the initial PP?
Within 1/8 L from bow.
Jeff 257
What is the drift angle of a ship turning?
The angle in relation to the ship’s centerline and direction in which the ship’s bridge is actually traveling in a turn.
Jeff 259
Drift angle for full-bodied ships such as bulkers is _________ than the drift angle for ships with finer, narrow hulls.
Larger
Jeff 261
A ship is stopped and PP is at the CLR (close to midship). If a tug starts pushing on bow or stern to create rotation on the ship, what happens to the PP?
It shifts towards the end of the ship, opposite from the tug.
Jeff 252
When conducting a turning circle, which is larger?
A. Tactical diameter
B. Final diameter
A. Tactical diameter
House 38
When a vessel has a list, making a turn in the direction towards the angle of list, the turn will be:
a. Smaller, and quicker
b. Larger, and quicker
c. Smaller and take longer
d. Larger and take longer
d. It will take longer and result in a larger turn
House 42
When a vessel is moving ahead, the transverse thrust:
A. Considerable, moving the stern in the direction of propeller rotation
B. Minimal, therefore this negligible effect is generally ignored.
B
House 43
Define the term “headreach.”
The distance travelled forward over the ground, after engines are stopped
House 223
The aim in berthing larger vessels is generally to obtain a singular lateral motion, in order to land parallel to the dock, and also, because lateral motion is easier to check than ______ motion.
Rotational
Hooyer 12
As a rule of thumb on a loaded ship at full ahead on an even keel, in slack water, start reducing speed about ____ times the ship’s length, from the position in which you’d start maneuvering.
20x
Williamson 3
As a rule of thumb on light ship at full ahead on an even keel, in slack water, start reducing speed about ____ times the ship’s length, from the position in which you’d start maneuvering.
10x
Williamson 3
Normally a ship’s speed will need to be below what speed before starting engines astern?
5 kts
Will 3
It’s best to reduce speed gradually, through each bell, in order to maintain control. This is particularly important with which type of propeller?
CPP
Will 4
A ship travels 100 feet in one minute at 1.0 knot. This is equivalent to _____ nm/min.
0.017 nm
Will 4
A ship with a right-hand turning propeller turns “short round” best when turning which way?
To starboard
Will 9
The majority of CPP props are ____-hand turning.
Left
Will 10
Pivot point for a vessel stopped is located where?
At the center of gravity. Will be midships for a vessel on an even keel. Further aft if trimmed by the stern.
The “wind force moment” is the resultant moment from multiplying _____ x ______.
Wind force lever by the wind’s force
Will 26
A vessel will settle in a “neutral position” when stopped, as wind and current forces are balanced. The ship will tend to return to these positions after moving away from them. For most vessels, the three neutral positions are:
A vessel stopped
A vessel moving forward, into the wind
A vessel moving astern, sailing with a tailwind
Herve 111
Two “unstable neutral positions” for most vessels, which a vessel will tend to move away from, are:
Moving forward, with a tailwind
Moving astern, with a headwind
Herve 111
What is the most effective method of slowing a vessel?
Drifting or turning
Herve 131
How does vessel’s speed relate to the resistance of air and water as their forces affect a ship’s motion?
The square of relative ship speed
Herve 132
For most vessels, an accelerating turning circle diameter (starting from a stop) is less than _____ of that for a turning circle at constant speed while underway.
Half
Mac 11
Any ship significantly trimmed by the head will have what kind of directional stability?
Negative.
Mac 19
Large, full-bodied ships with large block coefficients often squat to increase trim in which direction?
By the head
Mac 19
Which force is more strongly felt by a vessel, bank cushion or bank suction?
Bank suction
Mac 21
If a vessel in a narrow channel starts to sheer due to bank suction/cushion, what should be done?
Do not reduce speed! Let the head fall off towards mid-channel, and maintain some rudder towards the near bank while increasing RPM. Once heading starts a few degrees back towards center of channel, increase rudder to check swing
Mac 47
When making a turn in a channel, begin the turn when what point on the ship is at the turning point at the end of the reach?
Abeam the pivot point.
Mac 74
