Ship Handling and Manoeuvring
What the ship handling paper tests
Turning circles, pivot point, squat, interaction and bank effect, tug and anchor work, and berthing judgements in wind and current. Questions are usually situational: what happens next, and why.
Core rules
- Pivot point is roughly one-quarter of the length from the bow when making headway, and about one-quarter from the stern when going astern. The ship turns about that point, not the centre.
- Advance is the distance run in the original direction to the point where the ship has turned 90 degrees; transfer is the sideways distance. Both grow with speed and displacement.
- Squat increases with speed squared and with block coefficient, and is roughly doubled in confined or shallow water. A useful approximation in open water: squat (m) = Cb x V squared / 100, with V in knots.
- Bank effect: the bow is pushed away from a nearby bank and the stern drawn toward it, with a suction force that peaks in shallow, narrow channels.
- Transverse thrust: a right-handed propeller kicks the stern to starboard when going ahead and to port when going astern, strongest at high power and low speed.
- Anchoring: pay out a scope of about 5 to 7 times the depth, more in heavy weather, and let the cable veer rather than snubbing it.
Worked example
Cb 0.80, speed 8 kn in open water: squat = 0.80 x 64 / 100 = 0.51 m. The same ship at 8 kn in a confined channel could expect about 1.0 m. If under-keel clearance was 1.2 m, the margin is gone in the channel and speed must be cut to about 5 kn, giving 0.20 m open water, around 0.40 m confined.
Traps that cost marks
- Assuming the pivot point stays at the same place when the engine is put astern.
- Forgetting that squat rises with the square of speed, not linearly.
- Treating bank suction as symmetric for bow and stern.
- Planning a turn without allowing for advance, the most common error in collision-avoidance turning plans.