What the examiner is probing
At Master level the examiner is not testing textbook definitions of turning circles. They want evidence that you, as the person legally and operationally responsible, understand the forces acting on your vessel, can predict and manage her behaviour in confined and open water, and can articulate the decisions you would make before and during a manoeuvre. A pass answer names the forces, explains how vessel characteristics and environmental factors modify them, and demonstrates that you have a pre-planned response, not a reactive one.
The underlying knowledge
Forces governing manoeuvring
- Pivot point — stationary vessel: roughly amidships. Vessel moving ahead: moves forward (approximately one-third from bow). Vessel moving astern: moves aft. Knowing pivot point position tells you where the bow or stern will swing in response to rudder.
- Transverse thrust (paddlewheel effect) — most pronounced at low speed and when going astern. A fixed right-handed propeller going astern kicks the stern to port. At Master level you must state how you exploit or counteract this; e.g., use it to assist a stern-to berth on the port quarter, but account for it when departing.
- Propeller wash over rudder — rudder only generates significant force when water flows across it. Ahead, the propeller accelerates flow; astern, the rudder is largely ineffective until the vessel gathers sternway through undisturbed water.
- Interaction — in shallow or confined water, squat increases with speed (bow squat in fine-form vessels, even-keel squat in full-form). Bank cushion pushes the bow away from a nearby bank; bank suction draws the stern toward it. Passing vessel interaction causes similar pressure differentials.
Restricted water considerations
- Reduce speed early. Squat and interaction forces are speed-dependent; halving speed dramatically reduces both.
- Tidal stream and current: if the stream is favourable, maintain steerage-way relative to the bottom whilst keeping ground speed manageable. Manoeuvre with the tide under the bow where possible to maintain rudder authority.
- Turning short round: identify whether wind, stream or transverse thrust dominates. Use the dominant force to assist the turn; hold it with engine or thruster rather than fight it.
- Anchor-assisted turning: in very confined water, use the anchor as a pivot, letting the cable take the load whilst the propeller drives the stern around.
Open water
- Advance and transfer: know your vessel's tactical diameter. A large motor yacht may carry significant way after engines astern are ordered.
- Emergency stop: the stopping distance at full sea speed can be several vessel lengths. As Master you must know this from sea trials data or the pilot card and communicate it when briefing harbour masters or pilots.
Structuring your spoken answer
State the dominant forces relevant to the scenario first. Then explain how vessel characteristics (propeller handedness, hull form, draught) and external factors (wind, stream, depth) modify those forces. Finish with the manoeuvre sequence: what you order first, how you confirm it is working, and what your abort criteria are. This moves you from knowledge to command decision, which is where the pass mark is awarded.