Collision Regulations and Watchkeeping
Rules that must be automatic
You must know the steering and sailing rules by heart: the obligation to keep a proper lookout by all available means, safe speed, and the risk of collision assessment. Understand the difference between a vessel not under command, a vessel restricted in her ability to manoeuvre, and a vessel constrained by her draught. Know the crossing, head-on and overtaking rules, and the meaning of a give-way and stand-on vessel. Understand the conduct of the stand-on vessel: hold course and speed, but act when collision cannot be avoided by the give-way vessel alone.
Traps
A common trap is applying the crossing rule to a vessel approaching from dead ahead; that is a head-on situation. Another is assuming the stand-on vessel may alter to port at any time; early action to port in a crossing situation is discouraged. Watch for questions on the meaning of 'in sight', which requires visual sighting, not radar alone. Also be careful with narrow channels, traffic separation schemes and the meaning of a 'close-quarters situation'.
Worked rule of thumb
For a crossing situation, use the mnemonic: if the other vessel is on your starboard side and showing her red light, you are the give-way vessel and should alter to starboard and pass astern. Example: a power-driven vessel sees a red light fine on her starboard bow; she must give way, preferably by a bold alteration to starboard. If the bearing remains constant and the range decreases, a risk of collision exists; take early and substantial action and make it evident.