Seaman's Handbook

PART B. Steering and Sailing Rules : Action by stand-on vessel

(a)
  1. Where one of two vessels is to keep out of the way the other shall keep her course and
    speed;
  2. The latter vessel may however take action to avoid collision by her manoeuvre alone,
    as soon as it becomes apparent to her that the vessel required to keep out of the way is
    not taking appropriate action in compliance with these Rules.
(b) When, from any cause, the vessel required to keep her course and speed finds herself so close that collision cannot be avoided by the action of the give-way vessel alone, she shall take such action as will best aid to avoid collision.(c) A power-driven vessel which takes action in a crossing situation in accordance with subparagraph (a) (ii) of this rule to avoid collision with another power-driven vessel shall, if the circumstances at the case admit, not alter course to port for a vessel on her own port side.(d) This rule does not relieve the give-way vessel of her obligation to keep out of the way.