Stand-On and Give-Way Obligations

Rule 16 requires every vessel directed to keep out of the way, so far as possible, to take early and substantial action to keep well clear. The manoeuvre must meet Rule 8 and remain understandable to the stand-on vessel; a token course change followed by uncertainty does not discharge the duty.

Under Rule 17(a)(i), the stand-on vessel initially keeps course and speed, preserving a predictable reference for the give-way vessel. Rule 17(a)(ii) then says she may take avoiding action by her manoeuvre alone as soon as it becomes apparent that the vessel required to keep out of the way is not taking appropriate action.

Rule 17(b) is the later must-act stage: when the vessels are so close that collision cannot be avoided by the give-way vessel's action alone, the stand-on vessel shall take the action that will best aid collision avoidance. For two power-driven vessels in a crossing situation, a stand-on vessel acting under 17(a)(ii) should, if circumstances admit, not alter to port for a vessel on her own port side.

The boundary is judgement, not a fixed distance. Repeated bearings, range, closure, sea room and the other vessel's apparent action must be monitored continuously. Sound or light warning signals and speed reduction may be relevant, but none replaces the manoeuvre required to avoid collision.