Action to avoid collision

Changing course or speed does not automatically end an encounter. Rule 8 connects action to Part B and to its result: passage at a safe distance, with effectiveness checked until the other vessel is finally past and clear. The drawing presents information states rather than a track to copy. Intention, action and outcome are different things. An apparent manoeuvre can still create another encounter, while a predicted passage needs subsequent observation. The rule therefore covers the quality and follow-through of action as well as its initial direction.

Rule 8(a), when circumstances admit, calls for positive action in ample time with regard to good seamanship. Paragraph (b) relates alterations to being readily apparent visually or by radar and says successive small alterations should be avoided. This establishes no minimum angle valid for every boat. An alteration’s significance depends on circumstances and the encounter. A degree checklist can look precise while teaching a rule that does not exist. Perceptibility matters because the other vessel also needs to appraise what is happening, not merely our private intention.