Case 24
Definition, Room
Rule 11, On the Same Tack, Overlapped
Rule 12, On the Same Tack, Not Overlapped
Rule 15, Acquiring Right of Way
Rule 21(a), Exoneration
When a boat becomes overlapped to leeward from clear astern, the other boat must act promptly to keep clear. When she cannot do so in a seamanlike way, she has not been given room as required by rule 15.
Facts
Two boats, A and B, are on a broad reach on starboard tack in a light breeze on their proper courses for the next mark some distance away. Initially, B is clear astern of and directly behind A but is travelling slightly faster and becomes overlapped close to leeward of A's stern.

Questions
  1. When are B's obligations under rule 12 replaced by her rights as leeward boat under rule 11?
  2. What are B's obligations under rule 15?
  3. 3. What are A's obligations under rule 11?

Answers
  1. As soon as B becomes overlapped, rule 12 ceases to apply. A becomes bound by rule 11, and B by rule 15.
  2. Rule 15 embodies the principle in the rules that when the right of way shifts from one boat to another, the boat with the newly acquired right of way must give the other boat space and time for response and thus a fair opportunity to keep clear. B's obligation under rule 15 is not a continuing one; it protects A only temporarily, and only if she responds promptly after the overlap begins (see the definition Room).
  3. Rule 11 requires A to keep clear and, if this requires her to luff, she must do so promptly. If A does so but some part of her hull, crew or equipment touches any part of B's hull, crew or equipment, A breaks rule 11. If the contact occurred despite A having luffed in a seamanlike way, B has broken rule 15 by not giving A room to keep clear and A is exonerated under rule 21(a) for her breach of rule 11. However, if A luffed higher than is necessary to keep clear of B and, as a result, causes contact with B, A has been given the room required by rule 15 and is not exonerated.