CASE 15
Definitions, Mark-Room
Rule 12, On the Same Tack, Not Overlapped
Rule 13, While Tacking
Rule 18.1(b), Mark-Room: When Rule 18 Applies
Rule 18.2(b), Mark-Room: Giving Mark-Room
Rule 18.2(d), Mark-Room: Giving Mark-Room
In tacking to round a mark, a boat clear ahead must comply
with rule 13; a boat clear astern is entitled to hold her course
and thereby prevent the other from tacking.
Facts
A and B are approaching the windward mark which they are required to
leave to port. They are close-hauled on parallel courses with A clear ahead.
A expects B, when she can tack and fetch the mark, to tack to round it and
head for the next mark. Instead, B holds her course as shown in the diagram
and sails on well past the mark.
Question
Has B the right to hold her course in this way and, thereby, prevent A from
tacking?
Answer
Yes. While A remains on port tack, B is required to keep clear by rule 12
and, as A was clear ahead when she reached the zone, B is required by rule
18.2(b) to give A mark-room as well. Provided B keeps clear of A and gives
A mark-room if A luffs (even if A luffs as high as head to wind), B is entitled
to sail any course she chooses, including holding her course. However, B is
no longer required to give A mark-room after A leaves the zone (see rule
18.2(d)).
The mark-room to which A is entitled does not include room for her tack
(see the last sentence of the definition Mark-Room). If A were to pass head
to wind, then at that moment all parts of rule 18 would cease to apply
because the boats would be on opposite tacks on a beat to windward (see
rule 18.1(a) and Case 132). In addition, A would no longer have right of
way under rule 12, and B would become the right-of-way boat under rule
13.
GBR 1966/8