The first right-of-way rule that most of us learned is that port-tack boats keep clear of starboard-tack boats (currently rule 10). There are, however, exceptions – that is, situations where starboard-tack boats have to give room to port-tack boats. This month I will look at the exception created by the rule governing mark-room, rule 18.
(click on the diagram to see a larger cleaner version)
In the diagram, the blue boat on port tack gets to the zone (3 lengths from the mark) clear ahead of yellow, on starboard tack. Blue and yellow are required to leave the mark on the same side, and blue is about to enter the zone at position one, so according to rule 18.1,, rule 18 applies between them (the rest of 18.1 lists exceptions that don’t apply here, but will be discussed next month). Rule 18.2(b) says that if a boat is clear ahead when she reaches the zone – as blue is – a boat clear astern at that moment – yellow – shall thereafter give her mark-room, which is room for blue to sail to the mark and then sail her proper course when she is at the mark. At position 3, yellow forces blue to alter course away from the mark. This means that she is not giving blue room to sail to the mark. Here, blue breaks rule 10 since as port-tack boat, she is not allowing yellow to sail her course. Rule 18.5 exonerates blue for breaking that rule, though, since yellow was not giving blue the mark-room to which she is entitled. Even as a starboard-tack boat, yellow cannot sail the course that she wants to because she is required to give blue the room needed to sail to the mark. (Blue, on the other hand has no obligation to allow yellow to sail to the mark, so yellow must sheer off.)
10 ON OPPOSITE TACKS
When boats are on opposite tacks, a port-tack boat shall keep clear of a starboard-tack boat.
18 MARK-ROOM
18.1 When Rule 18 Applies
Rule 18 applies between boats when they are required to leave a mark on the same side and at least one of them is in the zone. …
18.2 Giving Mark-Room
(b) If boats are overlapped when the first of them reaches the zone, the outside boat at that moment shall thereafter give the inside boat mark-room. If a boat is clear ahead when she reaches the zone, the boat clear astern at that moment shall thereafter give her mark-room.
18.5 Exoneration
When a boat is taking mark-room to which she is entitled, she shall be exonerated if, as a result of the other boat failing to give her mark-room, she breaks a rule of Section A, …
Mark-Room
Room for a boat to sail to the mark, and then room to sail her proper course while at the mark. However, mark-room does not include room to tack unless the boat is overlapped to windward and on the inside of the boat required to give mark-room.
(click on the diagram to see a larger cleaner version)
The second diagram shows a slightly simpler, but less common situation that only happens with a leeward mark that is to be left to starboard, which may happen around a gatemark and in match racing. The green boat is on starboard, while the red boat is on port. As they get to the zone they are clearly overlapped so rule 18.2(b) entitles red to mark-room. Although red is entitled to sail to the mark, she is still port-tack boat and is thus not entitled to hold the course seen at position 1 or 2, which might give her a better gybing angle. As with yellow in our first example, and despite being the starboard-tack right-of-way boat, green must give mark-room to the port-tack boat,
Next month, we will look at why this is all true at a leeward mark but not at a windward mark.
© Copyright 2011 Andrew Alberti