The Rules Guy: Mark Room – When Do You Have to Gybe?

SinC Mark Room Gybe Alberti 400

Jun 1, 2022

by Andrew Alberti

I have now written three articles about mark-room at a gybe mark. Last time, we talked about situations when you were allowed room to gybe. I finished off showing a case where you are required to gybe. The situations in my earlier articles occur most commonly when boats have been sailing a reach or upwind course to the mark and the next course is downwind. This time we will look at marks where boats have been sailing downwind and the next course is upwind. Generally, these are called leeward marks.



















In the diagram, Green and Red are both approaching a leeward mark to be left to port. Green is on starboard tack and Red is on port tack. As they arrive at the zone, Green is overlapped inside Red, so entitled to mark-room. Green is also right-of-way boat since she is on starboard tack. Red not only has to give mark-room, she has to keep clear. There is a restriction on Green’s course. Green has to gybe to sail her proper course, so according to rule 18.4, Green cannot sail further from the mark than her proper course before she gybes. In this diagram, Green sails further from the mark than she has to, but no further than her proper course. If Red was not there, then Green would probably sail “wide and close” to position herself right beside the mark as she heads upwind. This is therefore Green’s proper course. If she had sailed further from the mark, she would have broken rule 18.4. If Red had forced Green closer to the mark by not keeping clear, then Red would have broken rule 10. After she gybes, Green is the windward boat, so required to keep clear, but she Red still has to give her mark-room. gif maker


Rule 18.4 does not apply at gate marks. Gate marks are a pair of leeward marks between which the boats must pass before heading up around outside either one of them. The situation in the second diagram looks very similar to the first diagram, but since this time it is a gate mark, there are additional considerations. Yellow, the starboard-tack boat is not limited by rule 18.4 and so does not have to gybe. Blue originally thinks that Yellow will gybe but eventually discovers that she has to gybe herself to keep clear. Blue would have been well advised to go to the other gate mark earlier on. Yellow has to be careful of aggressive tactics like this, since another boat might further complicate the situation by coming in from behind.

Since the presence of a gate mark instead of a single mark may have profound implications for the fleet’s conduct at marks, boats are well advised to become familiar with the SI’s early in race preparations rather than when approaching the zone.


Mark-Room Room for a boat to leave a mark on the required side. Also,

(a) room to sail to the mark when her proper course is to sail close to it, and

(b) room to round or pass the mark as necessary to sail the course without touching the mark.

However, mark-room for a boat does not include room to tack unless she is overlapped inside and to windward of the boat required to give mark-room and she would be fetching the mark after her tack.

Proper Course A course a boat would choose in order to sail the course and finish as soon as possible in the absence of the other boats referred to in the rule using the term. A boat has no proper course before her starting signal.

Zone The area around a mark within a distance of three hull lengths of the boat nearer to it. A boat is in the zone when any part of her hull is in the zone.


When boats are on opposite tacks, a port-tack boat shall keep clear of a starboard-tack boat.


When boats are on the same tack and overlapped, a windward boat shall keep clear of a leeward boat.


18.1 When Rule 18 Applies

18.2 Giving Mark-Room

(a) When boats are overlapped the outside boat shall give the inside boat mark-room, unless rule 18.2(b) applies.

(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.

18.4 Gybing

When an inside overlapped right-of-way boat must gybe at a mark to sail her proper course, until she gybes she shall sail no farther from the mark than needed to sail that course. Rule 18.4 does not apply at a gate mark.


Copies of these rules articles along with animated diagrams can be found at > sailing > programs > KnowRules.


Andrew Alberti 400Andrew Alberti is an International Judge and National Umpire. He is a member of the Sail Canada Rules and Appeals Committees. Send your questions to Andrew at









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