November 2014 - How Much Mark-Room

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November 2014 - How Much Mark-Room

This month’s article is based on another question I received from a reader. The question asked about mark-room – in particular, mark-room with large booms. The boats in my diagrams tend to have very long booms and sometimes they exaggerate the real situation. Most booms don’t go far past the side of the boat. There are exceptions, though; some boats have boom that extend well beyond the rail when the boats are on a run. 8 Metres and Nonsuches come to mind. Both types have large mainsails, and so are also more likely to sail directly downwind on a run with their booms fully extended. 

In the diagram, the two boats are approaching a leeward mark which they will round to port. Yellow is on a run on starboard-tack. Blue is on broad reach on port-tack. As Yellow gets to the zone, the boats are overlapped so Yellow is entitled to 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 the mark as necessary to sail the course.

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.

The space a boat needs in the existing conditions, including space to comply with her obligations under the rules of Part 2 and rule 31, while manoeuvring promptly in a seamanlike way.

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.
18.4 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.

Yellow’s proper course will require her to gybe at the mark. She is therefore required by rule 18.4 to gybe no farther from the mark than needed to sail her proper course. This is pretty close to the mark. Blue is required to give Yellow mark-room, which is “room to round the mark”. Room is defined as “The space a boat needs in the existing conditions,”…“while manoeuvring promptly in a seamanlike way.” This calls for some judgement on Blue’s part. As Yellow’s seamanlike gybe would include letting the boom go out on the starboard side, Blue must quickly calculate the space required – which obviously would be greater than if Yellow were a boat with a short boom – and then stay far enough away to keep clear once Yellow’s boom is fully extended.

A similar situations would occur if Yellow had to douse a spinnaker. Blue has to allow space for Yellow to do a seamanlike takedown. Blue does not, however, have to allow space for Yellow to do a sloppy takedown (even though it might be in her best interests to do so). An ISAF Case is based on a question about a boat that is short-handed and has an inexperienced crew. The answer says that the outside boat (in our case, Blue) has to allow room for “the boat handling that can be reasonably expected from competent, but not expert, crew of the appropriate number for the boat.”
ISAF Case 103 Answer 1
Neither the experience of IW’s crew nor their number is relevant in determining ‘room’. In rule 19.2(b), which requires OL to give IW ‘room’ between her and the obstruction, ‘room’ is a defined term. The definition Room is ‘the space a boat needs in the existing conditions . . . while manoeuvring promptly in a seamanlike way’. In determining whether or not OL has given the required space, the interpretation of ‘seamanlike way’ must be based on the boat-handling that can reasonably be expected from a competent, but not expert, crew of the appropriate number for the boat.

Good practice and safety would dictate that if the outside boat sees that the inside boat is inexperienced and/or short-handed, they should allow some extra room, but this is not required. On the other side, a short-handed and/or inexperienced crew might consider going on the outside if they have a complicated manoeuver such as a spinnaker takedown.

© Copyright 2014 Andrew Alberti
Posted: 11/1/2014 11:08:52 AM by Andrew Alberti

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This page provides links to a set of articles original published in Kwasind magazine. The versions here include animated diagrams. The original articles can be found within the original magazines which are available online back to January 2007. 

Articles before December 2016 are based on the Racing Rules of Sailing 2009-12 or 2013-2016 and have not been updated to reflect the changes that apply as of January 2017 with the publication of the Racing Rules of Sailing 2017-20. A copy of the new rules can be found on
Andrew Alberti has been writing these monthly articles in the Kwasind since early 1997.  They explain the Racing Rules of Sailing. Andrew is a National Judge and National Umpire. He is a member of the Sail Canada Rules and Appeals Committees. The interpretation of the rules contained in the articles is Andrew's and not that of the RCYC or any of the committees he sits on. 

Send your questions to Andrew at


166 Years of Tradition | World-Class Sailing | Toronto Island & City Clubhouse
Sailing Rules: Mark Room - When Can You Gybe?
Mark Room at a Gybe Mark
Penalties – When and How to Take Them
New Rule Changes III
Mark Room at a Gybe Mark
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