November/December 2017 - What to watch for when you are going leeward II

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November/December 2017 - What to watch for when you are going leeward II

Last month, I looked at two boats going downwind towards the leeward mark and the requirement to look to leeward for boats coming upwind. This month I want to talk about looking astern. I have commonly heard reference to a rule, “overtaking boats must keep clear.” This rule is actually not in the rulebook (though something close is in Colregs, governing boats not racing, but that’s outside the scope of this article). It is a good shortcut to remember rule 12, but there are some important differences.

In the diagram, four boats, Yellow, Gray, Green and Pink, are astern of – and overtaking – four other boats Blue, White, Red and Light Green. At a glance similar, their situations are actually very different. The end of rule 12 says, “a boat clear astern shall keep clear of a boat clear ahead.” but note that the first part of the rule also adds a qualifier, “When boats are on the same tack and not overlapped”, so Yellow must keep clear of Blue, as they are on the same tack, just as Gray must keep clear of White – both of these pairs of boats are on the same tack. Green and Red are not on the same tack, nor are Pink and Light Green, so rule 12 does not apply. Moreover, Green and Light Green are both on starboard, so we go back to rule 10. The port-tack boats (Red and Pink) must keep clear of the starboard-tack boats (Green and Light Green).
The lesson here is that if you are on port tack going downwind, you have to pay attention to the boats behind you – a starboard-tack boat could be a problem and it may be very difficult for Red to get out of the way. Green is obligated to avoid a collision, but she is right-of-way and Red would have to take a penalty if Green is forced to take avoiding action.
The second difference between “overtaking boats must keep clear” and the real rule 12 is illustrated in the second diagram. At position 1, Yellow is clear astern of Blue and must keep clear. Yellow is sailing faster so at postion 2, they are overlapped. Since rule 12 only applies when they are not overlapped, rule 11 now applies. Blue as windward boat must keep clear of the leeward boat, Yellow. As Yellow has just acquired right of way, rule 15 requires that intially she shall give Blue room to keep clear. By position 3, Blue should have started to do something. At postion 4 when the boats make contact, it is clear that Blue has done nothing and has broken rule 11.
The message is that  being ahead is not a signal to relax your guard. There may be boats behind as well as beside and in front of you, any one of which may turn your relaxing run into chaos.

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.
When boats are on the same tack and not overlapped, a boat clear astern shall keep clear of a boat clear ahead.
When a boat acquires right of way, she shall initially give the other boat room to keep clear, unless she acquires right of way because of the other boat’s actions.

© Copyright 2017 Andrew Alberti
Posted: 4/29/2019 11:14:54 AM by Andrew Alberti | with 0 comments

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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
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