Wednesday, 30 May 2012

Does Rule 17 apply?

During a Medal Race at the Delta Lloyd Regatta a three boat situation near the finish developed involving rule 17. Let me start by the 'classic' situation where the middle boat has a rule 17 limitation and the leeward boat has not.

Two boats overlapped with red as leeward boat encounter a third (grey) boat. Purple establishes an overlap to leeward of Grey within two boat lengths and has a rule 17 limitation. Red however does not have the same limitation. She has an overlap with Grey (because Purple in the middle has an overlap with both), but not within two boat lengths, so Red does not have a rule 17 limitation.
Grey must keep clear as windward boat, but Purple may not sail above her proper course. Because Purple has to keep clear of Red her proper course is to luff when Red luffs. She does not sail above her proper course, because she would have done the same, if Grey wasn't there and she must keep clear of Red.

With me so far?

Now almost the same situation.

In this the overlap was long standing on the downwind, without a rule 17 limitation. Red is within two boat lengths of Grey. Grey manages to get clear ahead and breaks the overlap. A few seconds later the overlap is re-establish.

My question to you: does Red have to Gybe immediately? In other words, does rule 17 now apply for Red?

And what if we added a fourth boat overlapped to leeward of Red?



  1. Rule 17 says a boat shall not sail above her proper course. In this case the middle boat's proper course is to fulfill her obligation to keep clear of a RoW leeward boat.
    She is not breaking 17.

  2. The middle boat is not breaking 17, but Red would if she did not gybe immediately. She establishes leeward overlap from clear astern within two hull lengths of Grey. 17 applies.

    Add another leeward to Red. If the new boat (say blue) is also within two hull lengths of Grey etc, then 17 applies. If not, then we're back to the first case with Red being another middle boat.

  3. Yes but there is the matter of red being overlapped with grey. Red is so overlapped on account of being overlapped with the purple boat between them. In both instances, the key overlap was established from clear astern. The other germane part of rule 17 is 'becomes overlapped within two of her hull lengths to leeward'. I think if red is more than two hull lengths to leeward of grey when the overlap is formed, then she can sail above her proper course. Purple is sailing her proper course when she luffs to keep clear of red.

    Two hull lengths to leeward is not a lot when there is an intermediate boat. In the first diagram, red is almost (but not quite) two hull lengths away


  4. Yes Red has to gybe immediately.

    As soon as the overlap is broken, Red is clear astern of Grey (even though Red is still overlapped with Purple). As soon as Purple becomes re-overlapped with Grey, Red becomes (re-)overlapped with Grey (because Purple is between them and overlapped with both). On the facts stated, this happens when Red is within two of her hull lengths to leeward of Grey (and they are on the same tack). Rule 17 therefore applies and Red shall not sail above her proper course while they (Grey and Red) remain on the same tack. Red's proper course in this case is to immediately bear away and gybe (whilst complying with rule 16).

    If there was a fourth boat to leeward of Red then in my view it is unlikely that that boat would be within 2 hull lengths to leeward of Grey at the moment the overlap was re-establised, in which case rule 17 would NOT apply to that boat. She would therefore not be required to gybe immediately and Red's proper course would, as in your first example Jos, be to comply with rule 11 and keep clear of that fourth boat.

  5. I had written a long post, but I lost it.

    Anyway, I see nothing in the wording of 17 that results in red not needing to gybe immediately in this situation. I don't see how fact there is a boat in between her and grey changes anything.

    And if there's a fourth boat to leeward of red, well, to return to the wording: 17 ON THE SAME TACK; PROPER COURSE
    If a boat clear astern becomes overlapped within two of her hull
    lengths to leeward of a boat on the same tack, she shall not sail above her proper course while they remain on the same tack and overlapped within that distance, unless in doing so she promptly sails astern of the other boat.

    So the question is: what is the distance between grey and the fourth boat? > 2bl to leeward = the fourth boat not constrained by 17.
    < 2bl = 4th boat must not sail above proper course.

  6. To contradict myself, as Murray Walker might have said, Red's proper course could be to luff purple. That might reasonably be the course she would sail to finish as soon as possible in the absence of grey.


    1. Wag, I disagree: note that proper course is "to finish as soon as possible", not "to finish in the best position possible."

      Luffing Purple may defend Red's position, but it is not her proper course.

    2. Latindane, I did have as soon as, rather than best position, in mind. That is why I said it might reasonably be the course she would sail. Being in front is usually the quickest way to the finish, especially in fleet racing.

      It does not need to be the quickest, it needs to be reasonable for red to think it might be the quickest.



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