Sunday, 30 August 2009

Change in the Definition of Obstruction?


By Rob Overton

The Section C Working Party, consisting of Ben Altman, Chris Atkins, Dick Rose, Richard Thompson and myself, have made two submissions to ISAF that deal with rules 18 and (indirectly) 19. One is an "emergency" change in the definition of Obstruction, to go into effect January 1, 2010, and the other is a proposed ISAF Case dealing with the meaning of Room.

Before we get into the submissions themselves, let's look at the perceived problem. There are a number of scenarios in which Rule 18, Mark-Room, and Rule 19, Room to Pass an Obstruction, appear to conflict. Consider the following scenario, taken from a team-race call suggested by Matt Knowles. The boats are at a reach mark to be followed by a run:

Black is clear ahead of both Grey and White when she enters the zone, and Grey is inside White when they the zone. Grey and White are sailing faster than Black. Grey sails to pass to leeward of Black, and White elects to sail between Grey and Black. In doing so, White forces Black to luff up. Black protests White under rule 18.2(b) for not being given mark-room, and White protests Grey under rule 19 for not giving her room to pass to leeward of Black.

White's argument is that Black is an obstruction to both Grey and White because they both owe Black mark-room (see definition 'Obstruction'). So when Grey elects to go to leeward of Black, she must give White room to do so, too. By sailing up toward White between positions 1 and 2, Grey fails to give White room, causing White to sail too close to Black and thus forcing Black above her course to the mark. White admits she broke rule 18.2(b) with respect to Black but claims she was compelled to do so. She points out that when it became clear that Grey was not going to give her room under rule 19, she could not avoid both Black and Grey. So that means Grey should be disqualified, and White exonerated under rule 64.1(c) for her breach of rule 18.2(b).

Grey sees it a different way. White is required to give mark-room to both Grey and Black, and from positions 1 through 3 that means giving them room to sail to the mark. White could easily have seen that she would not be able to go between Black and Grey and still give mark-room to both of them, so she wasn't "compelled" to break rule 18.2(b). Therefore White should not be exonerated. Grey says she herself broke no rule; she was entitled to room under rule 18.2(b) and was simply taking the room to which she was entitled.

(Note that Grey can insure she is blameless by bearing off toward the wrong side of the mark to give White room to pass between her and Black, and protesting White. Now White has clearly broken rule 18.2(b) by not giving Grey room to sail to the mark, and Grey has given room as required by rule 19.)

This apparent conflict between rules 18 and 19 is caused at least in part by the fact that Black is an obstruction to both White and Grey. This is because the definition of Obstruction says a boat racing is an obstruction only if they both "required to keep clear of her, give her room or mark-room or, if rule 22 applies, avoid her." If those words " give her room or mark-room" were removed, then White's case disappears. Black would only be an obstruction as long as both Grey and White are clear astern of her, and after that, Grey would be under no obligation to give White room to pass to leeward of Black.

This is the substance of the submission the Section C Working Party has put forward to ISAF. The definition Mark-Room would say "… However, a boat racing is not an obstruction to other boats unless they are required to keep clear of her or, if rule 22 applies, avoid her. …"

But wait; think about the following scenario:

Under the current definition, PW is an obstruction to both PL and SW because, even though she has right of way over neither of them, they both owe her room to pass Yellow. This means that SW must give PL room to pass between her and PW. Under the proposed definition, neither PL nor PW would be obstructions to SW. SW would still be required to give PL and PW room to pass SL because SL has right of way over all those boats; but why should SW give PL room to avoid PW?

The answer is a basic principle, not explicitly stated in the Racing Rules of Sailing, but nonetheless clearly implied: It is not seamanlike to break the rules. Because SW owes PL room to pass between her and SL, and because PL cannot do that without giving room to PW, thus SW must give PL room to give PW room.

Because this is not explicit in the rules, nor in the ISAF Cases, the Section C Working Group has proposed a new ISAF Case that makes this principle explicit.

So how does this pair of submissions solve problems as in the first example above? Well, under the proposed new definition of Obstruction Black would not be an obstruction to either Grey or White, so rule 19 does not apply. End of problem.

Before making these submissions, the working group spent a lot of time thinking of scenarios where the change to the definition of Obstruction might cause problems. Despite our efforts, we could think of none. Can you think of any place on the racecourse where the words "give her room or mark-room" are necessary in the definition of Obstruction? If you can, please let me know by commenting on this blogsite or contacting any of the members of the Section C Working Party. E-mail addresses for Ben Altman, Dick Rose and I are on the US SAILING website, at

I've copied the text from the doc in it's entirety. If you can answer Rob's question, don't hesitate to do so!


  1. I see no aparant conflict, as basic principles play a role here too. Black has right to mark room from both white and grey, grey committed to giving white room to do so to leeward. Until
    grey aquired right to mark-room herself, when white can't give both mark-room.

    The answer is just like with the proposed definition of obstruction: a basic principle, not explicitly stated in the Racing Rules of Sailing, but nonetheless clearly implied:

    It is not seamanlike to break the rules.

    Because grey and white owe black mark-room, and because grey cannot do that without giving room to white, thus grey must give white room to give black room.

    With the proposal black would be no longer an obstruction after she became overlapped, yet white, must stay clear of grey..and both must give black mark-room, grey cannot give black mark-room without giving white room to do so..

    I don't see a difference with or without the change in the definition of obstruction. What am I missing?

  2. Theo, The concept of 'seamanlike' arises only in the definition of room. With Rob Overton's proposed change, the only room Grey owes to White is room to keep clear if Grey changes course, per 16.1. So the proposed change does change something: it ensures that Grey may legally sail a steady course to the mark, assuming he stays behind Black.

    But maybe Grey cannot even hold course, because you said that Grey cannot give Black room without giving room to White. Presumably you consider that Grey forcing White into Black's room has the same effect as Grey directly sailing into Black's room, so either action by Grey violates the rule. I tried (in desperation) that kind of logic in LTW QA24 but no-one else used this logic, and I now think it was poor logic. Grey, if he holds course, owes no room to White; Grey can rely on White to follow the rules, unless and until Grey/White contact is imminent; that is the end of Grey's concern with White. Grey left room for Black, but White stole that room.

    We want the rules to mean "White may not force his way in if he has late overlap" without exceptions, and I think the proposal is an attempt to close an arguable exception. I agree it is not a very big change.

    I like the emphasis of the principle that "room" includes room to follow the rules. This principle gives a simple reason why the outside boat must give lots of room in a crowded leeward mark rounding, as considered at LTW QA24. Each boat owes the boat just inside her room to round legally, which includes room to give any boat just inside him room to round legally, which includes...

  3. Surely Grey owes Black mark-room as she was clear astern of Black when Black entered the zone. Black is denied her entitlement to mark-room simply by Grey and Whites presence between Black and the mark preventing Black to sail to the mark. White and Grey both broke rule 18.2(b).

    If Grey had an inside overlap when Black entered the zone and White was clear astern of Grey at that moment, then only White breaks 18.2(b). Grey breaks no rule because Black is not an obstruction to Grey. Phil.


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