Thursday, 4 March 2010

Looking for 18.1(b) again!

The discussion in the comments of the original search for rule 18.2(b) made me realise something peculiar.
Well, at least I find it peculiar. You can tell me otherwise in the comments, as usual.

Rule 18 is divided in five rules numbered 18.1 trough 18.5 and some of them even further divided into parts by using letters (a), (b), (c) etc. It makes it a very complex rule. It was worse in the previous rulebook were obstructions were also part of rule 18. But it is still one rule, with me so far?

The rule starts with giving us the exceptions - when rule 18 NOT applies, of which 18.1(b) is one of them.

On a side note: Uli came up with the only  logical place on the race course (so far) where rule 18.2(b) 18.1(b)  is the only rule switching off rule 18. In all other places we have to twist and turn to get to it. He stated:
Example 3:
Mark 2 on a trapezoid course.
Only 18.1(b) but not 18.1(a) apply between a port boat coming form mark 3 and a starboard boat coming from mark 1.

But back to my original point.

Although we agree it is a complex rule and written extremely well for it's purpose, there is, in my opinion, a logic flaw. If rule 18 is switched off within rule 18 itself (by part 18.1) how can rule 18 tell us that it is switched off? It is no longer applicable. If it's not applicable it can't be used, and if it can't be used it can't tell us it is switched off!

I'm sure that the writers have considered this, but I can't help thinking: "this is a circular reference, like we sometimes get in excel"

What do you think?



  1. I am reminded of the t', as in "trouble at t' mill". The t' is silent, but its still there.

    Wag, who comes from Yorkshire.

  2. It reminds me of when my 4-year-old granddaughter says, "It's Opposite Day," which means that today she means the opposite of everything she says.

    I always tell her that she can't say that. Because if she says, "It's Opposite Day," then she really means, "It's NOT Opposite Day." But then if it's NOT Opposite Day, she shouldn't say it IS Opposite Day.

    She's very smart for a 4-year-old but she always looks at me very strangely when we have this conversation. Circular references seem be beyond the understanding of 4-year-old girls and the writers of the RRS.

  3. Dear Jos;
    I always appreciate your great work in LTW.
    Page 159 of the Understanding the Racing Rules of Sailing by Dave Perry;
    If you have the book, please look at it. There is a diagram.

    WI and LO, close-hauled on port tack and overlapped, were approaching the windward mark. When WI reached one and half boat lengths from the mark, WI began tacking to starboard. LO continued to sail without changing course. There was contact between the stern right edge of WI and the gunwale left side of LO.

    Dave Perry's explanation; (copy)
    LO must give WI mark-room under rule 18.2, which includes room to tack. However, the moment WI passes head to wind, she and LO are on opposite tacks and rule 18 shut off. At that point rule 13 requires WI to keep clear of LO while tacking; and rule 14 always requires both boats to avoid contact. If the boats touch the moment after WI passes head to wind, both boats could be penalized: LO for not providing enough space a moment sooner when the boats were on the same tack; and WI for failing to keep clear of, and hitting, a right-of-way boat.

    My opinion, which is "opposite" against Dave's.
    As both WI and LO overlapped when WI reached the zone, rule 18 applies. LO is required by rule 18.2(b) to give WI mark-room. As WI is overlapped to windward and on the inside, mark-room includes room to tack under the definition of mark-room. LO broke rule 18.2(b). WI is exonerated under rule 18.5(a) for breaking rule 13.
    (Please refer to Month's Quiz )

    1. Dave regards the second sentence of rule 18.2(c) as important.
    2. I would like to regard to the definition of mark-room as important.
    3. Which one will take priority, rule 18.2(c) or the definition of mark-room?
    4. In case of this situation, when will rule 18 switch-on and switch-off ?
    sen Yamaoka

  4. Hm,

    isnt it like a computer program, which is interpreted line by line?
    If rule 18 is a function of that program that is called, the function may switch off itself based on a condition that is checked within the function.

    It is pretty much like the question "Do you really want to continue? (Yes/No)" (for example in the function "delete").
    Depending on the answer the rest of the function remains unexecuted (or here: inapplicable) in that incident, but the functinon may be called again in another incident.
    However, to get the function to ask you whether you want to continue or not, the function has to be called.

    Best regards,


  5. @Wag, Thanks from J - who likes to go to Yorkshire;

    @Tillerman, I thought I was bad confusing people with my thinking, but you do it even to a four year old;

    @Sen, valid points indeed. I'll have to think about the answer before I can give you one. Perhaps even make separate post about it?;

    @Thorsten, Good analogy, I'm going to use it in presentations, thanks!
    Nevertheless I think it would be better not to make the rules more difficult then they already are...

  6. She is a very smart 4-year-old. Her father is a lawyer. I think it's good for her intellectual development to introduce her to logical paradoxes at an early age. For now she just says, "Grandad is silly," but she will appreciate what I am doing one day.

    Her 20 month old brother said, "Grandad silly." for the first time yesterday too. He may be right.

  7. Dear Sen, dear Jos,

    regarding the rules situation in Dave Perry's book, question 2 of Q&A 2009-17 might provide an answer. Please see

    Referring to question number 3 in Sen's post, the definition of mark-room takes precedence over rule 18.2(c).

    I like this outcome. It makes sense to me.

    If, in contrast, the green boat were not exonerated, it would lead to a situation in which the red boat not giving mark-room causes a penalty for both.

    Nevertheless, in the Q&A, it is rule 18.5(b) and not 18.5(a) which leads to Green's exoneration. But I guess this is rather a minor issue.

    best regards,
    Martin Clasen

  8. I've changed the 18.2(b) into 18.1(b) with strike-trough in the original post.


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