Saturday, 25 September 2010

LTW Readers Q&A: Mark-room in ISAF MR Call 2010-004

Dear Jos,

Would you care to publish the following?

Rapid Response Match Racing Call 2010-004 has just been published.


It deals with a boat (Yellow), having rounded the windward mark well ahead and having completed a penalty just outside the zone, now on starboard, approaching Blue who is just finishing rounding the mark on port.
The Call asks and answers the question: ‘Does rule 18 apply between Yellow and Blue?’

Unsurprisingly it answers that rule 18, rule 18.2(a) to be precise, does apply.
I would have thought that this would have been painfully obvious. There are two boats. They are required to leave a mark on the same side. At least one of them is in the zone. None of the exemptions shown in rule 18.1 apply. Of course rule 18 applies.

Of much more interest is what happens when an instant after the last position in the diagram in the Call, when Blue leaves the mark astern and is no longer at the mark.

The instant Blue ceases to be at the mark, she is no longer taking mark-room to which she is entitled (to sail her proper course at the mark), and thus she ceases to be entitled to exoneration for breaking rule 10. Blue instantaneously switches from being a boat entitled to exoneration for breaking rule 10 to being fully obliged to keep clear by rule 10, without even the protection of rule 15.

So, to extend the problem diagrammed in the Call, just after Position 4, Yellow luffs, and makes non-damage contact between Y’s port bow and B’s port quarter.

Yellow Y Flags.

What is the umpire’s decision?


Calls only answer a specific question. This one is no exception.

The situation described is so specific that it will only happen once out of a hundred. But it can happen. As long as Blue is not yet past the mark she needs protection from a starboard boat. She entitled to protection under rule 18 . Like you stated, shortly after that she has passed the mark and she no longer needs protection and now can gybe to keep clear. She must do that as keep clear boat. She already can anticipate having to do this while rounding the mark because she's always keep clear boat.
The same is just before Yellow has turned down below ninety degrees. Then she is still on a beat and so there is no overlap, therefore rule eighteen does not apply. Only in those few moments between Yellow turning downwind and Blue passing the mark, rule 18 is in effect. And that is exactly when she needs it.

To answer your call, after Blue has passed the mark and there’s contact
  • If Blue did everything to keep clear, Yellow broke 16.1; Penalize Yellow
  • If Blue did nothing or not enough to keep clear, she broke rule 10; Penelize Blue.


  1. The 'what happens next' part of this exposes an anomaly in the rules in the way they distinguish between mark room and right of way. If blue is to do everything she can to keep clear, she needs to start doing it at position 3. Just after 4, her mark room switches off. Yellow acquired right of way between position 2 and 3. She held her course from position 3, the collision course arose from blue's action, so rules 15 and 16 are not germane to yellow's action. I think, according to the rules, blue has to keep clear. She should not have gone there.

    I also think that is unsatisfactory. Having taken her mark room, blue should be entitled to room to keep clear.


  2. JOs,

    My intention in describing "just after Position 4, Yellow luffs, and makes non-damage contact between Y’s port bow and B’s port quarter" was to indicate that Yellow luffed in an attempt to avoid contact when it was clear that Blue was not keeping clear.

    Surely a change in course for the sole purpose of avoiding contact, and which is away from the contact does not expose Yellow to rule 16?


    I don't agree that Blue needs to begin keeping clear @3: from @3 to just after @4, Blue is taking mark-room to which is entitled and will be exonerated if she does not keep clear.

    I disagree that Yellow acquired right of way because of Blue's actions. As you correctly observe Yellow acquired right of way between @2 and @3 _when Yellow tacked from port to starboard_ . Yellow acquired right of way through her own action in tacking. Rule 15 applies @3, but I think Yellow has discharged her obligation to initally allow room to keep clear by the time she reaches @4.

    On the one hand I can understand Jos' argument that Blue had all the time from when Yellow acquired right of way @3 to anticipate and prepart to meet her obligation to keep clear when rule 18.5 shut off, but I am inclined to agree with you that Blue deserves some sort of rule 15-like protection.

  3. Blue needs to decide at position 3 whether she can safely sail her proper course around the mark, so mark room is effectively given or denied at that moment.

    Would you all accept the following logic?

    While determining that Blue had options to keep clear after Yellow's tack, we notice that none of these options permit Blue to sail her proper course while at the mark.

    Thus Yellow's tack and subsequent steady course required Blue to begin keeping clear while 18.2a still applied. The requirement to keep clear deprived Blue of mark-room, so Yellow broke rule 18.2a. Exonerate Blue under 18.5b.

  4. Can we say that this example is analagous to Case 30?

    The instant before B loses her rule 18.5 exoneration for breaking rule 10, Y broke rule 18.2(a): Penalise Y.

    On the instant B lost her rule 18.5 exoneration, she broke rule 10.

    Y's breach of rule 18.2(a) compelled B to break rule 10 after she had lost her rule 18.5 exoneration: Exonerate B.

    If Y had given B sufficient mark-room then B would have been able to keep clear of Y.

  5. At position 4 does Blue not have room to gybe and pass the mark without hitting it?
    in a matchrace situation she has a proper course on either gybe and as a keep clear boat I do not think she deserves the right to choose.
    This should be a Blue penalty. I agree with comments above that neither 15 or 16 have any application here. Rule 18 is still a mess for match racing.

  6. From Case 30, the message seems to be:
    Ask not what rules applied at the moment the boats (would have) collided; ask what rules applied at the moment a rule was broken.

    So, Brass, I think I see how your example is analagous. Rule 18.2a applied when Blue would have had to leave her proper course around the mark, in order to keep clear of Yellow, so Yellow failed to give room and broke 18.2a. Just like rule 12 applied in Case 30 when the boat ahead should have started action to avoid a collision.

    I do not understand the concept of 18.5 shutting off. In When a boat is taking mark-room ... she shall be exonerated... the word 'when' seems to identify the situations to which exoneration can apply, not to limit the time during which infringements are covered. The later parts of that rule exonerate infringements that are a direct result of taking mark room, not just infringements that occur while taking mark room.

  7. O'Hara,

    I think your first paragraph is nicely put.

    As to 'when' rule 18.5 'shuts off', the content of 'when' comes from the definition of mark-room: '... to sail her proper course while at the mark ...'. The instant a boat ceases to be _at_ the mark, she is no longer 'taking mark-room to which she is entitled', so the condition in rule 18.5 is no longer fulfilled.

    The same logic would apply if 'when' was changed to 'if': the condition in rule 18.5 is 'taking mark-room to which she is entitled'. It is the amount of room to which the boat is entitled, not whether or not she has a hypothetical entitlement to mark-room (that is, not whether rule 18 applies).


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