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Tacking on a mark, room to keep clear?
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Rupert View Drop Down
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Posts: 8956 		Post Options Post Options   Quote Rupert Quote  Post ReplyReply Direct Link To This Post Topic: Tacking on a mark, room to keep clear?
    Posted: 02 Jun 19 at 5:11pm
I really like the last point of certainty principle. It is one of the clearest concepts for dealing with complex situations. It might not get the answer right, as such, but in this case, where both boats may genuinely believe they are in the right, as we could be talking a couple of degrees of course change, it ensures clarity of decision making.
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ohFFsake View Drop Down
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Posts: 219 		Post Options Post Options   Quote ohFFsake Quote  Post ReplyReply Direct Link To This Post Posted: 02 Jun 19 at 10:56am
As ever, the confused, muddied waters made crystal clear by Brass!
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Posts: 1143 		Post Options Post Options   Quote Brass Quote  Post ReplyReply Direct Link To This Post Posted: 30 May 19 at 1:22pm
Originally posted by ohFFsake

One other practical point to add to the mix...

Presuming we are all now agreed that A [(Y)ellow] is grant mark room to B until the instant she passes head to wind, at which point rule 18 switches off in its entirety.

From this moment on, B must now keep clear of A(Y) (Rule 13), but this presumes that A maintains her current course.

 If A alters course towards B then she is a ROW boat and must allow B room to keep clear (Rule 16.1)

A situation I have encountered several times is where two boats end up in this scenario, B heads up to the mark and A follows, but then A continues to alter course once B commences her tack, subsequently blaming B if there is then an incident.

Summarising:

  • B passes head to wind, mark-room entitlement ceases and B becomes required to keep clear of A (Yellow),
  • If Yellow hits B, or takes action to avoid contact because she needed to, B breaks rule 13, with no exoneration in sight.
  • If Yellow changes course, other than as needed to avoid B, she is required to give B room to keep clear, and:
-  if Y hits B, B is exonerated from breaking rule 10 in accordance with rule 21 because she is sailing within the room to which she is entitled, and Y breaks rule 16.1 and 14.
-  if Y takes action to avoid contact with B because she needs to, Y has given B room to keep clear but B has failed to keep clear and, again, breaks rule 13.

My understanding from the above is that the instant B reaches head to wind, A cannot then continue to alter course if doing so would prevent B from keeping clear.

Please don't bring back the 'prevent' language from 1992, but yes.

 Or in practical terms if A chooses to follow B around the mark once they have tacked they must now in effect keep clear.

'In effect' nothing.  B is required to keep clear, Y is required to give B room to keep clear.

The only scenario in which B would be to blame if there were an incident would be if A remained on a steady course from the instant that B passed head to wind.

Or if Y took action that she needed to take to avoid B.

Originally posted by Sam.Spoons

I think that is the point, they are approaching the mark and when B tacks yellow (A?) will hit blue either just before head to wind or just after unless she bears away under her stern.

And if it goes to a protest hearing, the protest committee should apply the principle of last point of certainty:  up to and including when B reaches head to wind (Definition:  Leeward and Windward), B was on starboard tack, entitled to mark-room.

She remains in that status until it is clear or certain that she has passed head to wind.

Hitting B is high risk for Y.

Y is better to take action to avoid B and protest.
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Posts: 3370 		Post Options Post Options   Quote Sam.Spoons Quote  Post ReplyReply Direct Link To This Post Posted: 30 May 19 at 10:24am
I think that is the point, they are approaching the mark and when B tacks yellow (A?) will hit blue either just before head to wind or just after unless she bears away under her stern.
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Posts: 219 		Post Options Post Options   Quote ohFFsake Quote  Post ReplyReply Direct Link To This Post Posted: 30 May 19 at 9:32am
One other practical point to add to the mix...

Presuming we are all now agreed that A is grant mark room to B until the instant she passes head to wind, at which point rule 18 switches off in its entirety.

From this moment on, B must now keep clear of A (Rule 13), but this presumes that A maintains her current course. If A alters course towards B then she is a ROW boat and must allow B room to keep clear (Rule 16.1)

A situation I have encountered several times is where two boats end up in this scenario, B heads up to the mark and A follows, but then A continues to alter course once B commences her tack, subsequently blaming B if there is then an incident.

My understanding from the above is that the instant B reaches head to wind, A cannot then continue to alter course if doing so would prevent B from keeping clear. Or in practical terms if A chooses to follow B around the mark once they have tacked they must now in effect keep clear. The only scenario in which B would be to blame if there were an incident would be if A remained on a steady course from the instant that B passed head to wind.
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Brass View Drop Down
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Posts: 1143 		Post Options Post Options   Quote Brass Quote  Post ReplyReply Direct Link To This Post Posted: 24 May 19 at 2:35pm
Originally posted by mozzy

So i guess you'd start with a basic rule that covers all situations of:
"However, it does not apply between boats on opposite tacks"

But that alone would be too broad and would include boats on opposite tacks downwind (opposite 'gybe') and have unintended consequences for leeward / gybe marks. 

So they add 'on a beat to windward' to avoid the above.   

But adding that leaves a grey area for reaching legs that are ended with a tack. As these are not really a beat to windward, but you do end up with boats on opposite tacks at the mark. So they add 18.1 b) 'between boats on opposite tacks when the proper course at the mark for one but not both of them is to tack'... which covers the tiny instance after you've tacked to fetch around a mark you have reached toward on the opposite tack. But also seems to have a lot of duplicity with 18.1 a).

In the real world I see no reason why a boat clear ahead and on the same approach tack shouldn't be given room to round the mark ahead / inside, even if that includes a tack.

Without thinking too hard about it, I think a reason why is that while gybing is instantaneous (and all the stuff about mainsail filling in MR has just been put back there to maintain the pre 1995 status quo), tacking involves a significant change in speed and manoeuverability, which runs contrary to the 'orderliness' imposed by crystallising entitlements at the zone boundary.

But finding a way to word that without giving mark room to port tack approaches is hard.  I think some of the difficulty comes from 'tack' the verb not being defined. 

If the verb was defined as the time between head to wind and close hauled (as implied by rule 13), and room was given for that 'tacking' then you'd escape this ridiculous situation where a boat first entitled to mark room then right of way is the keep clear boat for 45 degrees of turn, despite that turn being completely predictable by all boats around. 

The definition of 'tacking' was removed from the rules in the 1995 rewrite.

If you wanted to convey the meaning you seek, then, in the few places it would be required you could say 'a boat, having passed head to wind but not yet reached a close hauled course'.

Generally, despite the habits of drafters to define labels for every damn phrase, unless a phrase is used frequently, that is, more than three or four times in a document, it is better not to create a defined term, but use the phrase when needed.
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Posts: 1143 		Post Options Post Options   Quote Brass Quote  Post ReplyReply Direct Link To This Post Posted: 24 May 19 at 2:25pm
Originally posted by GML

Originally posted by Brass

Could you elaborate a bit please?
I assume you mean me Brass...

The question as I understood it was why bother with RRS18.1(a) when RRS18.1(b) would seem to do the same job. My point was that whilst that may be true at a windward mark, it may not be true at a mark on a beat that is not a windward mark - the most obvious example being a finish mark, but other examples include a passing mark on an upwind leg and a gate halfway up a beat (for example where boats have to pass through the start/finish line on each lap). In that case RRS18.1(a) still applies, but RRS18.1(b) may not, as neither boat may need to tack at the mark to sail their proper course - they may be able to just keep sailing upwind on the same tack.

So in the following example I believe RRS18.1(a) applies but RRS18.1(b) does not (assuming this is the finish line):



Thanks, great, very helpful.
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Post Options Post Options   Quote Guests Quote  Post ReplyReply Direct Link To This Post Posted: 24 May 19 at 2:07pm
So i guess you'd start with a basic rule that covers all situations of:
"However, it does not apply between boats on opposite tacks"

But that alone would be too broad and would include boats on opposite tacks downwind (opposite 'gybe') and have unintended consequences for leeward / gybe marks. 

So they add 'on a beat to windward' to avoid the above.   

But adding that leaves a grey area for reaching legs that are ended with a tack. As these are not really a beat to windward, but you do end up with boats on opposite tacks at the mark. So they add 18.1 b) 'between boats on opposite tacks when the proper course at the mark for one but not both of them is to tack'... which covers the tiny instance after you've tacked to fetch around a mark you have reached toward on the opposite tack. But also seems to have a lot of duplicity with 18.1 a).

In the real world I see no reason why a boat clear ahead and on the same approach tack shouldn't be given room to round the mark ahead / inside, even if that includes a tack. But finding a way to word that without giving mark room to port tack approaches is hard.  I think some of the difficulty comes from 'tack' the verb not being defined. 

If the verb was defined as the time between head to wind and close hauled (as implied by rule 13), and room was given for that 'tacking' then you'd escape this ridiculous situation where a boat first entitled to mark room then right of way is the keep clear boat for 45 degrees of turn, despite that turn being completely predictable by all boats around.  
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GML View Drop Down
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Posts: 94 		Post Options Post Options   Quote GML Quote  Post ReplyReply Direct Link To This Post Posted: 24 May 19 at 1:12pm
Originally posted by Brass

Could you elaborate a bit please?
I assume you mean me Brass...

The question as I understood it was why bother with RRS18.1(a) when RRS18.1(b) would seem to do the same job. My point was that whilst that may be true at a windward mark, it may not be true at a mark on a beat that is not a windward mark - the most obvious example being a finish mark, but other examples include a passing mark on an upwind leg and a gate halfway up a beat (for example where boats have to pass through the start/finish line on each lap). In that case RRS18.1(a) still applies, but RRS18.1(b) may not, as neither boat may need to tack at the mark to sail their proper course - they may be able to just keep sailing upwind on the same tack.

So in the following example I believe RRS18.1(a) applies but RRS18.1(b) does not (assuming this is the finish line):
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Brass View Drop Down
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Posts: 1143 		Post Options Post Options   Quote Brass Quote  Post ReplyReply Direct Link To This Post Posted: 24 May 19 at 9:44am
Could you elaborate a bit please?
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