-Rounding weather mark Boat A & Boat B
-Boat B clear astern prior to the zone (no overlap)
-lead boat A leaves room for boat astern to dive in between mark and herself still within the zone. ie Boat B takes the room.

How soon can Boat B start to luff Boat A???

Boat B has to give boat A room to sail her proper course until they are past the mark and overlap is broken.

Breaking an overlap before a mark doesn't get rid of mark room.

Going past the mark doesn't get rid of the fact that Boat B is an overtaking vessel within 2 boat lengths and therefore cant go above her proper course.

Since the first boat to reach the zone was clear ahead, Rule 18.2(b) applies. Boat B must give Boat A mark room, and since an overlap was established after Boat A entered the zone, B is also subject to rule 18.2.(c).

18.2(c) When a boat is required to give mark-room by rule 18.2(b),
(1) she shall continue to do so even if later an overlap is
broken or a new overlap begins;
(2) if she becomes overlapped inside the boat entitled to
mark-room, she shall also give that boat room to sail her
proper course while they remain overlapped.

Mark-room - Room for a boat to leave a mark on the required side. Also,
(a) room to sail to the mark when her proper course is to sail close to it, and
(b) room to round the mark as necessary to sail the course.

Proper Course - A course a boat would sail to finish as soon as possible in the absence of the other boats referred to in the rule using the term.

Room - The space a boat needs in the existing conditions, including space to comply with her obligations under the rules of Part 2 and rule 31, while manoeuvring promptly in a seamanlike way.

Therefore, Boat A is entitled to sail their proper course until the overlap is broken.

In practical terms, B can't luff A until the overlap is broken, then re-established. A can sail her proper course, which may be directly to the next mark, or her optimal downwind angle (but she can't jibe, unless that is her proper course to the next mark). It's a very low percentage maneuver for B - until the overlap is broken. If I'm A, I'm going to try to pin B to the mark then say the magic word.

Agree with most of that. Rule 17 is also critical to some of the points made above.

Matt, in your "practical" paragraph, how would re-establshing overlap help B, in light of RRS 17? The only difference I see is that if the overlap is established under 18.2(c), the limit on B is A's proper course; while if it is established under 17, the limit on B is B's proper course. Not sure that I can think of a good example of where that matters, other than maybe at the far gybing lay line?

Mike

Mike - if they are still subject to 18.2(c) then A gets to determine proper course. If B breaks the overlap, then re-establishes it, yes, they are subject to 17, but then they get to sail their proper course.

May not make much of a difference in one-design, but it sure makes a difference in dissimilar boats, especially if one (A) carries a symmetrical chute and another (B) carries an asymmetric.

Okay next question..

How long are you considered to be rounding the mark???

I don't think it's about that anymore. A left the door open at the mark and as long as B can get through there and A can't close the door at any point while rounding that mark, B has assumed and taken the inside position legally....that's pretty much the end of the story as it relates to "mark room".

With regards to luffing, it's an overtaking / proper course situation that is completely independent from the mark rounding isn't it?

Thanks Matt, that confirms what I thought.

Tom, the answer is, until she is no longer rounding the mark. I believe there are cases, or calls published on this if you have time to look them up before I do.

Jake, the rounding matters for the reasons Matt and I mentioned. RRS 18 modifies whose proper course dictates L's options.

Mike

When your course is no longer influenced by the proximity of the mark. Basically, once you've passed it.