Which takes precedence - 18 or 19?

I think you can be as certain as possible that you picked the option that lost you the least time...

I just tried drawing it... I get two options. In one OW can spin round in PLs wake and fetch the mark. In that case IW can probably spin round and fetch the mark too, most likely clear astern of OW. I think in that case IW has to carry on sailing past the mark and let OW round first.
However the other option is when OW cannot spin round and make the mark but has to sail past it. At that point it gets so complicated and hypothetical I give up, because they are probably going to end up either tacking in the zone or leaving the zone and R18 will turn off at some unpredictable stage. Up until that stage I think its hard for IW to end up with a requirement to take a penalty, provided they gave room to get past the stern, and very easy for OW to end up with one...

Getting a bit lost in the A,B,C so I will use labels from Case book

Port tack leeward = PL = C
Inside Windward = IW = B (inside boat at the mark)
Outside Windward = OW = A (outside boat at the mark)

I have been thinking about this:

There seems to be a Catch 22 situation, due to the fact that two boats are simultaneously bound by 2 different rules, and the definition of room means that any rights they may have includes each have obligations to give the other boat room to conform to a rule.

 Rule 19 obliges IW (B) to give room to OW (A) to pass astern of PL (C). This room includes room for OW(A) to "meet her obligations under the rules of Part  2 and rule 31 (see definition). OW (A) has an obligation to give IW (B) mark-room under rule 18.2b

So IW(B) must give OW(A) room to pass astern of PL(C) AND room to give  IW(B) mark room! However, because OW(A) must give IW(B) mark room she must also give IW(B) room to meet her obligation to give OW(A) room to pass the obstruction.....

Now try to draw the course each boat must sail meet their obligations.

OW (A) bailing out does simplify life.

Gordon

Originally posted by Presuming Ed If windward, by taking room at the obstruction, cannot give mark room AND/OR leeward can only get round the mark by not giving room at the obstruction, then AFAICS the only way for both boats to avoid the obstruction and round the mark without either breaking 18 or 19 is for leeward to luff and take both boats across the bows of the obstructing boat.  (Ceteris Paribus - i.e. both would claim that they the other broke 18/19 if one/both goes behind the boat beating).

Originally posted by deadrock Difficult to assess without timings and distances, but 'room and opportunity' (R&O) may come in to play here. If boat C has tacked soon after the mark, boat B has to start taking avoiding action only once boat C has completed her tack. I know we are talking about big boats here, not Lasers (and no, we don't have paint on a Laser) but boat B may have seen the incident developing a fraction before boat A. B is obliged to give room to boat A, even if no hail is made, but if boat C has given B only just enough R&O to get round C's stern, there may not have been enough R&O for B to give A room as well. Additionally Boat B may have had little option but to bear off round C's stern, if the alternative was a sharp luff that would have endangered A &/or C.