Right of way with three or more boats

Originally posted by NickA As for my second example (not to scale - the boats came out too big!).  Taking Brass's advice on treating the matter as two pairs of boats.    A (red) has already tacked and B (blue) has tacked in response in order to keep clear - fine

Read rule 20 again.  B's obligation is to tack (or hail 'You tack') in response to A's hail.  If A tacks before B responds, then A probably breaks rule 20.

Secondly, B's rule 20 obligation is to give A room to tack and avoid her, not to keep clear.

But so be it:  A and B have both tacked onto PORT and and are now approaching C on STBD.

Once on PORT, B has no entitlement whatsoever to hail C for room.  Rule 20 only gives a boat an entitlement to hail a boat on the same tack.

At the second position in your diagram, A and B are purely in Case 11 territory:  two boats on Port approaching a boat on starboard.  B may elect to duck C, in which case she must give A room to do likewise, or B may give A a rule 20 hail for room to tack away from C, and A must respond.

If B uses rule 20 to tack away from C and A tacks, then, A will be entitled to give another rule 20 hail to B (because of the original obstruction), who must then respond, but by then, C will be out of the way and they can both get on with their race.

Well it's a matter of choice for B, but it is not a problem for C, who is the right of way boat, subject only to the rule 16.1 limitation that if she changes course she must give A and B room to keep clear of her.

See above.  C certainly had no obligation to tack.  It was up to A and B to keep clear of C.  Going head to wind and slowing is a perfectly seamanlike way for B to honour her keep clear obligation.

What you describe is pretty much exactly how the rules require the situation to play out.

As we have discussed, under Case 113, had C been closer in on B's hip, then it would have been different and C would have been obliged to respond, although she could have responded by hailing 'You tack', slowing down, and still been able to put B about again.

I suggest you consider the philosophy of rule 20 this way.

Rule 20 is a safety rule that requires a boat, in a tactically controlling position to windward of a close hauled boat approaching an obstruction that safety requires her to tack away from, to sacrifice (or at least diminish) her controlling position (lead) in a limited and controlled way, so that the leeward boat can safely avoid the obstructon.  Rule 20 allows the windward boat to minimise her detriment, and will penalise the leeward hailing boat if she abuses the rule.