Hi, Ken:

Glad you're finding the site helpful. And thanks for your letter: I love a good rules puzzle!! I will answer - attempt to answer??? - your questions in red below. I think your interpretations are mostly right on, by the way. Best regards,

Uncle Al (W3854)

PS: I sail Wayfarers mostly in Ontario (Canada) and Michigan (U.S.)  Where do you sail?? I'd like - with your OK - to post this as Case 66 of my Quiz, so would like to be able to say where you sail. I'm guessing England?
 
 

... In our races there are 3 cruiser classes and because of the confines of the estuary and tides we all start together but sail different courses. Occasionally, the fleets converge around a mark and I guess that if it is to be left on the same side by boats from different classes then Rule 18 applies to all boats when about to round. 

The situation that happened recently was where 3 boats were approaching the same mark. Two class 1 boats on broad reaches, one port and us on starboard, had to round the mark leaving it to starboard and the third - a class 3 boat - was sailing in the opposite direction, close-hauled on St'bd and had to leave the same mark to port. The distances and speeds were such that all three boats would arrive at the zone at effectively the same time. Sorry that I don't have a diagram for you.

The way you describe this situation, I picture it like this:

Question 1:  Does Rule 18 apply if all boats are not passing on the same side or should Rules 10 & 11 mainly apply between all three boats?

18.1 When Rule 18 Applies
Rule 18 applies between boats when they are required to leave a mark on the same side and at least one of them is in the zone. However, it does not apply
(a) between boats on opposite tacks on a beat to windward,
(b) between boats on opposite tacks when the proper course at the mark for one but not both of them is to tack,
(c) between a boat approaching a mark and one leaving it, or
(d) if the mark is a continuing obstruction, in which case rule 19 applies.

Given the fact that rule 18.1 states "Rule 18 applies between boats when they are required to leave a mark on the same side", Rule 18 can apply only between boats required to round "buoys to port" or between boats required to round "buoys to starboard" but not a mixture of the two. Any other interpretation of the rules text would result in chaos because the rule could not be applied - e.g. try to resolve an overlap situation between Grey and Black above!
In the situation above, Rule 18 does not apply to Black (starboard close-hauled). Thus, Rules application goes back to basics, Rules 10 and 11 as you suggest. Therefore, both Grey and White will have to keep clear of Black: Grey as windward boat (Rule 11) and White as port boat (Rule 10). The one limitation on Black will be Rule 16 which states: "When a right-of-way boat changes course, she shall give the other boat room to keep clear."

2:  Does the inside class 1 boat on port have right to room to round inside us on st'bd & force us to change course?
Yes. Rule 18 does apply between Grey and White, and White will be entitled to mark-room from Grey
Of course, Black will be a complicating factor since she has right of way over both White and Grey and will rank as an obstruction, and the new Rule 19 may well come into play if both Grey and White choose to pass Black on the same side. Since both Grey and White would likely pass astern of Black, White would again be inside boat and be entitled to room to pass astern of Black as well. White and Grey could also try to cross Black's bow although that would be rather suicidal and counter-productive in the situation above. The choice of whether to go in front of or behind Black would be Grey's since Grey is the right-of-way boat over White. (see Rule 19.2(a):
"A right-of-way boat may choose to pass an obstruction on either side."

3:  Does the inner class 1 boat on port have to keep clear of both the other boats?
No!! See above.

Hope this helps. Best wishes for good sailing, Uncle Al (Wayfarer 3854  SHADES)