I think this is an interesting one because the situation was complicated and applicable rules changes so fast, so we'll publish our take on this. I've chosen to identify the boats only by the last two digits of the sail number, so if you want to know who was who you'll need to do a bit of cross checking.
70 was approaching the windward mark on starboard tack in shifty winds, about one boats width to windward of the layline as the wind was swirling about unpredictably. Other boats were following on starboard tack.
34 was approaching on port tack, a boats length or so below the layline, ahead, but probably not clear ahead of 70.
83 was behind, most likely clear behind 34, also on port tack, but may have been fractionally overlapped to windward.
34 tacked under 70's bow without a hail to 83, and rounded the mark without 70 having to luff above close hauled. As 34 tacked 83 had to bear away under 34's stern to avoid a collision. 83 then tacked, but made contact with 70 as the tack was being completed. 70 did not alter course.
34 took a 720 alternative penalty.
Rules that apply
Initially 70 was right of way boat (rule 10) and 34 and 83 were required to keep clear. At this stage rule 18 did not apply because the boats were on opposite tacks and 70 did not need to tack round the mark (18.1a, 18.1b).
34 had right of way over 83, either because she was leeward boat (11), or else because she was clear ahead (12).
70 was an obstruction to 34 and 34 could, but did not hail 83 for room to tack under rule 20.1. 34 was entitled to decide which side to pass the obstruction (19.2.a) but if she had chosen to pass to leeward may have been required to give 83 room to pass to leeward as well (19.2.b). Following ROW boats on starboard probably constituted further separate obstructions.
34 then tacked, and after passing head to wind lost right of way over 83 and so was required to keep clear of 83 (rule 13) and was still required to keep clear of 70 (rule 13 takes over from rule 10). 34 completed her tack within the zone and inside 70 without 70 having to alter course above close hauled, so did not break rule 18.3. 83 had to bear away behind 34 as she tacked, so 34 broke rule 13.
After bearing away behind 34 83 tacked, still required to keep clear of 70 (rule 13 takes over from rule 10), and made contact with 70 at the end of the tack. 70 didn't change direction either to windward or leeward. 83 broke rule 13. 70 did not attempt to avoid contact with 83 so probably broke rule 14. However it is not clear that there was sufficient time for 70 to avoid contact, nor was there any damage or injury, so 70 is exonerated under rules 14.a and 14.b.. 83 would have been able to complete her tack without making contact with 70 if 34 had not broken rule 13, so is exonerated. 34 took an alternative penalty and did not gain a significant advantage in the race as a result of her rules breach (44.1.b) so is exonerated.
No further penalties are therefore appropriate.
(these don't form part of the protest documentation)
34 and 83 were adopting a high risk approach to the mark, and it was not likely to end well.
Its very difficult to remember exactly what happened in a complicated situation like this where the applicable rules are rapidly changing. Its always likely that sailor's recollections will vary. The protest committee's lot is not a happy one, and they just have to make the best evaluation they can of what is most likely to have happened. Fortunately in this incident the different recollections, some of which are noted, did not seem to us (the PC) to make a significant difference to what rules applied. In other circumstances it would probably have required a lot of time to sort out exactly what went on.
70 would have been entitled to bear away onto the rhumb line before the incident started and force 34 and 83 to tack away or take her stern. They were lucky that 70 was taking a conservative approach to the mark in the swirling wind.
If 34 had hailed for the obstruction that 70 presented then 83 would have had no alternative but to keep clear, either by tacking short of the lay line or by taking 34s stern. 83 was extremely lucky that 34 did not hail.
Although in theory 34 could have born away behind 70, in practice further starboard boats probably made this impossible, especially as if she was overlapped with 83 she would have been required to give 83 room to pass astern too.
It took 7 people about 30 minutes to work out what happened on the water, and about another 45 minutes for me to write up exactly what rules applied when. On the water you have about 10 seconds to work it all out. Its not surprising we all have problems applying the rules from time to time, and its always best to avoid complicated situations if you can.