... at what point is too close and the downwind boat is allowed to take action to avoid the collision and protest the upwind boat who has taken no action to avoid the collision.
.
.
.
Basically how close is too close and who gets to determine that distance
Let's call the windward boat "W" and the leeward boat "L". Rule 11 requires W to keep clear of L. Rule 16.1 requires L to give W room to keep clear if she changes course. Rule 14 requires both boats to avoid contact if reasonably possible.
If L changes course while the boats are still far apart - that is, while W is keeping clear, that is not "avoiding action" and W does not break a rule.
If L takes no avoiding action and there is contact, then W breaks rules 11 and 14. L breaks rule 14. If there is no damage nor injury, then L is not penalized, but she still breaks the rule.
Note that Rule 14 says that L "need not act to avoid contact until it is clear that the other boat is not keeping clear". L can wait until W is no longer capable of keeping clear before acting. If, at this point, it is no longer reasonably possible for L to avoid contact, she does not break rule 14 (see ISAF case 87).
In practice, L should wait until she needs to act to avoid contact, and then do so. To distinguish between the situations of acting too soon, and acting when necessary, it helps to present hard evidence to a protest committee. Wind speed, boat speed, and distance between boats are numbers that help protest committees make their decision. Since it is notoriously difficult to estimate distances correctly, it often helps to count seconds instead. If you can say "L was making 4 knots upwind; W was making 8 knots downwind, I altered course by 20 degrees and we passed 2 seconds later one half boatlength apart", then that's good information that a PC can use.
Regards,
Eric
