Question 1
Yellow enters the zone clear ahead of Blue. Both boats tack and continue to round the mark. Blue becomes overlapped inside Yellow. Both boats Y-flag, what should the call be?

Answer 1
When Yellow enters the zone, rule 18.2(c) applies until Yellow passes head to wind. From the moment Blue becomes overlapped inside Yellow, rule 18.2(a) applies.
If the overlap is created by Blue bearing away, then rule 15 applies and Blue must initially give Yellow room to keep clear. If Yellow is unable to keep clear, penalize Blue.
However, if the overlap is created by Yellow bearing away, Blue acquires right of way, at least in part, through Yellow’s actions. Therefore the second part of rule 15 applies, so Blue does not have to give Yellow room to keep clear.
Because the overlap is established from clear astern, rule 17.1 applies.

Question 2
Yellow and Blue overlapped enter the zone. Both boats tack and continue to round the mark. Blue becomes overlapped inside Yellow. Yellow’s boom touches Blue’s hull. Both boats Y-flag, what should the call be?

Answer 2
The boats are overlapped when they enter the zone. Rule 18.2(a) and (b) apply.
Blue must give room and even if the overlap is broken (at position 4) she must continue to give room. After one of the boats passes head to wind rule 13 applies and rule 18 does not until the boats again are on the same tack. If Blue then chooses to go inside (position 5) she is NOT entitled to room and shall keep clear (18.2(b)). Penalize Blue.