Preamble of section C
states that Rule 18
does not apply at a starting mark, but Rule 11 (boats on the same
tack, overlapped) requires the windward boat (Red) to keep clear of the leeward
boat (Blue). Blue is allowed to luff up to head to wind, but no further. Blue's
luffing is only restricted by rule 16, i.e. she must change
course moderately enough that Red can keep clear.