Preamble of section C states that rule 18 does not apply at a starting mark surrounded by navigable water. Therefore, Red (the windward boat) is not entitled to room, and must keep clear in accordance with rule 11 (boats on the same tack, overlapped). Red is forcing Blue to change her course to avoid a collision. Therefore Red has not kept clear, has infringed rule 11 and will be disqualified in a protest.