Two boats meet on opposite tacks at the start line — who keeps clear?
The port-tack boat. Before the starting signal there is no special starting right-of-way rule in play — Rule 21.1 only bites once a boat is returning to the pre-start side after her starting signal. Until then plain Rule 10 governs: port keeps clear of starboard, on the line exactly as anywhere else on the course.
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<p><a href="https://sailing.kiwi.nz/v/iO2AflEGihU/">Source: Sailing Kiwi</a></p>