Port meets starboard on the beat
The situation
Both boats are beating to windward and their courses cross. Green has the wind on its starboard side; Red has it on the port side.
The question
Who must give way, and what are Red's options?
The ruling
Green (starboard tack) has right of way; Red (port tack) must keep clear under rule 10. Red can bear away and duck behind Green's stern, or tack onto starboard. But a tack earns nothing instantly: while tacking, rule 13 keeps Red as the give-way boat until she's on a close-hauled course, and rule 15 then requires her to give Green room to keep clear.
Port keeps clear of starboard. Duck the stern or tack early — a tack doesn't instantly hand you the rights.
Opens the situation on the boat-length grid — scrub it and see exactly how the boats meet. Free, no account needed.
Rules cited
See the underlying rule: Rule 10 — On Opposite Tacks.