We're overtaking a slower boat to leeward — when does right of way flip?
Four rules take turns. While you're clear astern, Rule 12 makes you keep clear of the slow boat — and she counts as an obstruction. Passing to leeward, Rule 19.2(b) makes the outside boat give the inside boat room. The instant the inside boat overlaps the slow boat, Rule 12 dies and Rule 11 takes over — the overtaking boats now have right of way. Then Rule 15 gives the slow boat a moment to keep clear. You don't have to hail for room, but it's smart to. World Sailing Case 41.
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<p><a href="https://sailing.kiwi.nz/run/case-41-overlap-flips-right-of-way/">Source: Sailing Kiwi</a></p>