If you have passed the mark, are home free

Buoy Room - Approaching and Leaving

RULE 

Part 2 - When Boats Meet

Section C - At Marks and Obstructions

Rule 18.1 When Rule 18 Applies

...it does not apply

(c) between a boat approaching a mark and one leaving it,

Buoy room rules do not apply at a starting mark surrounded by navigable water or at its anchor line from the time boats are approaching them to start until they have passed them... 

PURPOSE

Protect the rights of the leading boat.