You cannot tack into buoy room

RULE 

Part 2 - When Boats Meet

Section C - At Marks and Obstructions

Rule 18.3 If two boats were approaching a mark on opposite tacks and one of the changes tack,  and as result is subject to rule 13 in the zone when the other is fetching the mark, rule 18.2 does not thereafter apply.  The boat that changed tack

(a) shall not cause the other boat to sail above close-hauled to avoid her or prevent the other boat from passing the mark on the required side, ...

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

Protecting the lead boats rights