Taking more than your room

The situation

Rounding the leeward mark with mark-room, the inside boat swings wide on the exit and forces the outside boat — who had kept clear — up and out of her water.

The question

Mark-room protected the inside boat going in. Did it cover the wide exit too?

The ruling

Mark-room is only the room she needs to sail to the mark and make a seamanlike rounding — not a licence to swing wide and push the outside boat around. Rounding out, the inside boat is the leeward, right-of-way boat — but as a right-of-way boat changing course she must still give the outside (windward) boat room to keep clear (rule 16.1). If she swings wider than her room and forces the boat that had kept clear to give extra room, she breaks rule 16.1, and because she took more than her mark-room rule 43 no longer exonerates her. A tidy 'in wide, out tight' rounding keeps her inside her room.