Heading for different gate marks

The situation

At the leeward gate two boats run down on the same tack — one committed to the left gate mark, the other to the right — and their paths cross between the marks.

The question

Does mark-room apply between two boats going to different gate marks?

The ruling

No. Rule 18 applies between boats at the same mark. Two boats heading for different gate marks aren't 'at the same mark', so there's no mark-room between them — they sort it out under the ordinary rules: port/starboard (rule 10) if on opposite tacks, or windward/leeward (rule 11) if overlapped on the same tack, plus rule 14. Pick your gate early and treat a boat bound for the other gate as a normal crossing.