US Sailing Race Management Handbook.

I don't have my copy with me here, but I believe it recommends gates be set 5-8 boatlengths apart. As others have already mentioned, gates too close play havoc with rule 18. For catamarans, I would set gates on the wide side. Due to their speed approaching the leeward mark, "about to round or pass" can extend well beyond 2 boatlengths.

Regards,
Eric