I just did a weekend with Ocean Divers. Their boats seem to hold about 30 divers packed, we had just 5, 5, 6, 6, 7, 10, 10, and 12, plenty of room, good crew.
some photos http://www.images.dewbrook.com/KeyLargo2007/
a 3 minute movie http://www.youtube.com/watch?v=wQLxA3Rd8dc