luv2golf, Katkandu is a luxury 42' catamaran (Capt. Rick) does daysails. You can do the snorkel, lunch at Caye Caulker; or snorkel and have a great lunch on board. You can pm me for particulars or visit the website: www.belizecharters.com
Minimum 6 people, but these are mostly private charters, so your party would have the boat to themselves which means you get to set the schedule as to how long you want to snorkel.