Remember? That's not how it works at CCV. "Air Hogs" surface when they will, then they can wait in the Sunshine on the boat until everyone with gills surfaces at the suggested max 1:00 BT on dives #1 & #3. Anybody that's been coached, especially by LDS trip leaders, should have no problem getting 1:00 in the shallows of Roatan's South side. Your group might even decide to extend the maximum BT to 1:20 or whatever for these two daily dives. On dives #2 and #4 we regularly do 1:45 BT dives, some 2:00.
Make sure everyone attends the free Buoyancy Clinic and get your LDS DMs and Instructors in teaching mode. If not, get them to the CCV dive shop for a full course. Buoyancy and air consumption are basic building blocks that "air hogs" simply have not yet acquired.
Although you can put all 18 on one CCV boat, no idea why you would do that. Split them by ability, maybe 12 and 6. I have seen dive groups continuously insist on 18+ on the same boat. By day 2 a lot of people bail for the ease of the shore dive. You're soon down to 7 or 12 divers.
On day #1 or when doing Mary's Place or Calvin's, likely everyone that is assigned will be on-board. On day #1, you're not going to want to be there with all of your rubber suited friends flopping around like fish...trying to figure out what they're doing. By day two or so, you can share a boat with 18, but there will still be some fish-a-floppin.
If you want to divide them up or if you decide on 18 aboard...Check with CCV in advance and arrange that. If you plan in advance you can hire another DM, and this is a pure guess, but I'm thinking maybe for $7 a day x 18 persons (a guess) you'll have hired a second DM.
I'd split the group. I know that socially that's a tough one, but these are decisions and special arrangements that should be made while engaged in the booking process itself.
