headhunter:
We could use our buying power to get better deals once we know we can count on more people. I know Captain Ray on the Sundiver will start to offer discounts when you get a group of 8 or more people, so that might be a great way to start. This way, we don't need to fill a whole boat. Eventually, we could work out way up to filling a whole boat.
Sounds like fun. Some random responses --
-- You probably don't need to fill the whole boat to make it work financially if you do the charter. When a shop charters a boat, the break-even point on the charter fee is some fraction of the maximum diver load -- the exact amount will depend on the boat, how much the shop is charging divers, etc. After the shop reach the break-even point, every space they sell beyond that goes toward their profit.
-- Also, if you do decide to charter the whole boat, you can probably sell spaces to non-scubaboarders. Once last year I chartered the Sundiver and had people calling me wanting to get on the boat.
-- On the other hand, lining up boats on weekends during prime diving season (summer to early fall) will pose some challenges -- most weekend dates are taken by shops. I booked with Ray six months in advance when I set up that one trip (on a summer weekend) last year. Also, if you want to negotiate a volume discount for a group but don't have enough to charter the whole boat, it may be tougher to do with a shop than with one of the boats on their open-boat dates (which will be less frequent on weekends this time of year).
-- Committing to a monthly dive from the get-go might be ambitious -- you could try it as a one-shot event, and see how it goes, what the turnout's like, etc. I'd be interested in trying to go, for example, but doing a boat trip for me always involves nine-dimensional chess of what's going on with the household schedule, buddy availability, etc, etc.