Load up 20-40 tourists on the catamaran (based on the size), and charge them something like $40-50 each.

Costs (other than the boat itself and local fees/taxes) would be a crew of 2 or 3, food and booze, and whatever cut the local resorts get for referrals.

Biggest challenge would likely be to make sure the tourists don't get too drunk and fall overboard. (seen it happen once, the captain wasn't pleased).