You can even take it one step further.

Collect more than enough up front to cover the cost of the shared boat. The balance remaining from the deposit for the shared cost will be provided in cash as part of the checkout.

The other option is for a host to pay the cost of the boat in total and treat the boat like a family vacation house with any other visitors as "guests". Many great "guests" will cover the tabs ashore and other entertainment based on their ability to pay.

We would never sign for a boat we could not easily fund 100% ourselves. You just never know when you will have to cover all the costs from your accounts.