Recommendations for splitting expenses on charter

[Lake-Effect]

On our one (1) BVI charter 2 years ago - 3 couples - we split the charter and provisioning costs equally, and those of us who drank worked out those purchases amongst ourselves. Mooring, fuel and other common expenses - we kept notes and receipts and split later, and each couple paid individually for dining out, entertainment, etc. It all worked out... but it helped that we're all good friends. Still, KEEP RECORDS. People forget, especially when there's too much fun happening.

I've also helped manage an annual sailing get-together which draws in 7 to 11 boats from Canada and the US. We often arrange marina deals, prepaid dinners, and have some small awards. The financials are a bit messier, and it's even more important to set expectations, explain in advance how costs are going to be shared, and KEEP RECORDS. I had an online registration system for signing up, printed out spreadsheets for tracking who's paid, and kept a steno pad aboard listing all transactions.

[boatpoker]

Went to dinner a couple of times with another couple who had a penchant for $250 bottles of red wine. When the bill came he would say "just split it down the middle". We don't drink red wine and we don't go out to dinner with them anymore either.

I'd be quite happily shamed/shunned by them.

[KenKo]

We start out by using a formula that everyone is asked to work through individually. It goes like this: cost of food squared + cost of alcohol squared x 8 + cost of misc. boat/mooring/etc. squared x 4, then taking the square root of the whole amount. What makes it work, is that after all that calculating, everyone is happy to simply use a common kitty and share the costs equally.
Have fun and enjoy the cruise....