Big C

My wife and I chartered a boat and also paid to enter the derby. i was lucky enough to catch the biggest king for the day and am still on the board, but not top 5. I paid for the charter and, since no mate, I tipped the captain 15%. I want to be completely fair and give the captain what is appropriate but since I've incurred all the expenses, what is fair? Most examples are different than my situation, it seems to me anyway, and if I deduct the charter cost and taxes there likely wont be much left to divide. Thoughts????