You didn't pay the tip on the service, that would be a service charge. You pay your tip based on the price of the charter. Do you go into a restaurant and ask the manager how much the power bill was for your little portion of the meal, or how much the lettuce was for your side salad, or how much the rent might be so you can divide it out by the number of meals plated per month? The fuel is a expense of the liveaboard, and, quite frankly, the cost isn't any of your business. If I fuel in Key West, I pay a premium over what I pay in Fort Lauderdale, but far less than I'd pay in Nassau. If you ride on my boat, I have 3 engines so your chances of getting home in a timely fashion are greatly enhanced. A boat like mine that has only 2 doesn't burn quite as much fuel. Will you penalize my crew because I have redundant systems for your comfort, enjoyment, and safety?