Perhaps my frustration with charters that charge fuel surcharges is that they are rarely ever very forward about it.
I understand about the changing prices in fuel and pre-booking things, for sure, but, a couple things, first off. One is that if the change in fuel prices shouldn't be enough to change you from making a decent profit to a loss. If you are running that close to break even, perhaps you should charge more. Lets take a 200 gallon fuel usage, in which the price of fuel increased $1. If you are making less than $200 on a charter in which you are running a large enough boat or a long enough trip to justify 200 gallons of fuel usage, I would hope you are making more than $200...
Aside from that, perhaps, a base rate of what you expect fuel prices to be, then a disclaimer that if they go above xx amount, then there is a fuel surcharge... If I sign up today for a trip 4 months from now, many places I've seen have already tacked on a fuel surcharge, even though they have no idea what the price of fuel will be on the day I show up...
If it were me, in this day of fuel prices, I think I would assume a $4 per gallon fuel cost when estimating the cost of a trip. This would (should) give me some leeway in case of rising prices, and let my customers know I am going to absorb some of a fuel surcharge, but that anything over $4 per gallon, I would have to charge, based on fuel consumption, and how many people are on the boat. I don't think there is any ethical way I could (and I've seen others that do this) charge a set rate per person for the trip, knowing that I would be profiting from the surcharge... I would make some sort of rule that 2 - 3 weeks prior to the trip that I would be finalizing the pricing for any surcharges, if any, that apply, and that there would be an opt out if the surcharge was more than a certain amount per person, perhaps around $20 or $25, depending on the overall cost of the trip (day trip, I'm assuming here).
James, I appreciate your view, but, if the trip isn't costing a lot, meaning a very small amount, it may be in your best interest to go ahead and run the trip... A little good publicity and public relations is a very good thing, and may end up being very profitable in the future...