As one who makes his own diesel (FAME), I can well understand boatyards wanting to control what fuel goes into their boats. I know my stuff and am happy to use it in my car, my sisters car and my boat, but I know of people who's fuel is of a poorer quality. They don't mind as it goes into heating systems or engines that can cope with it. but it wouldn't be right to shove it into a hire boats tank to get top dollar back as a refund. Personally if I was running a fleet, I'd have locked fillers on the boats fuel tanks, with reciprocal agreements with some other yards where necessary. It's about more than just making a bob or two extra on the fuel sales.