I'm a sailor usually but we chartered a PC in the Pacific Northwest (San Juan Islands) a few years back because that area doesn't have the same perfect winds like the islands usually do. The company had a notebook with owner's comments - which I wish all charters had - lots of good tips. One of the things the owner included was fuel efficiency at different speeds - he should know better than anyone, he and his wife did the Great Circle Route with the boat. That boat would mosey along at 4-6 knots on very little fuel, there was a bad spot in the mid range and then you could get it up on a plane to move along quickly. Much more fuel efficient than the average "cabin cruiser/stink potter". Also great visibility from the flying bridge and great maneuverability in close quarters. I don't remember total fuel cost but it was pretty cheap I thought.

Life involves risks, take some prudent ones (NOT with the BVI ferries)!