That is why I got the 55 horse, 4-stroke Bearcat. Much better on fuel then that 105 2-stroke Chrysler at the same trolling speed. Like I said, I have no scientific calculations with that 105 HP. I know this. It was our camp-boat when we camped for two weeks on a boat-access only island-campsite in the NY Adirondacks. It was a three mile run from "mainland" to the island. So, a 6 mile trip. I carried three 6 gallon tanks with me most of the time. One round trip of 6 miles at a slow place used 1/3 of a tank (2 gallons). Once – with the whole family in the boat – I ran it full throttle, to the island and back and just made it on 6 gallons. That is 1 gallon per mile as I figure it. Note the engine no longer had the OEM CD ignition. I converted it to standard battery-coil from a Chevy car after the CD units burnt out twice. It ran no different and fuel usage was the same either way. Makes me wonder why that CD box and weird spark plugs were ever there to start with.
I also hated to leave that boat behind. Just one of those things. I had many old engines, tractors, cars, trucks etc. to either sell, junk, or dump. I offered that boat with the good 105 HP on Craigslist first for $400. Then for $250. Then when we had only three days left – I offered it for free. Still no takers. I junked/dumped four old boats and two RVs when I moved.