Hiya, I guess a lot of it has to do with what you are trying to move ie the weight of your vessel? I have a 40ft steel
keeler weighing 15 tonnes loaded & run a Ford Lees marine
60hp tractor motor
through a Paragon hydraulic box. She's an oldie as is the boat (1965) but it pushes along at 9kts at 1100rpm (max) & 3ltrs an hour. A friend says put a Yanmar
in at half the weight but "hello", I would have to do probabaly 2100rpm to get anywhere near the speed of the Henry (Ford OK?)and how much fuel
would it burn? and what does a Yanmar
cost?? There are motors on Trademe that would probabaly suit your needs?? good luck.