Mike
My Warrior 195 is about the same weight as the 640 @ 1040kg without anything on it. My Optimax is a 150hp and has no trouble (as you would expect) pushing us along a a rapid rate of knots 36 in fact. She consumes an average of 1 litre of fuel per mile, which is on a par with 4st engines. On trips out to the rips which are roughly 26miles each way plus all the up and down movements connected with drift fishing, we would typically cover 80+ miles in a day and consumed about 80 litres of fuel. Smaller boats ie 165 with 60hp 4st engines used around 70 litres for the same trip, considering the weight difference I don't think thats to bad. At tickover 4st engines are definitely quieter than my engine but when cruising I don