Operating Cost Comparison

I am trying to compare the operating cost of two very different boats (displacement is about 4 to 1, one uses jet drives and the other uses surface props, ...). Normally, if maximum speed is the same operating cost is considered to be proportional to displacement, but I think that regardless of speed operating cost per hour of operation would be a function of applied horsepower. If both boats cruise at 80% of rated power, the operating cost per hour would be proportional to rated power. What do you think? Is there a flaw in my logic?

Cheers;
Mike Schooley

 

Are you talking overall operating costs, or simply fuel consumption?

 

I'm really interested in overall operating cost, which for these boats if going to be mainly fuel. One boat weight 8.5 tonnes and does >55 knots on 2 850 HP engines. The other is 90 tonnes and does 45 knots with 2 3,700 HP engines.

I guess the maintenance cost of 2 3,700 HP engines will be higher than 2 850 HP engines, but less than 4.35 (i.e. 3700/850) times as high.

Cheers;
Mike Schooley