Originally Posted by Polwart
But to include a fuel consumption per distance numer in the spec for an engine would be dependent on the boat and propellor, wheras fuel consumption at any given rpm/throttle position is not.
So e.g. if an engine burns 30 LPH at WOT and on a particular rib tops out at 30 knots it will be using 1L per NM. The same engine on a "better designed" (faster) hull, or with a better prop might give 40 knots at WOT - so using just 0.75L per NM. But put it on a semi-displacement craft and it might not get above 20 knots - and will burn 1.5 L per NM. All the same engine - all using the "optimum" prop for the situation - but very different results and nothing to do with the engine design...
But, I already "have" a boat and a propellor. I want to know how far it will go for a specific amount of fuel.
You see my point. "IF a particular rib tops out at..........".
I need to know this before I start my calculation.
Agreed there are a huge number of variations, boat speed, revs, sea state, weather, no. of pax etc. but to say 10 gals per hour, or whatever, gives one NO chance of establishing performance.
But I suppose we are looking at/for diferent things. I want to know the specific performance of that engine on a specific boat. You want to know about the performance of an engine (in isolation).