Re: Mercury outboard fuel consumption
Actually, the old HP/10 formula was thought up in the days when 2-stroke outboards were rated at the crankshaft.
So, if you use this on a later-model outboard rated at the prop, the value you come up with is gonna be a bit on the low side.
But, HP/10 is sure a lot easier to figure out in your head than HP/8.21 or whatever correction factor you jack into the equation!!!
Here's a good example of this:
Old Merc 1150 rated at crankshaft, approx 11.5 GPH WOT;
Old Merc 1400 rated at crankshaft, approx 14 GPH WOT;
Later-model Merc 115 (which was for all intents and purposes a 140 rated at the prop as 115HP), approx 14 GPH WOT.
And so on, and so on.
Still lots easier for my Pea-Brain to divide HP by 10 and then just jack in a bit more GPH to come up with a S.W.A.G.!!!
And of course the original formula works great on all the Antique Fossil (er I mean "Classic") Mercs we're still playing with!
BTW it shouldn't matter what type of hull you're pushing, if the motor is truly running at WOT, in its rated operating rpm, it's gonna consume the max amount of fuel.
Of course, the type of hull you're pushing will greatly change the Speed and MPG values, as will cruising at the most efficient speed for the hull/motor configuration; but we're not talking about those, only specific consumption at WOT.
Cheers........ed