Outboard HP Rated at Motor or Prop?

[marlinqld]

I have always wondered if I was being fed a load of BS over the years. I was told in the past that older outboards were rated at the motor. IE: 75 HP was at the power head, and was told they lost 10% down the shaft and through the gear box, giving the 75HP a rating of say 68HP at the prop. :-?

Then ive been told new outboards are rated at the prop. IE; 75HP this years model is actually 75 HP at the prop. :-?

Is this fact or fiction? Truth or BS? Do different manufacturers rate theirs at the motor and some at the prop? Do older models lose 10% of their power down the shaft to the prop? :-/

Would be interested to hear from you experienced guys on this subject. All greek to me,


Mike

[PADDLES]

can't help you with the older models mike, but from what i've seen of specs for most of the new outboards they actually state that the measurement is at the prop. i'm guessing that if it's not stated then you'd have to assume the figure is at the crank like most motor vehicle specs :)

[Noelm]

yep, that is the case, though not too sure of exact HP "losses" but there is a few bits and pieces that can take power, like the water pump and so on, so an "at the prop" is much more a true HP rating, I think it came about sometime in the late 80's maybe, the Japanese I think used this rating system for their outboards first.

[TOPAZ]

I bought a Swiftcraft Sea Hawk MkII in 1984 - it was a 1979 build hull fitted with a 1978 115HP Evinrude V4 2 stroke - 115HP at the flywheel.
I replaced this in 1996 with a new Evinrude 90HP VRO r stroke, which was rated at the prop. The two engines were virtually identical in performance, i.e. 115HP at the flywheel equalled 90HP at the prop.
ALL engines have a degree of power loss between flywheel and propellor, as does you car between engine and wheels.