I am getting conflicting reports on horsepower ratings for outboard motors. How is this figured now versus years ago? I have been told that years ago the hp rating was takin from the engine whereas now it is at the prop. So does that mean an older 40 hp could really only be rated at say 30hp vs a new motor truly being 40 at the prop? I ask this because I want to downsize motr I have for size reasons and dont want to lose too much hp.
I’m hoping someone has the explanation of this because it doesn’t make sense to me. Horse power is simply The amount of work done per unit of time. If you say that there are differing power measurements from the power head to the prop, That would imply that there is an inefficiency from the motor crank to the prop. I can’t think of anything that would reduce the motors final output other than the impeller, and friction in the gears, So where does this 10 hp go then. Dynamically it doesn’t make sense to me. What next they’re going to start taking power measurements from the tire and not the engine? Oh man…… I just explained it to myself,………I get it. It makes perfect sense. See what happens when you talk to yourself. Its just a play on the efficiency. Thats really dumb. The hp should always be measured from the motor. I really shouldn’t post my confusing thought process but oh well
It’s actually a better way for you to know what power you’ll see in the real world. Let’s say two manufacturer’s have a 150 hp motor at the powerhead but one motor has an extremely inefficient driveline, the difference at the prop can be significant. I remember the old force 125’s that were so popular (cheap) they only made around 99 hp at the propshaft…at the time OMC was already rating at the propshaft so a 115 OMC was really a more powerful motor.
Jason.
I wonder if someone in the know can help on this one. I had “heard” that Mercs used to be rated at the powerhead and OMC at the prop shaft. This may be a wives tale, but it would be nice to know.
I would also like to hear more on this. The physics of this does not make sense as Matt stated. If anyone out there has more knowledge about this, It would be an interesting read for me and something I would love to learn more about.
Bassman
It is power loss through friction/heat…gears meshing take power to turn, the power needed to rotate these relatively heavy, touching parts…is used up before it can turn the propshaft/prop. It is much more prominent in a car. My old fox body mustang made 225 hp at the crankshaft…but after it went through the gearbox and driveshaft/axle it only made 189 hp on a chassis dyno…more power would be lost if it was an automatic tranny with more junk to turn…to put it simply.
Jason.
Sounds right, but I can’t figure out why my 1954 10HP Merc is faster then the new ones. And no, it is not a Hurricane, just an old 10 HP Mercury.
Jetcat hit it. Some designs are more efficient. Some are built for endurance, some for speed, some just cheap!
Another thing to keep in mind. The motor companies must build their motors within 10% of their stated HP. Some are hi, some are low. The new e-tecs and Rude motors consistently put out more HP than what the sticker on the motor says. The Rude 225’s have close to 240HP right out of the box!
-J.
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