How many HP is a 10HP outboard?

[Inselaffe]

My 1999 Yamaha 9.9 HP 4 stroke is said to produce only max 8HP at prop (Clymer Manual).

I understand that there are shaft etc losses between engine and prop, but when an engine is quoted by the manufs as X HP is this at prop or engine?

I think I can vaguely remember someone saying that they changed the rating at some specific year from at engine to at prop?

Thanks

Leigh


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[mirabriani]

Right I'm answering this one,

On the basis of a 3 1/2 Tohatsu being substantially the same engine as
several others which are termed 3.3 hp
I deduce that if you multiply the difference (.2 hp) by 3
the result will be .6 hp
Therefore I deduce a 9.9 is really a 10.5hp

I read somewhere that the reason for lots of 9.9's outboards
was for some silly tax reason in some silly country

See! Briani

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[mikewilkes]

my Yamaha man in Inverness said with a little tweeking he could make it a 15 hp. Doesnt anwser your question, just throws another thought into the equation!!!

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[studgies]

can I tweak my 5hp Evenrude??

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[Joe_Cole]

Some engines are restricted versions of bigger brothers in the same range. There's usually a restriction in the carb intake (which is easy to remove). Other than some different settings on the carb and ignition these engines are identical. I suppose its cheaper to manufacture them this way.

Your dealer may well have been right about the Yamaha engine.

Joe

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[sailorman]

France

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[greatspirit]

Whether the Yamaha 9.9hp 4-stroke is really an 8hp or 10.5hp it is still an excellent engine especially with the high thrust propeller...very popular with cat owners.

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[Birdseye]

There are all sorts of different national standards as to whether the power is measured at the crank and without alternator etc Same with cars and bikes. And certainly, in bikes, the Jap figures bear no relationship to what is developed at the rear wheel.

So what you say doesnt surprise me one bit.

<hr width=100% size=1>this post is a personal opinion, and you should not base your actions on it.

 

[ex-Gladys]

As of approx 1990 all Jap motorcycle HP measurement was back wheel, not crank

<hr width=100% size=1>Larry Botheras

Anderson 26 "Amber"

 

[Inselaffe]

Thanks,

Someone on the Mobo forum said he thought they changed from at crank to at prop in early 80's (82/83), but it sounds like the ratings should be taken with a small pinch of salt.

I will stick with my 9.9 (8HP) after it saved me from my own stupididty on the weekend, but it made me wonder about the validity of the 'which size outboard for which size boat' question if the HP you think you are getting isn't what you have anyway, especially if the difference varies from manufacturer to manufacturer.


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[Inselaffe]

How do I tell if its a high thrust prop?
I checked for a number, but its illegible.

Thanks

Leigh

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[bruce]

over here, USA, many small lakes have a 10 hp max limit on motors, so makers down tune larger motors and sell them as 10 hp to get around rule.

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[supermalc]

I was told that in 1989 the rating was changed from the crankshaft to the propshaft.

This is why a 15hp pre 1989, and a 9.9hp post 1989 are the same.

The 9.9 Mariner I bought was the same engine as the 15hp...just had the electronic rev limiter set lower.

As I've discovered, a small hp engine will move a boat almost as fast as up to 15hp. To go faster takes a much larger engine.

<hr width=100% size=1>Malcolm.
<A target="_blank" HREF=http://geocities.com/malcsworld/>http://geocities.com/malcsworld/</A>
Take a look at my boating pages.

 

[Joe_Cole]

The shape of the blades. Someone (I think on this forum) described the high thrust blades as looking like Mickey Mouse's ears!

Joe

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