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Old 19 June 2013, 09:26   #1
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HP definition

Is outboard power determined at crank or using prop thrust. I'm aware car and motorbike bhp changed from wheel to crank but is that the case for outboards?Essentially is my Neolithic Mariner 30hp stroker putting out the same power as a spanking new 30hp Honda four stroke. Obviously taking age into account
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Old 19 June 2013, 10:02   #2
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AFAIK, it used to be Crank, but is now Prop, +/_ 10%

Older engines tend to give reduced HP, I guess as compression decreases over time???

Inboards are Crank, I think...
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Old 19 June 2013, 10:24   #3
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Willk, so transmission losses are 10%?An old 30hp will be at crank and new ones are at prop. Meaning that the new 30 is more powerful than the old 30.
As for compression losses there is no smoke and if anything the unit will have loosened itself over time. But I was ignoring the ageing of the engine just wondering about what you answered in your first sentence.
The 30 hp deux temps Mariner is a peach of an engine.... Yamaha of course. And weighs nothing.
:-)
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Old 19 June 2013, 10:40   #4
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Hi

new outboards are rated at the prop and older engines were rated at the power head but sorry I dont know when this change was made.

like all engines they will also lose HP over time. I know it is slightly different but there are a few top gear episodes where they have taken sports cars that are 20+ years old and retested the HP and found it to be a lot lower i.e. more than 25%
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Old 19 June 2013, 10:50   #5
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Cool, and there is also the bit where twenty year old two stroke bikes are more powerful than new ones as they've loosened up.
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Old 19 June 2013, 13:42   #6
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The standard changed in 1983. There may have been a few years after the new standard was published where nobody had a clue!

Quote:
Willk, so transmission losses are 10%?An old 30hp will be at crank and new ones are at prop.
I think he means the power has to be within 10% of spec. so a new 30HP leaving the factory today will be 27-33HP.
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Old 19 June 2013, 14:12   #7
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Originally Posted by Poly View Post
I think he means the power has to be within 10% of spec. so a new 30HP leaving the factory today will be 27-33HP.
Yes !
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Old 19 June 2013, 15:45   #8
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My engine can't be pre '83 !!!!! And still work. So as a 30hp it is rated the same way as new ones basically. At the prop.
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Old 19 June 2013, 15:58   #9
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It's normall to lose some compression as years of use passes by. Applying power tunner as directed on can every 100 worked hours can make wonders revitalizing old 2 stroker engines. That's if you don't usually use aditives mixed along with fuel.

Happy Boating
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