dumb hp ?

[Neptune]

Can someone enlighten me as to horsepower ratings? If engine A is rated 50hp at the crank and engine B is rated 50hp at the prop shaft, which engine is the more powerful pushing a boat?

 

[rwise]

Re: dumb hp ?

As I understand it, engine "B" as the gear case looses about 15% of the hp

 

[sloopy]

Re: dumb hp ?

it should be b most outboards are the same... the big difference is in I/O v drives

 

[Capt Ken]

Re: dumb hp ?

Once upon a time, engines in the good ole US of A rated their engines at the flywheel while engines from overseas rated theirs at the prop. This wasn't a problem until those ships started bringing a butt load of those engines into the states. Then folks started saying things like, hey bubba! why is it your non american engine is running rings around my trusty american engine. So some wise guy in Washington said, Hey Leroy, why don't we rate all engines the same way. Being we have no control over the non american stuff, we'll rate ours like theirs. Then the engine fairy waved his wand and poof appeared DieselWalt. Wasn't that about the time the Johnson 50 became a 48?

 

[Neptune]

Re: dumb hp ?

Sooo...in summary, power @ the propshaft is 10 - 15% less than what is produced at the crank due to friction loss in grearing, shafts, seal friction, etc?<br /><br />Thanks for the lesson. I had assumed that perhaps prop hp may be an amplification of the cranck hp due to gear ratios, etc.

 

[DJ]

Re: dumb hp ?

Neptune,<br /><br />Also be aware that outboards can be rated +/- 10% of stated horsepower. As an example: the 50 can be as high as 55 hp or as low as 45 and still be called a 50.

 

[Dhadley]

Re: dumb hp ?

And the OE's can play around with the rpm they rate the motor at. <br /><br />Dumb hp question? Nope!