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sledderdoc

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Hello everyone .... I had a qu

Hello everyone .... I had a question regarding horsepower. I am upgrading my old 81 14hp evinrude to a 20hp 4stroke yammy. Now that hp is measured at the prop how would this compare to the old style. ie. is this the same as 25hp at the motor?
 
"Engines (in general)

"Engines (in general) are normally rated as Break HorsePower (BHP) to get shaft horsepower you multiply the BHP X .7

So if your old EV was 14 BHP the Shaft HorsePower would be 9.8

You could work that backwards too, the 20 (SHP) divided by .7 would be about 28.6 BHP under the old way of doing things..

Of course that is measured/adjusted to a uniform set of conditions in order to conform to the ISO standard.

So unless the tempurature is 77 degrees, with 30% humidity and air pressure of 29.61 and you are at Maximum Wide Open Throttle, your motor is "not" developing that horsepower.

Just a numbers game - needless to say, jumping from an older 14 horse, to a modern 4 stroke 20, you will notice a difference, particularly at the top end - from the start I would suspect that they are close though, since the 2 stroke "kicks" alot better than a 4...."
 
"Thank you very much Graham, t

"Thank you very much Graham, that does help.
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"Hey Graham, You are saying th

"Hey Graham, You are saying that a prop shaft rated model is 30% more powerful than a powerhead rated model?

I do not think that is accurate. The necessary change in direction of the power output (caused by the gearcase)from vertical driveshaft to horizontal propshaft, is what derates the power. It should be more on the order of 4-5%"
 
Chris - just took the definiti

Chris - just took the definition and numbers right from the ISO standard definition.

Shaft horsepower is Break horsepower X .7

With the older model motors I don't know for sure what they rated - that was kinda up to the mfg - but if it was BHP then the numbers should be good - at least according to the ISO....
 
"Chris - you did get me intere

"Chris - you did get me interested though, and did a bit more reading. I would suspect that prior to using the SHP rating for outboard motors, the builders probably used "net horsepower" to rate them as opposed to BHP.

And although it never had a "standard" definition it is said to be 10 to 20% less than BHP which is measured at the flywheel.

It went on to state in the early 70's when Britain first adopted the new rating to try and "standardize" the way automotive engines were rated, that a 450 BHP engine became a 375 (net) by definition overnight.

So it seems like you can take BHP and pick a factor out of the air to reduce it by and call it "horsepower"....

However, there is a standard definition for BHP (derived by ISO) and SHP (which is a factor of BHP) as I noted in my initial post..."
 
Just wanted to say the differe

Just wanted to say the difference between my old 88 15hp evinrude and this new 4stroke yamaha F20 was hugh!! Finally able to bring my little 12ft inflatable to plane with 4 people in it and actually pulled a tube! Definitley impressed. Also a miser on fuel compared to the old one. Thanks again for all the input it helped make my decision to purchase it.
 
Oh ya once I'm all broke i

Oh ya once I'm all broke in I will post a GPS top speed as long as I have the nerve to hold it open. 400cc of motor pushing 166lb boat goes!

Cheers Norm
 
"Oh ya one more thing. I now a

"Oh ya one more thing. I now am selling my motor but can't seem to nail down the year. Its offically an evinrude super 14 (commercial), model# HE14RSF.
The best I could tell its between 88-91. Anywhere else on the motor a guy can look to see for sure?"
 
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