How do they rate horsepower on outbourds.

[Ruffis]

I have a 1975 Johnson 115 that we just bought. Someone told me that because it is a 1975 it was rated at the flywheel and it is actually an 85 horsepower motor... Is this correct..

 

[b.gagnon]

Re: How do they rate horsepower on outbourds.

I think there is about a 15% difference so I would say your motor puts out about 98hp

 

[wilde1j]

Re: How do they rate horsepower on outbourds.

Ruffis, the difference is newer motors are rated as output power at the prop shaft, older motors are rated at the crankshaft, which ignores losses from the gearcase.

 

[Brew]

Re: How do they rate horsepower on outbourds.

Any idea what year OMC made the switch to measuring HP at the prop?<br /><br />Cheers.

 

[wilde1j]

Re: How do they rate horsepower on outbourds.

Not sure of the exact time, but my '85 140 is prop shaft rated.

 

[mellocj]

Re: How do they rate horsepower on outbourds.

A local boat guy told me my '63 Evinrude 75hp was rated at the flywheel, and that the '75 Johnson 115hp I got was rated at the prop

 

[G DANE]

Re: How do they rate horsepower on outbourds.

Hi Ruffis and Mellocj<br /><br />As far as i know OMC started propshaftrating around 1981.

 

[Bob_VT]

Re: How do they rate horsepower on outbourds.

Everyone is right. Yes you have a true 115 hp but it is at the powerhead. The new motors are rated at the shaft. Mercury has been rating at the prop shaft much longer and others just took time to catch up.<br /><br />Bob