What year did the propeller horse power ratings come into effect?

[ShoestringMariner]

Hey folks, just wondering what year Johnson and Evinrude started rating their horsepower at the prop instead of the crankshaft? I’ve heard that it’s a difference of about 15hp in the 70 hp range. I.e.; early 70 hp models = 55 at prop vs 70 at prop for newer.

Or or is there any truth to this?


Thanks

 

[racerone]

Mid 1980's is when it changed.-----It takes an amazing amount of power to run a water pump.-----Takes an amazing amount of power to churn oil in a gearcase.

 

[ShoestringMariner]

Thanks. I’m looking at a 1984 model... trying to determine if I should look at later 80s and 90s instead

 

[boobie]

Later 80s and 90s...…..

 

[jimmbo]

85 was the first yr OMC used propshaft ratings. A 70 didn't become a 55, a 65 or 60 perhaps, but not a 55

 

[ShoestringMariner]

Thanks guys. I understand there’s some parasitic loss, but 15 hp seems very high to me. I would have assumed maybe a couple HP difference at most, but I’m no expert obviously

 

[Joe Reeves]

This subject pops up from time to time... and it puzzles me.

Back in 1962 when the electric shift first came out, the 40hp model was advertised strongly, and I remember the dealership having a small advertisement movie from OMC that I watched quite a few times. Memory has it that, at that time, one of OMC's top advertisement points was that the horsepower was rated at the propeller as compared with their top competitor (Mercury) whose horsepower was rated at the powerhead.

I'm aware that OMC could later change whatever they decided to change whenever they decided... and may have... or apparently did. However.... does any other member recall that advertising film of 1962?

 

[racerone]

No , they said that the brake HP was " certified " by OBC or was it BIA ?--------Prop rating was not mentioned I believe.

 

[jimmbo]

The OBC in time became the BIA, which later became the NMMA

Mercury said their motors were rated using an SAE protocol.