A question about measuring horsepower.

[Old Ironmaker]

I read somewhere on the forum where horsepower was rated at both the prop as well as the flywheel. Can someone please explain the difference to me. Our boats here in Canada have a metal tag from Transport Canada where it says what the maximum horsepower is rated for the vessel as well as maximum weight and number of passengers. I wonder if it's prop horsepower or horsepower at the flywheel?

I hope this is the proper forum for this question. Mods please move if required.

 

[Scott Danforth]

Pre early 80's motors were rated at flywheel hp, post early 80's at prop hp. the capacity tag on you boat and the LEO's dont care how its rated. the rating is the rating. the HP tag on the motor must be equal to or less than the rating tag on the boat.

 

[jbcurt00]

Yep ^^^

IIRC, 1982 was about the year the change was made.

 

[GA_Boater]

I read somewhere on the forum where horsepower was rated at both the prop as well as the flywheel. Can someone please explain the difference to me. Our boats here in Canada have a metal tag from Transport Canada where it says what the maximum horsepower is rated for the vessel as well as maximum weight and number of passengers. I wonder if it's prop horsepower or horsepower at the flywheel?

I hope this is the proper forum for this question. Mods please move if required.

It doesn't matter if the HP is prop or flywheel. The marking on the motor determines the legal HP. No Water Cop is going to ask what method was used to determine the HP rating.* Besides, the prop rating method was not applied to all motors at the same time. For example Merc lagged the others before switching to prop rated HP.


* Something bad has to happen before thinking about asking the question and that will be long after the operator takes a sobriety test.

 

[jimmbo]

For example Merc lagged the others before switching to prop rated HP.

Merc was the first among the North American manufactures. Merc started proprating the V6s and Inline 6s in 1982, the 66cu" in 1984. OMC didn't stsrt until 1̶0̶8̶5̶ 1985

 

[jimmbo]

. Our boats here in Canada have a metal tag from Transport Canada where it says what the maximum horsepower is rated for the vessel as well as maximum weight and number of passengers. I wonder if it's prop horsepower or horsepower at the flywheel?

I hope this is the proper forum for this question. Mods please move if required.

Up here in Canada, at least in Alberta, there has never been any concern about exceeding the max recommended HP. In fact most Outboard boats were sold with bigger motors. I bought a boat, a 15 footer rated for 90hp, dealer was more than happy to bolt a 140 on. One of other boats I had was rated at 150hp, I saw a couple of the same model with 175hp and one with a 225hp on it. I recall in 1986, a guy wanted to put a Merc 225 on a Vanguard Banshee, a flip of a Glastron GT150, which was rated for 90hp. A dealer put it on.

 

[GA_Boater]

Merc was the first among the North American manufactures. Merc started proprating the V6s and Inline 6s in 1982, the 66cu" in 1984. OMC didn't stsrt until 1̶0̶8̶5̶ 1985

Told ya Merc was later. LOL

Whatev - It wasn't an across board thing like the HIN requirement in 1972 which is my point. Prop HP or flywheel HP rating means nothing when it comes to overpowering. 115 is 115 is 115, etc.

 

[jimmbo]

You got me GA Good catch!:embarassed:

 

[GA_Boater]

You got me GA Good catch!:embarassed:

I fixed it, Jimmbo. I stand corrected on the chicken/egg bit. I thought Merc was later than OMC. I know Merc was often accused of underrating their outboards, especially the higher HP's. :noidea:

 

[Old Ironmaker]

Up here in Canada, at least in Alberta, there has never been any concern about exceeding the max recommended HP. In fact most Outboard boats were sold with bigger motors. I bought a boat, a 15 footer rated for 90hp, dealer was more than happy to bolt a 140 on. One of other boats I had was rated at 150hp, I saw a couple of the same model with 175hp and one with a 225hp on it. I recall in 1986, a guy wanted to put a Merc 225 on a Vanguard Banshee, a flip of a Glastron GT150, which was rated for 90hp. A dealer put it on.

jimmbo, a dealer would have zero problem selling anything a customer wants to buy, in the event of a failure or accident an insurance provider will definitely have an issue paying out a claim for a boat with a over rated power plant. I have recently learned that Canadian authorities go by the Transport Canada plate for rated maximum HP and are strict about it. Some will change the rated HP tag on the engine to make it appear the boat owner complies.

 

[robert graham]

Just wondering about how much HP would be lost through the lower unit gearbox and lubricant?....maybe 5% or so????

 

[Old Ironmaker]

Told ya Merc was later. LOL

Whatev - It wasn't an across board thing like the HIN requirement in 1972 which is my point. Prop HP or flywheel HP rating means nothing when it comes to overpowering. 115 is 115 is 115, etc.

So if the HP is measured at each location they will match? I wasn't really asking about over powering, that just came up. Why the switch from flywheel to prop measurement. There must be a reason and if anyone knows someone here will. My guess the industry came to an agreement to standardize ratings so as to not cause confusion amongst buyers.

 

[Baylinerchuck]

I think a 115 hp at the prop motor is stronger than a 115 hp at the flywheel motor since some power is lost through the drive train.

 

[roscoe]

Yes it was a standardization deal.
yes, about 5%.

But, the NMMA manufacturing standard allows for a 10% difference from labeled HP to allow for manufacturing variances..
So a 90 hp could could be 99 hp, or be 81 hp, and still be sold as a 90. :facepalm:

And a 115 could actually be as low as 103.5 hp. Making a strong 90, almost as strong as a weak 115.

The same goes for cars, not every motor rolling off the assembly line is gonna produce the stated "400" hp.

 

[jimmbo]

I think a 115 hp at the prop motor is stronger than a 115 hp at the flywheel motor since some power is lost through the drive train.

My Prop rated 1984 115 merc was stronger and faster than my crank rated 1982 140 evinrude on the same hull.