HP Ratings

[DMontana]

I am not trying to start any kind of arguments here about exceeding HP ratings.
Now that that has been said, I am just curious as to what they base these ratings on.
For example, I have a 1988 pontoon that is rated for a max of 70hp. Is this based solely on torque of the motor, weight or both?
I am considering putting something a little more current on my boat.

 

[belairbrian]

Re: HP Ratings

the formula for HP ratings is more complicated than motor torque. it is based on length, transom height, where the steering is, engine weight, hull design and i think fuel tank location. The formulas are available from the coast guard website.

While I've never done a pontoon i went through it on my Grumman CC. it was built in 81 and at the time rated at 40hp. But when I followed the instructions in the coast guard home builders manual It would be 60 hp. There may also be engineering factors (and even liability concerns) the manufacturer considered.

Keep in mind as well that 4 strokes tend to be heavier than 2 strokes.

lastly most sttaes can cite you for a HP rating higher than the decal rating. Not saying it happens that often but the laws exist.

 

[DMontana]

Re: HP Ratings

Thanks,
The 4 stroke vs. 2 stroke weight concern is why I was asking.
I'd rather not put something on there that is going to lower the rear end too much. And I do not want to start relocating fuel tanks and batteries to disperse the weight.

 

[belairbrian]

Re: HP Ratings

here is a link to the iboats engine specs

Outboard Engine Manufacturers

some examples
1988 mercury 70 weighs 265
2005 mercury optimax 75 weighs 360 lbs
the current mercury 75 hp 4 stroke weighs 399lbs (per mercury website)

 

[DMontana]

Re: HP Ratings

Thank You,
Very helpful info!