How to calculate percentage of total horsepower?

[zentodd]

I’m new to this idea but I’ve recently viewed a post - I think by Smitty - saying to keep your engines below 60% (maybe it was 70%) total horsepower for maximum longevity of your engines. I originally thought that meant 60 or 70% of maximum rpms, however I don’t think that is correct. Would someone - please explain how to calculate percentage of horsepower? Thank you in advance.

[MonteVista]

Here is some info from the web.

Mathematically, horsepower equals torque multiplied by rpm. H = T x rpm/5252, where H is horsepower, T is pound-feet, rpm is how fast the engine is spinning, and 5252 is a constant that makes the units jibe.

So, all you have to do is find your engine manufacturer's torque vs rpm chart and use the above formula.

Good luck!

[Jim_Gandee]

Zentodd, not exactly sure what engine you have but according to this chart for the W04C-T1 th HP curve is clearly visible. 60% of the available 210HP is 126HP which equates to about 2200 rpm.

https://www.marinepartssupply.com/me...vicemanual.pdf

[zentodd]

You guys are awesome! Thank you both!

[purduepilot]

Except you have no idea what torque is being produced when you're running at a given rpm on your boat. The torque vs. rpm chart just tells you the maximum torque the engine can produce at that rpm. So you can likely run at a higher rpm and still be under that magic 60% power number. Or depending on your boat, if you're running at 2200 rpm and plowing a huge wake, the engine fuel governor may be dumping the maximum fuel load into the engine to put out the max torque as it struggles to maintain that rpm and it could actually be a worse operating point than going faster and getting on plane at a higher rpm but lower torque.

[Jim_Gandee]

Purdue, I agree with your assessment. However, pending any other published data specific to the vessel in question I think the Hino performance curve is about as close as one could get.