RPM Question for You 15 hp Owners

David Palmer

David Palmer

Active member
Early this summer I bought a used '74 Evinrude 15 hp outboard motor. I recently put a tach meter on it, and it maxed out at around 6050 RPMs. I did a little research on the internet and found out that according to a 1978 Johnson sales brochure, full power operating RPM for the 15 hp motor is rated at 5500 -7000 RPM.

Should I look into getting a new prop that would increase the RPMs to the 7000 range or am I good at where I stand now? I know little to nothing about props and good RPM speeds, so any advice would be most appreciated.

Grace and peace!

David

 
How does the boat perform with the prop you are running now?? I would only go down in prop size if the boat is sluggish getting up on plain, otherwise it sounds like your right there in a good range!

Dan
 
in that case an inch of pitch less will most likley be a good move. I believe the formula is 200 rpms per inch if i remember correct.

I'm about to do the same on my southbay, with just me in the boat my 15 is a bit slow on plain, but then boogies just fine once up, but in nasty conditions especially in a head sea it takes a long time to get on top.

goodluck, let me know how you make out!


Dan
 
David, You need to try the prop with diferent loads and under different water conditions. I would probably stay where you are unless like has been said you need more power for getting up on plane especially with a load. By staying in the middle of the RPM range you should be OK. Lugging an engine is just as hard on them as over revving so go for the best performance while staying in the RPM range.
 
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