Please, Prop Help Johnson 115 / 16' Boat

Hello Fellow Boaters:

I have a prop question: We bought a virtually new 2005 Stratos 170FS (16' Fish/Ski, basically a bass boat), with a 2005 Johnson 115 HP 2-stroke J115PLSOR, and the existing prop is a 14"x17P 176215 Johnson OEM.

The boat is fast enough for me, gets to 45mph quickly with 80% (~475 lb.) loading which is normal for us, and the engine reaches max revs of 5500rpm at WOT also very quickly.

I do not need the boat to go any faster. We use it mainly for putting around and pulling skiers / tubes / kneeboards and such.

I would like a spare prop and was thinking a 4-blade would be a good choice.

However, the only OMC 13-spline 4-blade props I can find are 12.5" x 19 Solas.

Wouldn't this prop allow the engine to reach max WOT revs even quicker? I'm thinking instead I'd want to load the engine a bit more without creating more speed if that's possible, which means at least a 14 x 19 4-blade, and preferable larger diameter. Not more pitch 'cause I don't want more speed.

So my question: Is my thinking correct, and if so, does anyone know where I might look for a larger diameter 19P prop for this engine? Solas makes them, but they all seem to be 15 spline for larger engines.

Sorry for such a long first post, and thanks.

Re: Please, Prop Help Johnson 115 / 16' Boat

Ok You need to forget about the maximum speed.The motor needs to be able to rev freely within its rated rpm I believe 4500 to 5500.
If it turns out to be faster than you like just throttle back to a speed you prefer.
Forcing the motor to a lower rpm with prop selection wastes fuel and stunts power for extra loads or water sports.
Diameter is a secondary consideration when selecting a prop.You may note that generally as pitch goes up diameter goes down.
Usually as you add a blade diameter goes down partly to maintain rpm with the added drag from the additional blade.
Further it is usually suggested to reduce pitch 1" when going to a 4 blade to maintain rpm.
Generally a 4 blade will improve low to mid range performance while losing a little top end.
Sometimes it can result in about the same speed.
Pitch is the key number involving rpm and power or speed.
Judging from your description your propped just about perfectly for all your activities. Your prop size is very reasonable as well.
A 4 blade 16" pitch prop would be a good choice for a spare. You could use it for water sports when heavily loaded.
You will probably find that 16" pitch has fewer choices and will cost more.
it should keep your rpm close to what it is,ideal,.

Re: Please, Prop Help Johnson 115 / 16' Boat

Thank you very much for you help.

One correction, the existing prop is 14"x19P 3-blade, not 14x17. I'm satisfied, and do not need any extra top speed. Almost always run throttled back to 30-35 mph which is way plenty for me.

Solas offers a 12.5" x 19P 4-blade which looks like a good choice.

What difference(s) can I expect with this prop? I'm guessing not much by way of hole shot or top end because of reduce diameter but increased blade count, and perhaps slightly smoother putting around?

Thanks again

Re: Please, Prop Help Johnson 115 / 16' Boat

As I mentioned usually it is suggested to go down one inch in pitch when going to a 4 blade to maintain rpm.
You should notice an improvement in hole shot and ability to stay on plane at reduced throttle.
Also may handle better around the dock.Top end will usually be reduced.