Prop for fuel economy (Johnson 115 V4)

[Captain Jeff]

Can anyone give some suggestions on propping for fuel economy? I have an 18" center console with a modified deep v hull and a 1999 Johnson 115HP V4. I have the stock prop on there. I don't care about hole shot but a prop that would allow me to run at lower rpms and save some gas when cruising would be great. Currently with the stock prop it does about 5,000 rpm at WOT and about 37 MPH. Thank you.

 

[steelespike]

Re: Prop for fuel economy (Johnson 115 V4)

The prop that produces the best overall performance/speed will produce the best economy.Without your present prop size We can't judge what size will perform the best. 37 at 5,000 rpm is the lowest wot rpm you would want.
Speed seems ok though you might get more.
Most would run the 115 at at least 5,500 max rpm.Rule of thumb an outboard will use about 10% of its rated hp in fuel at wide open throttle (wot).A 115 will use about 11.5 GPH (gallons per hour)whether pushing a house boat or a speed boat.Generally speaking try to get the best wot speed and you will get the best fuel economy, MPG.Start by being sure motor is well tuned and prop is in good shape and the bottom is clean.Then fine tune your setup.Raise the motor vertically to just before venting becomes a problem.Be sure it pumps water.Carry only what is necessary,distribute weight carefully.Adjust trim carefully as tou raise the motor.Speeds just above planing produce the most practical cruising speed.Could be at minimum planing speed or up to about 2,000 rpm higher.Experiment for the best.Something like smart tabs will allow to boat to plane at lower speeds and remain on plane easier.Once all is fine tuned a prop selection can be made for possibly even better performance.

 

[Silvertip]

Re: Prop for fuel economy (Johnson 115 V4)

There are lots of things you can do to get optimum fuel economy but increasing pitch to lower engine rpm is not one of them. By doing so you lug the engine which they don't like and my actually cost you in the form of worse fuel economy. Lower engine rpm has no benefit unless the engine revs higher than the manufacturers recommended wide open throttle rpm. All of the other things previously mentioned help economy. If you had a fuel flow monitor you could find the sweet spot for your engine. That's usually in the 2/3 throttle range. Get on plane quickly then throttle back a little. I use Smart Tabs and can attest to the fact that they allow staying on plane at slower speeds. Lighten the load and make sure you are not lugging around a boat full of water soaked foam. Don't run with live wells full of water if there are no fish in them. Go on a diet. Take along one six pack instead of two. Every little bit helps.

 

[Captain Jeff]

Re: Prop for fuel economy (Johnson 115 V4)

Thanks for the great advice. I took a look and I currently have a 14 1/2 X 19 prop on the 115. What do you think?

 

[steelespike]

Re: Prop for fuel economy (Johnson 115 V4)

I think you have it pretty close see if you can do the fine tuning to get a little more rpm then you'll have a pretty good setup.Then we can decide on a prop if necessary.

 

[walleyehed]

Re: Prop for fuel economy (Johnson 115 V4)

That's a 60 deg looper....5800-6000 will be best over-all.
5500 is lugging for that engine.