115 Evinrude RPM?

[pokman]

Hi guys I have a 17ft Four winns with a 115 evinrude, both are 1996. Issue I am having is I am running a 19p SS michigan wheel prop, but I can only get it to spin to 5100-5200 RPM running at 42mph (gps). If I drop down to a 17p I can get it up to 5500 rpm where it is supposed to run but I can only get 37mph out of it. Shouldn't this motor be able to spin to it's max rpm without a problem. These speeds are on decent water with only myself and a 1/4 tank of gas. Anything ideas to get my rpms up will be appreciated, the motor is set in the right position as far as the bolt holes.

 

[steelespike]

Re: 115 Evinrude RPM?

Is the 17 the same brand and model prop and the same material?
In my limited research it appears that thje 19 might be slightly too much prop
The dry weight of your boat I believe is 1760;not a flyweight.
Is the motor in excellent tune,throttle opening all the way?
Is the motor as high as possible on the transom?Antivent plate (just above the prop) should be even with the bottom to about an inch above.

 

[pokman]

Re: 115 Evinrude RPM?

The 17p is a aluminum and dinged up so I know that isn't a good prop, I just thought this motor would have no problem reaching it's max rpm with the 19p prop. I am gonna take it out and see where the anti cavitation plate is when were at wot and see if the motor needs to be raised.

 

[50 feet]

Re: 115 Evinrude RPM?

The 17p is a aluminum and dinged up so I know that isn't a good prop, I just thought this motor would have no problem reaching it's max rpm with the 19p prop. I am gonna take it out and see where the anti cavitation plate is when were at wot and see if the motor needs to be raised.

An aluminum prop on a heavy Four Winns boat just doesn't seem right in the first place! I would get a stainless steel four blade 21 pitch for that boat! I'm willing to bet that prop you have is flexing like crazy not too mention the dings in it! I would try that

 

[pokman]

Re: 115 Evinrude RPM?

The 17p aluminum was just going to be my backup because I thought the 19p ss would run at 5500 rpm- that is what is suprising me. I was thinking about a four blade but isn't it true that at same pitch if you go from 3 to 4 you will lose rpms which I don't want to do? I was thinking about trying a 18 or 19 four blade.

 

[steelespike]

Re: 115 Evinrude RPM?

There are plenty of heavy boats running fine on al props.
No doubt the ss would likely produce good numbers but whether worth about 3 times the cost??
Our only real numbers are with a 19" ss prop
We will be likely changing brands and material both introduce variables that really can't be acounted for. And we may add a 4 blade.
I think a 17" al prop will do better than your dinged up 17.Probably not 42
but respectable.If you go to a 4 blade a 16 may deliver similar results,better hole shot stay on p-lane with less throttle, better control on plane and at the dock. But a little less top end.
Same brand and model ss prop should have better hole shot, easier control just on plane close to the 42 top end.

 

[pokman]

Re: 115 Evinrude RPM?

Tried a omc ss 17p today and was happy, ran 40.3 at 5500 rpm. I think a 18p ss would be perfect probably give me 1 or 2 mph but I am gonna stick with the 17p.

 

[riptide09]

Re: 115 Evinrude RPM?

I have an 03 17' Four winns with an 04 115HP Johnson. I am running an OMC aluminum prop. 13.25 x 17. I don't know if this is the original size prop however I have good reason to believe it is.

With only myself in the boat, full tank, I can get 5400 RPM @ 45.5 MPH if the water and wind conditions are pristine.

If I load the boat up with say 5 adults and gear the best I can do for RPM is 5200. My top end speed varies between 41 and 43 under most circumstances.

I considered swapping the prop out a lot of times when I first got the boat. I did all kinds of research and caluclations but just was never quite sure what I wanted to do. The more reasearch I did and the more I drove the boat, including towing tubes and skiers, the more I figured I had the best prop for the mix of boating I do.

 

[Dhadley]

Re: 115 Evinrude RPM?

Sounds like you're trying to gain rpm by simply changing props. If we were doing it we'd try to gain rpm with the set up. The set up for a 3 blade 17" aluminum prop, even in new condition, will not likely be the same for a new 3 blade 17" ss prop.

Gaining rpm by a pitch change alone will in most cases result in lower top speeds. Gaining rpm with set up almost always improves top speed, mid range and holeshot. Switching to a lower pitch in cases like these is always a last resort.

 

[pokman]

Re: 115 Evinrude RPM?

The 17p I just tried is a ss, and I am happy with it 40mph at 5500. I just found a 18p ss omc raker prop I am going to try I think this might hit the sweet spot I am looking for.

 

[Dhadley]

Re: 115 Evinrude RPM?

Again, keep in mind the Raker, which is a very good prop as long as it's never been reworked, will run best at a higher X dimension than a standard ss prop.