Changing prop for 40 HP 1992 Evinrude

[4DaughterMan]

I am changing props on my 16 ft aluminum boat, tiller steering, 40 HP Evinrude, 1992. I have been running a 11-1/2 inch diameter, 19 inch pitch prop for about 14 years now. It was on the boat when I boat it. I have mostly used the boat for fishing and 3 trips per year to Lake Powell. Now I have changed my use, Duck hunting. I painted it camo and it looks great. Anyway, needless to say, with 2 hunting buddies, a few dozen decoys, shot, and snacks, I am way heavier. I know I need a different prop now. Top end is not that important, I just want to be able to maneuver while heavy and potentially choppy water. So, I wouldn't be able to find the same prop if I tried, but in my search I am finding a lot of 12-1/2" diameter in either 13,15, or 17 inch pitch. My question is how much difference am I going to see increasing my diameter but decreasing my pitch. What are your thoughts? I know I need to do all the tests with the tach but just looking for thoughts. Right now, I can get up on plane with full tilt and then while I am going, cut throttle, slightly adjust tilt and then throttle up again. My top end is around 29 MPH. I can live with the lowest top end without revving out.

 

[steelespike]

Re: Changing prop for 40 HP 1992 Evinrude

As you decrease pitch diameter will usually increase. What ever pitch you decide on if its say a 17" it should act like a 17".
Diameter may vary slightly with various brands.If you start getting into more exotic props diameter may be a little more unpredictable and extreme.
If you want good control,strong hole shot,resisting ventilation(cavitation)and smooth operation a 4 blade may be a good choice.
The Solace props have a good reputation.
I have a 18 ft bare Crestliner with a 50 tiller running a OMC 19" prop It is used for all sorts of stuff, loads of people,huge loads of construction materials even getting a 180 lb slalom skier up on one ski. We were lucky to have a 100lb adult spotter.

 

[4DaughterMan]

Re: Changing prop for 40 HP 1992 Evinrude

Have you ever tried a lower pitch prop on your Crestliner? If so, which pitch and how much difference did it make?

As you decrease pitch diameter will usually increase. What ever pitch you decide on if its say a 17" it should act like a 17".
Diameter may vary slightly with various brands.If you start getting into more exotic props diameter may be a little more unpredictable and extreme.
If you want good control,strong hole shot,resisting ventilation(cavitation)and smooth operation a 4 blade may be a good choice.
The Solace props have a good reputation.
I have a 18 ft bare Crestliner with a 50 tiller running a OMC 19" prop It is used for all sorts of stuff, loads of people,huge loads of construction materials even getting a 180 lb slalom skier up on one ski. We were lucky to have a 100lb adult spotter.

 

[steelespike]

Re: Changing prop for 40 HP 1992 Evinrude

Never had the need for less pitch.I think the large footprint of the 375 lb bare 18 footer helped it get up on the water easier.
In fact it had an old 25 Gale originally and would plane easily with 6 adults aboard.Guessing about 20 mph.
I believe your 40 has the same gear ratio as the 50. It appears that your 16 is good full sized boat so planing should be fairly easy.
Once you have your performance specs it will be easier to tell what or if you need a prop change.
Unfortunately I don't have any rpm or speed for mine and it has been passed down to my son now.
If your motor can make 5500 rpm lightly loaded using the 19" prop and a 2.42 gear ratio with 12% slip speed could be about 35/36 mph.