Max RPM

[compcrasher86]

The Max WOT RPM on my '87 140hp evinrude v4 is supposed to be 5500. Right now my engines WOT is 6000rpm. I am thinking of adjusting the throttle arm so it hits the dash at 5200rpm so I dont go over WOT. Anybody have any other opinions?

[Miguel]

change prop?

[Capt. Bob]

change prop?

 

[compcrasher86]

sounds like a plan. Any suggestions fora prop for my engine with a '73 22-2?

[GoneFission]

What are you running now?  There should be some numbers stamped in the prop hub - check them out and we can decode for you.

[compcrasher86]

Its pitch black out where I am but I went out with my flashlight and my point and shoot. Pics are available but I found two sets of numbers stamped on the prop.

The first is next to one of the blades on the exterior and reads 13-3/4X15. The other number is on the inside edge right next to the bolt and reads 4012. I beleive the outer one is the right set...

The prop was given to me by the previous owner and he had no clue what it went to. It required me to buy a special propelleor spacer washer from the local marine store because it wasnt fititng on right.
____________________________________________________________
While rumaging for a flashlight I found a nice shiny black prop in the workshop. The engraving is very shallow but it appears to say "Vortex Mi-Wheel" It also says "1992" on the other side, then something and then what appears to be "13-2'5X17" Right next to the splines there is a clear engraving with the code 991211 and the word Michigan. I took a nice macro picture of the  "13-2'5X17" so here it is if anybody can decipher it

(This is the spare prop i found!)


I can take more pics, just ask.

[Capt. Bob]

The first number is the prop's diameter. That's measured across the blades. Think of it as the size hole the prop "drills" in the water.
In your case 13-3/4".

The second number is the pitch. That's how far the prop moves through the water in one (1) revolution.
In your case 15". (it doesn't really move that far due to slip but that's another post altogether).

OK, it's late and I'm under the weather but here goes. :(

For every 1/4" change in diameter, you change WOT by 200 rpm.
Reduce the diameter and you increase rpm.
Increase diameter and you decrease rpm. (duh)

Pitch change is 200 rpm for every 1"
Increase pitch will lower rpm.
Decrease pitch will increase rpm. (duh again).

Now it's not as easy as it sounds but since your looking for a decrease in WOT of 500 rpm, the thing that jumps right out is to increase the pitch to 17".

That stated, many of us have spent time and money playing with "propage" (is that a word?).

Getting the exact combination of pitch and diameter for your setup (boat, motor and load) not to mention type of use, takes some experimenting. Throw in motor height and blade number and you'll be drinking early.

Hope this helps get you started in the cash outflow necessary to become a prop "expert".

Good luck and keep us posted.

[compcrasher86]

seeing as the season here in marblehead is winding to an end, maybe this is best left as a winter project. I plan on going around to the regular places (Evinrude dealer in town, propeller store a couple towns over, and some boating friends) and try and get an oppinion on what is my best bet. Maybe over the winter I can figure out more about this stuff and by spring I bet I'll be ready to buy a nice new prop.

I am still open to comments and suggestions for a prop (perhaps somebody with a similar 22-2 setup)

[Mad Dog]

That's a great explaination. I think we should call you Prof. Bob from now on.

MD  

[Capt. Bob]

That's a great explaination. I think we should call you Prof. Bob from now on.

MD  

It was my 200th post.
I wanted it to be special
Plus I didn't even touch on cupped and un-cupped and material.
All that stuff is for GF.
He's the "dog" on props. 8)

[compcrasher86]

hmmm so that means my spare prop is a 17" pitched prop. Maybe I should try her on for size...

Once I patch the hull I will put her in for the day and test out the spare prop...

[Capt. Bob]

hmmm so that means my spare prop is a 17" pitched prop. Maybe I should try her on for size...

Once I patch the hull I will put her in for the day and test out the spare prop...

Sure, why not.
You already own one but be careful.
It would appear that your spare is not only 2" bigger in pitch (decrease rpm) but also 1/4" SMALLER in diameter.

Do the math.
2" pitch increase= 400rpm reduction
1/4" diameter decrease = 200rpm increase
Net loss = 200rpm ...on paper.
As I stated earlier, you don't really know until you spin 'er up and go for a ride. Might have been the PO used the prop you now have on the boat for say...skiing.

It won't hurt a thing to try and it starts to give you a baseline to work from on prop selection for your boat. (yes, I have several in my garage).

Lastly, I believe there is a prop on the market that has changeable blades which would allow you to experiment with pitch and diameter. I have not idea on costs though.

Good luck.
 

[Miguel]

Not a good winter project, unless you are in the tropics like me.  You need to be able to take the boat out for a trial ride and judge the change in performance with each propeller.