# Need help with Prop on Gheenoe



## NativeBone (Aug 16, 2017)

A tiny tach is a good idea! Its, a great way to get some rpm data and just get a great feel for how the motor is running. With that said, what was the specs from the previous prop, meaning size, pitch?


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## John McFadyen (Jun 12, 2018)

NativeBone said:


> A tiny tach is a good idea! Its, a great way to get some rpm data and just get a great feel for how the motor is running. With that said, what was the specs from the previous prop, meaning size, pitch?


Yeah, a Tiny Tach is what I'm getting the rpm data from. No idea on stock prop... the motor had this one on when I bought it.


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## NativeBone (Aug 16, 2017)

hmmmmmm...if there no change in the setup, other than swapping the prop, I would somehow try to determine what the old prop size/pitch was and replace with same. Sounds like this may be the culprit.


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## John McFadyen (Jun 12, 2018)

NativeBone said:


> hmmmmmm...if there no change in the setup, other than swapping the prop, I would somehow try to determine what the old prop size/pitch was and replace with same. Sounds like this may be the culprit.


Based on some real quick research, looks like the Nissan/Tohatsu 8 hp four strokes come with an 8.9x7 3 blade. Can anybody out there confirm this? Would a difference in diameter of .4 inches make that much of a difference in rpm's?


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## flyclimber (May 22, 2016)

I will check what I have.

The short answer is yes a larger prop.

Longer Definition:
Larger prop will reduce slippage (Good thing) between the prop and the water. I repropped my Custom NMZ 15'4" with a 9.8 tohastu to a larger prop and picked up about 3-4 mph with two people in it.

The first step is data and more helps. I usually use http://www.mercuryracing.com/prop-slip-calculator/ is the site I used for my setup.

EDIT: 
https://www.microskiff.com/threads/gheeno-nmz-tohatsu-9-8.45736/ Here is my set up. If you need more help shoot me a PM.


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## John McFadyen (Jun 12, 2018)

freeclimber said:


> I will check what I have.
> 
> The short answer is yes a larger prop.
> 
> ...


Thanks for the info. I'm still trying to work this out. Discovered some fuel in the oil over the weekend, so I need to check to make sure the fuel pump diaphragm isn't letting fuel into the crank case.


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## HTXshallowwater (Jul 27, 2020)

John McFadyen said:


> Hey folks, this is my first post on the site, but have been a lurker for many years. I recently purchased a Gheenoe 15'4 (Highsider) that's powered by a Nissan 8 hp 4 stroke (NSF8a3). The stock prop had been replaced with a Solas 3 blade 8.5x7 aluminum prop. The motor runs great, I haven't had any issues... fires up on first or second pull, idles within range (900 rpm) and seems to run a like a champ. My only issue is that the rpm's are topping out at around 3000 at WOT. According to the specs, this motor should be running between 5 and 6000 at WOT. I do not have any speed numbers, as I haven't taken my GPS out yet. The motor is sitting on the transom w/ no jackplate, risers etc. Anybody have any ideas on why I'm not seeing higher rpms or any experience with these 4 strokes?


Did you ever find a good answer to this? I am in the same boat (pun completely intended). My rebuilt 15' 4" is running on a 15HP 1981 Johnson with a solas 4 blade 9.25X11 aluminum prop. I have a stingray jr and on the fly jackplate. Iv tried different weight distributions and gear arrangments but am only able to run between 10-13 mph at WOT. Tiny Tach reads 4300 at WOT. I know I need to get my RPMs up and I guess my fishing partners are typically on the larger side but I gotta get more than 13MPH. Any advice would be helpful.


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## GSSF (May 25, 2013)

HTXshallowwater said:


> Did you ever find a good answer to this? I am in the same boat (pun completely intended). My rebuilt 15' 4" is running on a 15HP 1981 Johnson with a solas 4 blade 9.25X11 aluminum prop. I have a stingray jr and on the fly jackplate. Iv tried different weight distributions and gear arrangments but am only able to run between 10-13 mph at WOT. Tiny Tach reads 4300 at WOT. I know I need to get my RPMs up and I guess my fishing partners are typically on the larger side but I gotta get more than 13MPH. Any advice would be helpful.


Almost all props for that motor will be a 9.25 diameter. only getting 4300 is no good- you're lugging. From my experience, you need an 8 or 9 pitch prop on that setup. That should get you upwards of 5k rpm. I would try a 3 blade if you can. Run the boat solo with a cooler up front first and see how she does. Then throw a buddy in and do the same.


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## flyclimber (May 22, 2016)

HTXshallowwater said:


> Did you ever find a good answer to this? I am in the same boat (pun completely intended). My rebuilt 15' 4" is running on a 15HP 1981 Johnson with a solas 4 blade 9.25X11 aluminum prop. I have a stingray jr and on the fly jackplate. Iv tried different weight distributions and gear arrangments but am only able to run between 10-13 mph at WOT. Tiny Tach reads 4300 at WOT. I know I need to get my RPMs up and I guess my fishing partners are typically on the larger side but I gotta get more than 13MPH. Any advice would be helpful.


I would try an 8 or 9inch pitch prop as big of a size that would fit. If you guys are on the bigger side maybe the 8. If you don’t hit a bunch of sand and hard bottom you could think about a stainless prop after you get running correctly With an aluminum one. They’re much cheaper.


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## HTXshallowwater (Jul 27, 2020)

GSSF said:


> Almost all props for that motor will be a 9.25 diameter. only getting 4300 is no good- you're lugging. From my experience, you need an 8 or 9 pitch prop on that setup. That should get you upwards of 5k rpm. I would try a 3 blade if you can. Run the boat solo with a cooler up front first and see how she does. Then throw a buddy in and do the same.


I picked up a box of old props from a buddy and switched them out until I found one that worked the best. Tach read 5800 at WOT. The prop that worked the best was a 9.5 X10. I think the top end of the 15HP ideal RPM range is 6500 if I'm not mistaken. May try your prop suggestion if I can borrow from a buddy. With the 9.5X10 I was able to consistently run 20mph so I almost doubled by speed from 10-13mph to 18-20mph. I think there is still room for improvement but I am beyond pleased with 20mph. 20 opens up a lot of the bay for me.


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## HTXshallowwater (Jul 27, 2020)

flyclimber said:


> I would try an 8 or 9inch pitch prop as big of a size that would fit. If you guys are on the bigger side maybe the 8. If you don’t hit a bunch of sand and hard bottom you could think about a stainless prop after you get running correctly With an aluminum one. They’re much cheaper.


I started at 12 mph using a 4 blade 9.25X11, 4800 @ WOT. I then switched to a 9.5X10 3 blade prop and ran 20mph, 5800 @ WOT. My motor is a 15HP 1981 2 stroke Johnson. When I hit 20 mph it did take a while for the rpms to build and for me to reach that top running speed of 20mph. I Hit 20 with a full cooler and buddy in the front. Based on this info what do you think should be the next prop I try? I have access to a bunch of different used props so I should be able to dial it in pretty good before ordering a fresh prop. If I can provide any more info that would inform your advice please let me know. This forum has been really really helpful so thanks to you and @GSSF.


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## flyclimber (May 22, 2016)

No problem. Post some pictures from side and rear of boat with the motor. Only thing left is to see the trim amount. Sounds like you got the right size and pitch.


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## HTXshallowwater (Jul 27, 2020)

flyclimber said:


> No problem. Post some pictures from side and rear of boat with the motor. Only thing left is to see the trim amount. Sounds like you got the right size and pitch.


Ill post some pictures when I get home but I tried several different tilt pin setting and the one closest to the hull (least trimmed out) seemed to be the best in terms of speed. If my motor is rated for a max RPM range of 5500-6500 and I am getting 5800 with this current setup do you think I should still try to reduce pitch or diameter to try and achieve higher rpms? I calculated my prop slip for this current setup using the mercury calculator at 16%. Thanks again for the help.


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## GSSF (May 25, 2013)

If a 10 pitch gave you those numbers and performance, stick with that or back down to a 9p and just watch your upper WOT RPMs. That way, if you throw an extra cooler or more gear in, you have the juice to push it. 20 mph on a 15'4" is solid performance for 2 people and a cooler/gear. Even with a 15hp. I'd be happy with that.

I can get 21 mph solo and empty with an 8hp 4 stroke on my 13 highsider, running an 8 pitch. I throw the wife and her bag of junk (extraneous stuff that chicks bring on a boat for no Effing reason) and only lose 2mph at WOT. As pointed out, these boats are weight sensitive. Add a heavy cooler and other items, the speed drops slightly.

I have a fixed TH marine Mini Jacker plate and the cav plate sits 1.5 inches above the transom. The setback is a bit over 4 inches. It took me awhile to find the sweet spot, but after playing with it a bit, I got her dialed in.

You're lucky to find a "box of props" you can try! But make sure the prop is in good shape, cause if you are trying a worn-out prop with less diameter or pitch variation due to wear (as happens with aluminum props), it will give you different performance than a new prop.


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## HTXshallowwater (Jul 27, 2020)

GSSF said:


> If a 10 pitch gave you those numbers and performance, stick with that or back down to a 9p and just watch your upper WOT RPMs. THat way, if you throw an extra cooler or more gear in, you have the juice to push it.
> 
> I can get 21 mph solo with an 8hp 4 stroke on my 13 highsider, running an 8 pitch. I throw the wife and her bag of junk (extraneous stuff that chicks bring on a boat for no Effing reason) and only lose 2mph at WOT.
> 
> ...


I have one of those on the fly jack plates so I can lower and raise it really easy. Very interesting to see the changes a quarter inch can make. The box of props came from my buddy who fixes old outboards in his spare time. I like your thinking with the 9p. I didn't have my biggest fishing buddy in the boat at the time so leaving a little bit of juice in the tank seems like a good route to take. Thanks again for the help.


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## HTXshallowwater (Jul 27, 2020)

flyclimber said:


> No problem. Post some pictures from side and rear of boat with the motor. Only thing left is to see the trim amount. Sounds like you got the right size and pitch.





flyclimber said:


> No problem. Post some pictures from side and rear of boat with the motor. Only thing left is to see the trim amount. Sounds like you got the right size and pitch.


Here are some pictures of the highest and lowest positions my jackplate is capable of. I have 3 different 9.5X10p props. I thought going to a prop shop would be expensive but after talking to a local prop guy for advice he said he would clean up & modify my props for $20 and was able to do it while I waited. He added some cupping to two of my props with the idea that it would allow me to run the motor higher on the jackplate without cavitating. So I have a "weedless style" prop unmodified (shown in picture) , A lightly cupped "weedless style", and a lightly cupped "modern style" prop that has the fatter blades at the base of each blade which should give me more surface area. His recommendation was to not go down in pitch but instead modify the props to allow me to run higher without cavitating to increase my rpms. What are yalls thoughts on this strategy?


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## flyclimber (May 22, 2016)

I would agree with your prop guy. I did that same thing with my current setup and haven’t looked back. It’s also time to send my prop for some touch up.
I would also try moving your trim pin back one to make your prop run more horizontally. 

here are some older pics of my Gheenoe when I had it. Yours may have a bunch more weight than I had in my NMZ


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## HTXshallowwater (Jul 27, 2020)

flyclimber said:


> I would agree with your prop guy. I did that same thing with my current setup and haven’t looked back. It’s also time to send my prop for some touch up.
> I would also try moving your trim pin back one to make your prop run more horizontally.
> 
> here are some older pics of my Gheenoe when I had it. Yours may have a bunch more weight than I had in my NMZ


Very cool. Looks like a fun rig. Yes mine is much heavier. Really went crazy with the fiberglass before I new the importance of weight. I built this boat before ever driving a boat so that was probably my first mistake. Despite being a little heavy it still gets way back in there. And now that I'm able to get her going a little faster I cant complain at all. Thank yall for the help. Cheers.


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