# Propeller selection



## DearJon (Mar 30, 2013)

Ok fellas,

This one has been debated for a long, long while, but I'm going to open another thread on it. I am not getting exactly the performance I want from my boat/motor with my current prop. Maybe someone on here can give me a few pointers. I had a 1994 Honda 35 hp four stroke on the back of my G3 1548. When it finally gave up the ghost, I repowered with a 2012 Yamaha F40. When I installed the new motor, it did not come with a prop. Much to my amazement, the old prop off the Honda fit perfectly. It was an old aluminum Michigan Wheel 10.75" dia X 13" P that was pretty worn and had lots of dings in it. I suspect it might have measured 11" in diameter when it was new. I went out and did all the break in with this prop. After break in, my top speed was 32 mph at about 5800 RPMs. Sounds pretty good, right? Well, I thought that if I bought a new prop, it might do even better. So, I purchased a Solas aluminum 11" dia X 14" P prop. I figured if the old beat up 13 pitch prop was spinning at 5800, I could stand to lose 200 RPMs by going to the new 14 pitch prop. If my motor could still spin this new 14 P prop at 5600 RPMs, then I expected to gain 1-2 mph. Well, nothing could be further from the truth. When I installed the new 14 P prop and test ran it, it performed terribly. I couldn't get my RPMs above 4500. Top speed was 23 mph. So much for only losing 200 RPMs per inch of pitch increase. I purchased another Solas aluminum prop that measured 11" dia X 13" P. I figured that this prop would most closely replicate the performance of my old, beat up michigan prop, but without all the dents and dings. When I installed this prop and test ran it, then numbers were better, but not awesome. Max RPMs were around 5400 and top speed was 29 mph. I finally decided to bite the bullet and get a SS prop. I thought the thinner blades would net me a few RPMs, and maybe a few mph too. I bought a Solas SS in 11" dia X 13" P, the same size as my aluminum one. Well, I just ran it today and I was disappointed again. Max RPMs was 5100 and top speed was 30 mph. I can't explain why the RPMs were lower, but they were. I just ordered another SS prop that measures 11.75" dia X 11" P. Hopefully, it won't send my RPMs over 6000. If it does, then I'll have to order a 11.75" dia X 12" P. This is getting expensive! BTW, I guess I have a few props for sale and they are all in mint condition, save the old Michigan. BTW, I ran the motor today without the throttle linkage connected. I used my finger to accelerate, because I wanted to make sure that the throttle linkage didn't need adjusting. Throttle linkage/remote cables are working fine and are adjusted properly. Any ideas why I got such a wide range of results?
*Boat:* 2003 G3 1548 (weight unknown, but it's pretty heavy. I've got 10 gallons of fuel and three batteries on board. Me and my wife weigh 350 combined. Trolling motor, Yeti cooler, side console etc.)
*Motor:* 2012 Yamaha F40 (Runs flawlessly as should be expected from a new motor)
*Manufacturer recommended RPM range:* 5000-6000
*All speed tests were done down and back, with the current and against the current and then averaged to get the most accurate reading from the GPS. I even double checked my Lowrance with a hand held to make sure.


----------



## Johny25 (Mar 31, 2013)

Something with your numbers is surely not correct and I would suspect your tachometer or GPS device. 

Your numbers suggest a slip ratio of this

11X13 original Michigan prop 10% slip
11X14 Solas aluminum 23%
11X13 Solas aluminum 13%
11X13 SS Solas 4%

12-16% slip is what would be typical of an engine this size. The 4% slip reading is impossible on a motor and setup like this and even 10% is an amazing number trust me. The only reading that seams plausible is the 13% number.....and possibly the 23% if way over propped. I would make sure boat had EXACT setup on every run, weight, motor trim, lake conditions etc. But I suspect one of your reading devices is giving faulty readings.


----------



## muskiemike12 (Mar 31, 2013)

You can also play with the motor height to increase the RPM's. I would guess that the Solas props have more cupping and that will decrease RPM's also.
Johnny is right though, 4% slip is impossible for that rig.


----------



## DearJon (Mar 31, 2013)

First of all, thanks for the responses. I agree with you guys. The numbers do not add up. I believe that my tach is working properly. It is a new Yamaha gauge that I installed with the motor. The motor idles at around 700 RPMs, which sounds right. The GPS readings were taken with two different devices. My Lowrance Elite 7 and a hand held Garmin. I do not feel that these devices are inaccurate. Rather, I think that differences in loading, weight distribution and environmental factors (wind, chop) have all contributed to skewed data. So, it's pretty much just me. I'll get out there and conduct some more consistent tests, and report back when I get the results.


----------



## Johny25 (Apr 1, 2013)

Yes there are many more factors involved in this. Cupping shouldn't be much of a factor when it comes to the aluminum props due to the fact most aluminum props have little to no cupping. The SS can and will have better cupping characteristics which can cause loss of rpm (better slip ratio though). I have found in my trials that a typical SS prop will run very similar RPM or just a bit higher than the same pitch aluminum. They have come a long way with aluminum blade design and quality the last 10yrs but SS is still the best when it comes to performance. 

Every manufacturer makes there props different also.....the good thing is you stuck to one manufacturer when buying new props. Try and get your setup the same for each run and see what ya get, multiple passes also to ensure correct readings. I run a 10X14 SS solas on my 30hp johny and it performs very well


----------



## whistler (Apr 2, 2013)

DearJon said:


> ..................... It was an old aluminum Michigan Wheel 10.75" dia X 13" P that was pretty worn and had lots of dings in it. I suspect it might have measured 11" in diameter when it was new. I went out and did all the break in with this prop. After break in, my top speed was 32 mph at about 5800 RPMs. Sounds pretty good, right? Well, I thought that if I bought a new prop, it might do even better. So, I purchased a Solas aluminum 11" dia X 14" P prop.
> ..............................



DearJon with what I know about proping a boat I probably should sit back and listen but I do have a question for you. If your old prop was a 10.75X13 and these are factory numbers on the prop why would you think the prop would be have been 11'' originally (before any wear)? I'm going through some of the same issues. I sure was hoping I could take a prop off your hands but it doesn't look like it would work! Good Luck! 

Just for the sake of playing around have you tried this prop wizard 3.0? https://www.turningpointpropellers.com/


----------



## DearJon (Apr 2, 2013)

Sorry about the confusion. I got the 10.75" number from measuring with a tape, not off the prop itself. I assume that if a prop is used in shallow, sandy situations for many years that continued exposure to the bottom can wear down the tip of each blade slightly. 

And yes, I have tried that prop wizard. I actually think it is one of the better prop selection tools out there, but it's still just a guide. It will likely give you a good starting point, but nothing beats good old-fashioned testing on the water with a GPS and a tach. Well, I guess a GPS isn't really old-fashioned. Thanks.


----------



## whistler (Apr 3, 2013)

DearJon said:


> Sorry about the confusion. I got the 10.75" number from measuring with a tape, not off the prop itself. I assume that if a prop is used in shallow, sandy situations for many years that continued exposure to the bottom can wear down the tip of each blade slightly.



That makes things a lot clearer (at least for me) as to how you arrived at the prop numbers you tried. 



DearJon said:


> And yes, I have tried that prop wizard. I actually think it is one of the better prop selection tools out there, but it's still just a guide. It will likely give you a good starting point, but nothing beats good old-fashioned testing on the water with a GPS and a tach. Well, I guess a GPS isn't really old-fashioned. Thanks.



Agreed! It's a shame that some of us have to go through that much expense to get it right. I'm kind of in the same situation. Again Good Luck!


----------



## Johny25 (Apr 3, 2013)

You know I wasn't paying close enough attention to the size of your boat...... it seems to me that you are over loaded. I tried to find the specs on a 2003 G3 1548 and from what I can tell the boat weighs roughly 400-450lbs and has a weight limit of around 800-900lbs. So if you have 2 adults (350lbs), 3 batteries (150lbs), fishing gear (coolers etc. 50lbs approx), trolling motor (35-45lbs),10 gallons of fuel (70-80lbs) and a 4 stroke 40hp yamaha (213-223lbs) you have to be way over the recommended weight limit. I am calculating all this out to be around 1,250-1,300 lbs total weight! Unless I am missing something regarding the specs on a G3 1548? Also what is the max HP for this boat?


----------



## DearJon (Apr 3, 2013)

Your assumption would be correct. The boat is typically overloaded, even when I fish alone. Also, the boat is overpowered. I know you guys are probably thinking that's a recipe for disaster, but the boat handles quite nicely. I also mitigate any possible risk by having all Coast Guard required safety gear on board, wearing my kill switch and by sticking to the shallows. I'm also not ashamed to admit that I'm a fair-weather fisherman.


----------



## Johny25 (Apr 3, 2013)

Hey your not the first person to run an over powered over weight limit boat. I am borderline overpowered with mine but I am very careful on the over load since I have my children in the boat most of the time. Hell if my boat sinks with the wife and me in it she knows im gonna try and save my motor first ha ha ha.

Anyway the whole point of the overload question was this will effect your performance significantly...especially if your that far over on a narrow hull. You will likely not be able to turn anything over a 13 pitch effectively with that motor, boat style and weight in it. And 32mph is pretty scary that far overloaded on a narrow hull :shock:


----------



## turbotodd (Apr 4, 2013)

https://www.yamahaoutboards.com/sites/default/files/bulletins/bulletin_4stroke_midthrustjetport_al_g3b-eagle165pf-f40tlr.pdf

Most of the performance bulletins I've seen list a 13" or 14". 

Now.....Solas. They are "decent"....cheaper than everyone else and for a reason.

I know a little about Turbo (owned by Yamaha). Turbo propellers take about a month to make each prop. I think 28 days is what I was told. The mold is made, the prop is cast, the preliminary finishing is done....then they are tested by a computer to ensure that it's really a certain pitch before it's all finalized. To my knowledge, they are the only company (or one of the very few) that actually test/verify that each and every prop they manufacture is as close to the advertised pitch, diameter, rake, etc as a prop can get. What I really like about them is that if you buy one from a Yamaha dealer, shipping is absolutely free, from Turbo to the dealership.

The other brands I do not know about. I've run some Solas props and it seemed like one might be a little faster than another, or one might be 200 RPM higher than another....being exactly the same advertised pitch and diameter. Looked like quality control was slightly lacking, and that's probably part of where the costs are cut to keep them cheap.

Finally, overloading is just as bad (actually worse) than underpowering. More hydrodynamic drag. It's entirely possible that you may be at peak performance with what you have. 5500 RPM is about where the F40 "likes" to be, however I like to see them closer to 6000. Choosing a prop that's going to be closer to the 6000 RPM maximum should also give an acceptable holeshot, which could very well be important with your overloaded rig.

Is there any reason you couldn't pick up a new Michigan 3 x 10.75 x 13 to fit the F40?

A coworker of mine has a 2013 War Eagle 1548 (rated for 40 hp) running a 2004 F50 on it. I like the motor because it's 4 cylinder (and SILKY smooth), but not impressed with the performance. 36.3 mph is all we've been able to muster. That's at 5900 RPM and playing with props and motor height. My boat (same exact boat) has an F25, which should be heavy and slow, but it's right at 32, with a 12" SRA prop. Not that much difference if you consider that the F50 is TWICE the power. But it's also 230-some pounds to my 139. Both boats loaded identically for the most part, within about 10 lbs. I even jumped in his and ran it thinking that my lack of body weight would make an appreciable difference. No more than a half MPH. Coworker is 271 lbs and I'm 190.


----------



## DearJon (Apr 6, 2013)

Well, the new prop came in on Friday and I installed it right away. I woke up fairly early this morning determined to get out and run it for a bit before the winds picked up. When I got out on the water, there was just a very light chop, but the wind was already blowing over 10 knts. I managed to run a top speed of 32 mph at 6000 RPMs. That was with the current and a tailwind. Going up current and into a head wind, my best was 29 mph. Maximum RPMs were 6100. I didn't stay at 6100 for more than a second or two. I'll probably keep it around 5500 unless I'm trying to stay ahead of bad weather. With my boat being overloaded, I think this is the best performance I can expect. I'm really happy considering that 30 mph in a 15' tinny is pretty darn fast. BTW, the dimensions on the new prop are 11.75" D X 11" P. Thanks for your input guys.


----------



## Johny25 (Apr 8, 2013)

Well guys I am not trying to be an ass here but the numbers are not adding up. Turbo if you are touching 32mph with that F25 and a 12 pitch then you have to be turning around 6500rpms plus with a 2.08:1 gear case......not impossible but amazing!

And to dearjon..... 6000 rpm at 32mph with an 11" pitch on a 2:1 gear case...... -2 prop slip! The laws of physics makes this impossible. Something is very WRONG here I'm sorry


----------



## turbotodd (Apr 10, 2013)

Johny25 said:


> Well guys I am not trying to be an ass here but the numbers are not adding up. Turbo if you are touching 32mph with that F25 and a 12 pitch then you have to be turning around 6500rpms plus with a 2.08:1 gear case......not impossible but amazing!
> 
> And to dearjon..... 6000 rpm at 32mph with an 11" pitch on a 2:1 gear case...... -2 prop slip! The laws of physics makes this impossible. Something is very WRONG here I'm sorry





.....I didn't say it wasn't on the limiter. And I didn't mention that it's currently running on methanol.


----------

