Stainless vs Aluminum Prop Question Evinrude 35hp

I have been trying to get a little more performance out of my jon boat. It has a 1981 Evinrude 35hp and the boat is a heavy 16ft 1972 polarcraft. I added a big casting deck out of plywood, bow trolling motor, storage compartments up front for tackle. the Troller is 24v system and i don't have enough room for both batteries and gas tank back by the transom so one of the batteries is about mid point of the boat on the side. I first added a CMC pt 35 and thought i might get a little speed out of it, but after playing with engine heights i'm still getting about the same performance.

I am currently running a 10.5x11 solas aluminum prop and it turns about 5400 rpm WOT with just me in it and i get about 25.5 mph. I have two 10.5x13 pitch aluminum props that run about 4600 rpm WOT.

I am wondering if i went stainless if i could get any more speed out of it? I am sure if i redistributed the weight in the boat i could help it out that way but i like my layout the way it is. I swear i saw a thread somewhere of someone testing various pitches of both stainless and aluminum on a similar setup and found that he had significant performance improvements with the stainless and I believe he was also able to go up a pitch but i can't find that thread anywhere now. Ideally i'd like to get up to the 28+mph range, which sounds insignificant but when you are fishing the Mississippi river with miles of backwater it would help to extend my fishable range.

Agreed on skipping a SS option, but check out that prop calculator & see if Turning Point has one of their new ‘pressed’ aluminum4-blade props for your motor.

I rigged three 14-16’ boats pushing heavier loads w/ those new 4-blade props and the performance was exceptional! One was my own boat and it would JUMP up on plane.

That's pretty good speed for the load.

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Would your 35hp cover fit on a 50 hp motor?

A stainless 13P prop " might " get you to 28mph and keep the rpm at 5400ish.. the rule of thumb is you can go up one pitch size and stay at the same rpm.. but not many have done this with small motors so it's a $200 gamble.
I'm debating doing the same on my 16ft/30hp/11P once I get $300 cdn. That I don't know what to do with.. lol

GYPSY400 said:

A stainless 13P prop " might " get you to 28mph and keep the rpm at 5400ish.. the rule of thumb is you can go up one pitch size and stay at the same rpm.. but not many have done this with small motors so it's a $200 gamble.
I'm debating doing the same on my 16ft/30hp/11P once I get $300 cdn. That I don't know what to do with.. lol

Click to expand...

You must have a bent thumb........Have never heard of this particular "Rule of thumb"
Simple physics, if nothing else, dictates that as you increase pitch your RPM will go down.

Pappy said:

GYPSY400 said:

A stainless 13P prop " might " get you to 28mph and keep the rpm at 5400ish.. the rule of thumb is you can go up one pitch size and stay at the same rpm.. but not many have done this with small motors so it's a $200 gamble.
I'm debating doing the same on my 16ft/30hp/11P once I get $300 cdn. That I don't know what to do with.. lol

Click to expand...

You must have a bent thumb........Have never heard of this particular "Rule of thumb"
Simple physics, if nothing else, dictates that as you increase pitch your RPM will go down.

Click to expand...

Ha ha!! No my thumb is straight.. the reason this works with a stainless prop is because the blades are thinner than an aluminum with the same pitch - Therefore less drag..
Like I said though, it's a gamble because there is not a lot of documentation on the smaller motors.

This is an interesting topic. I have read a lot about props on small outboards but haven't done any experimenting. It's tough to buy a $300 prop for a motor you paid $400 for. I currently run a 1983 Johnson 35 on a 16' Naden vee hull. It's a utility boat with no extras except for a single battery and a trolling motor. Factory 10x13 with a couple minor dings I can get 26-27 alone and 24-25 with one guy and 20- 22 with 3 of us (all of us are 225 give or take 10lbs)
There is a trolling plate on the motor which may hurt top speed a bit. Motor is jacked up on the transom with a spacer but does not blow out.

I know with the larger engines, a stainless prop will be faster and holeshot better due to less flex on the blades. As a result, a stainless prop should be a pitch lower to keep ROMs where they should be. This was the case on the ski boat. I haven't found any tests done with sub 40hp outboards. If you have, please share it here.
I'm going to stick with aluminum for the price and also because there are alot of rocks where I fish and I have smoked one before and been back in business with some gentle hammer tapping. If I do buy a prop, I think I'd try a Solas 4 blade in 10x13. They say the blades flex less because they're smaller and more of them..not sure how much flex happens with a 30 HP outboard pushing 1000lbs.

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GYPSY400 said:

Pappy said:

GYPSY400 said:

A stainless 13P prop " might " get you to 28mph and keep the rpm at 5400ish.. the rule of thumb is you can go up one pitch size and stay at the same rpm.. but not many have done this with small motors so it's a $200 gamble.
I'm debating doing the same on my 16ft/30hp/11P once I get $300 cdn. That I don't know what to do with.. lol

Click to expand...

You must have a bent thumb........Have never heard of this particular "Rule of thumb"
Simple physics, if nothing else, dictates that as you increase pitch your RPM will go down.

Click to expand...

Ha ha!! No my thumb is straight.. the reason this works with a stainless prop is because the blades are thinner than an aluminum with the same pitch - Therefore less drag..
Like I said though, it's a gamble because there is not a lot of documentation on the smaller motors.

Click to expand...

Fallacy. :roll:

If they were that much more efficient there would be no such thing as an aluminum prop.

In reality the inverse of your assumption is true.

The same pitch SS prop will lower your RPMs as it is working harder due to less flex.

Weldorthemagnificent said:

This is an interesting topic. I have read a lot about props on small outboards but haven't done any experimenting. It's tough to buy a $300 prop for a motor you paid $400 for. I currently run a 1983 Johnson 35 on a 16' Naden vee hull. It's a utility boat with no extras except for a single battery and a trolling motor. Factory 10x13 with a couple minor dings I can get 26-27 alone and 24-25 with one guy and 20- 22 with 3 of us (all of us are 225 give or take 10lbs)
There is a trolling plate on the motor which may hurt top speed a bit. Motor is jacked up on the transom with a spacer but does not blow out.

I know with the larger engines, a stainless prop will be faster and holeshot better due to less flex on the blades. As a result, a stainless prop should be a pitch lower to keep ROMs where they should be. This was the case on the ski boat. I haven't found any tests done with sub 40hp outboards. If you have, please share it here.
I'm going to stick with aluminum for the price and also because there are alot of rocks where I fish and I have smoked one before and been back in business with some gentle hammer tapping. If I do buy a prop, I think I'd try a Solas 4 blade in 10x13. They say the blades flex less because they're smaller and more of them..not sure how much flex happens with a 30 HP outboard pushing 1000lbs.

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Click to expand...

25%+- for aluminum VS 10%+- for SS.

This thread has some good real world info on props near the end and is an interesting read overall.


https://www.boatracingfacts.com/forums/showthread.php?15576-Evinrude-31-8ci-Mod-Advice

Interesting read. I think I'll leave mine stock and run it for a few more years. Lol. I'm just a fisherman but the top end speed is fun as well.

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GYPSY400 said:

Pappy said:

GYPSY400 said:

A stainless 13P prop " might " get you to 28mph and keep the rpm at 5400ish.. the rule of thumb is you can go up one pitch size and stay at the same rpm.. but not many have done this with small motors so it's a $200 gamble.
I'm debating doing the same on my 16ft/30hp/11P once I get $300 cdn. That I don't know what to do with.. lol

Click to expand...

You must have a bent thumb........Have never heard of this particular "Rule of thumb"
Simple physics, if nothing else, dictates that as you increase pitch your RPM will go down.

Click to expand...

Ha ha!! No my thumb is straight.. the reason this works with a stainless prop is because the blades are thinner than an aluminum with the same pitch - Therefore less drag..
Like I said though, it's a gamble because there is not a lot of documentation on the smaller motors.

Click to expand...

Yet another fallacy !! When the first words of of a ramp guru's mouth are "Well I heard........" just let it go in one ear and out the other.

When you switch from an aluminum prop to a stainless of the same pitch and manufacturer you stand a good chance of increasing performance due to blade thickness and design but not when you go up to the next pitch in stainless vs. a lower pitch aluminum. Different ball game.

Pappy said:

GYPSY400 said:

Pappy said:

You must have a bent thumb........Have never heard of this particular "Rule of thumb"
Simple physics, if nothing else, dictates that as you increase pitch your RPM will go down.

Click to expand...

Ha ha!! No my thumb is straight.. the reason this works with a stainless prop is because the blades are thinner than an aluminum with the same pitch - Therefore less drag..
Like I said though, it's a gamble because there is not a lot of documentation on the smaller motors.

Click to expand...

Yet another fallacy !! When the first words of of a ramp guru's mouth are "Well I heard........" just let it go in one ear and out the other.

When you switch from an aluminum prop to a stainless of the same pitch and manufacturer you stand a good chance of increasing performance due to blade thickness and design but not when you go up to the next pitch in stainless vs. a lower pitch aluminum. Different ball game.

Click to expand...

I did a little more research on the subject (5 minutes on Google!)
Stainless does have benefits, but on small motors it would be hardly noticeable..i found this video from a reputable source https://youtu.be/8t3L6GUB-uU

My statement on pitch was false and I stand corrected... you don't get a pitch for free but the slight increase in performance would make it "seem" so.

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