Alum vs SS prop 20Hp

I fish on the Susquehanna flats, 6 miles X 8 miles. 3'-5' in many places, 6'-12' in some places; really need to know where to go and we all bump bottom. Not a big deal, it's sand. I've always used a SS prop on my 25 Johnson because I thought an aluminum prop would bend first time it churns some sand. I just bought a 20' Tohatsu MFS20 EEFTS. Stock is 9-1/4" X 10-pitch and the blades are welded on the hub. I want to replace with 9-1/4" X 11-pitch. It's going on a 14' Mirrocraft. Are the new aluminum props robust enough to bang bottom? I don't think a 20' 4-stroke has enough stones to turn a stainless prop. What's the board think?

Aluminum props are similar in strength to stainless because they are thicker. Generally the only reason people use stainless is for increased performance due to a thinner blade, which decreases drag and rotating weight. Usually lower hp motors don't use stainless because they don't make much of a difference in performance and are obviously more expensive. An aluminum prop might be painted, so when you flirt with the bottom you may lose paint and it will not look as nice as a stainless if that matters to you. But as far as durability, I'd say they are similar. Both will bend like a pretzel if you hit something.

I have a Mac's river runner bolted to my skeg incase I hit bottom of my rocky bottom river.

aluminum might be "as strong", but I guarantee you that they ding 100x easier

the tips of the blades bend a LOT easier too

The bottom appears to be all SAND, however what's under/in that sand? BTDT cost me a lower unit on a JohnnyRude 9.9 on the Arkansas River (a submerged sandbar)

not all SS props are made the same and not all Alum props are made the same

Tohatsu's stock prop is a piece of junk, or the one I had was (20hp, about 6 years ago). Must be made of 1100, bends real easy, but the good thing is you can pound it back easy too. Dings really easy. Too easy. Blades are thick; so going to SS, you typically stay the same pitch, as long as your max RPM is within reason. This is usually true for small motors. Bigger stuff gets into different territory.

big problem is that not many manufacturers actually make SS props for anything under 25hp. Just one or two is about it. I think Solas does, they're ok but not great. Big blades, give you a lot of thrust sorta like a 4 blade, you'll notice it idling/trolling. No speed increase to speak of, maybe 1mph if you're lucky. Comes out of the hole good, but the big thing is that you can stay on plane at a little lower RPM which is kinda nice. PowerTech makes one as well, little more expensive, and I have no experience with them (SRT series 3 blade, 2.5" gearcase), also available in 4 blade (SRT4). You might call them and see what their suggestions are. Know your maximum RPM currently with the stock prop, you cannot choose a prop without knowing that first. Particularly 4 stroke. They are super sensitive to propping. Miss it by an inch of pitch and the motor will hate you, and you will hate the motor.

Thanks Todd, stock prop is 9-1/4 X 10. I was going to get a Solas SS 9-1/4 X 11. 14' boat weighs 200 Lbs. The Solas is $110 a Power Tech prop is about $235.

u still need to know your current maximum rpm

if for instance your current top rpm is 5900 and the motor's maximum is 6000, going to 11" pitch won't do much, lighten your wallet and potentially slow the holeshot. Remember 4 stroke engines are extremely sensitive to propping, meaning if you miss it by one inch of pitch, you will hate it and so will your entire rig

that said, again, only way to really know is to try it

Powertech's are more expensive because they're better propellers, and made in usa. Solas is chincanese I used to sell a lot of them because people wanted a shiny steel prop but wanted the cheapest one regardless of quality or where it was made or who's kids made it or whatever

I can compare turbo vs solas, to give you an idea (turbo is part of Yamaha)
Turbo makes a run of propellers and checks each one of them for proper pitch vs what it's supposed to be, if it's "off", it goes back into the oven and they make more props with the "scrap". Solas? I have run them in the past and they are rarely the same in that if I take a 10" off and stick another 10" on it, same pitch/dia/spline/etc it might be 100rpm difference, sometimes more sometimes less, like there is just very little attention to qc

also solas ss blades are real thin and they bend easier than I think they should, still stronger than aluminum but I just felt that they bend a little on the easy side. Takes a good lick though.

Max RPM on stock prop is 5650. Engine mounted correctly 2-men in the boat. Trimmed to max. Spec is 5400-6100 RPM. Stock prop is 9-1/4" X 10. When trying to achieve max RPM drop 1" in pitch correct? Looks like a pitch change is the only option. Seems diameter is limited to 9-1/4" by most prop manufacturers.

if you are at 5650 now going to 11" is going to really hurt it, I'd bet you may not even see 5000 RPM.

small motors are different than big motors. WAY different. The 1" of pitch rule doesn't apply to anything under about 100hp.

With two guys in the boat at 5650 I'd be happy with it. Try running one-up and see if you rpm comes up close to the max. If it does you have two choices:

if you run with 2 people on board at all times, you could go to a 9" pitch and that should bring your RPM up to around 6000 or so, which I like to see it as close to "max" as possible. Going over 50rpm won't hurt anything (usually)

if you run with just you in the boat all the time and you are at 5650 with two in the boat, try running by yourself and see where you are at, if close to max as stated above, leave it alone, if u replace with stainless stick with the same pitch (10")

it all depends on how you run most of the time

I keep the stock 10.5" prop in the shop, when the GF goes with me, which is rare, I put it on and pull the 12" off. That way we get on pad quicker and use less fuel, runs close to max rpm with both of us in the boat. With just me in teh boat and 12", it's real close to optimal.

Stocker is 10" pitch. What about keep the same diameter and drop pitch to 9 instead of 10?

I’m familiar with that hull and that motor. I think a 9 is going to be a better prop for you with 2 in the boat. I like the 3 blade solas aluminum, not the best prop, but if you ding it your not out that much. I’ve not tried their stainless props. I’ve gone to Turning point props on my 25. But they don’t make a prop for your motor. I run a river where for about a month out of the year I deal with shallow gravel bars. It tends ding the aluminum some, I wonder how the stainless would do? I think the aluminum would handle sand just fine. Just keep a can of black spray paint handy, if you want it to look pretty.


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