stainless or aluminum?

I run shallow rivers, mostly sand bottom, but does have timber and rock on occasion. I have a Merc. 20 hp 4 stroke on a crestiner 1648. Is a stainless more durable or am I encouraging possible bent shaft issue?

Bob.

my 2 cents, the aluminum will be far more forgiving if (WHEN) you hit something. Maybe get a decent used one just for that application?

You should look into getting a prop protector for your motor. I have a Mac's River Runner on my motor.

Bottom line is that you can bend a propshaft regardless of propeller material. Benefits of aluminum are that they are cheap to replace. Benefits of stainless are that you can rebuild them many more times than aluminum and will give you better performance. Both have a rubber hub designed to slip and/or fail long before you bend a propshaft. Old wives tail on the stainless shaft bending.

On a 20 hp motor you are not going to get that much better performance from a SS

Go with the aluminum -cheap and you can get several; for the price of a SS prop


If you had a larger engine that I would go with SS

I will humbly disagree with "not going to get much better performance with an SS on a 20hp motor". I read these same arguments from people when trying to decide if I should go with a SS on my 30hp motor. Nobody could produce hard evidence to prove these claims so I purchased 2 different SS props and compared them to the 3 stock aluminum props I have and the upgrade in performance was substantial. The SS props perform better in every way possible from hole shot, planing at a lower RPM and overall top speed. I meticulously recorded difference in RPM and GPS readings on all the props and the SS's won hands down. I have heard that HIGH end aluminum props do perform like SS props but I cannot confirm nor deny since I have never tried them. I figured if I was going to spend extra to get the SS.

And I will agree with pappy, the hub should slip first weather aluminum or SS. IMO it is worth the extra $100 or so for an SS prop

I wouldn't count on the hub slipping before major damage to your lower unit is done. Aluminum is more forgiving for the lower unit than SS when it comes to hitting objects.

I will humbly disagree with "not going to get much better performance with an SS on a 20hp motor". I read these same arguments from people when trying to decide if I should go with a SS on my 30hp motor. Nobody could produce hard evidence to prove these claims so I purchased 2 different SS props and compared them to the 3 stock aluminum props I have and the upgrade in performance was substantial. The SS props perform better in every way possible from hole shot, planing at a lower RPM and overall top speed. I meticulously recorded difference in RPM and GPS readings on all the props and the SS's won hands down. I have heard that HIGH end aluminum props do perform like SS props but I cannot confirm nor deny since I have never tried them. I figured if I was going to spend extra to get the SS.

And I will agree with pappy, the hub should slip first weather aluminum or SS. IMO it is worth the extra $100 or so for an SS prop

Click to expand...

I second this with testing & racing done on them.

Johny25 said:

I will humbly disagree with "not going to get much better performance with an SS on a 20hp motor". I read these same arguments from people when trying to decide if I should go with a SS on my 30hp motor. Nobody could produce hard evidence to prove these claims so I purchased 2 different SS props and compared them to the 3 stock aluminum props I have and the upgrade in performance was substantial. The SS props perform better in every way possible from hole shot, planing at a lower RPM and overall top speed. I meticulously recorded difference in RPM and GPS readings on all the props and the SS's won hands down. I have heard that HIGH end aluminum props do perform like SS props but I cannot confirm nor deny since I have never tried them. I figured if I was going to spend extra to get the SS.

And I will agree with pappy, the hub should slip first weather aluminum or SS. IMO it is worth the extra $100 or so for an SS prop

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How much better - how much did the same prop (same pitch and blades) in SS v. Aluminum increase your MPH with a 20 hp motor?


I would think that the amount of flex in a aluminum v. a SS with a smaller engine would not equate to a vast loss of performance vs. the cost difference (roughly 1/3 the price for aluminum)


I hope that I am wrong as I keep looking at a SS prop but purchased three different aluminum ones instead to try some stuff

Ok I never tried it on a 20hp, mine is a 30. And I do agree that the flex is not really an issue at this low of HP. The performance differences I believe come from a couple other areas.

1. thinner blade allows it to spin faster and easier (even though it weighs more than double)
2. blades can have more cup and better design due to material. On all aspects of the blades.

I found that I can turn a prop of 1 pitch higher in SS at the same RPM as the lower pitch aluminum. This can be backed up on plenty of prop forums. Turning a higher pitch at a higher RPM gained me between 1.7-2.2 mph on top end with a light load in the boat and 1.8-2.5 mph when I had a real heavy load in the boat. I could also keep my boat on plane almost 400rpm lower than any of the aluminum props. Now 2mph may not sound like much if your talking 100mph but when we are talking 25-30mph ranges that is a significant gain in my book. This is just info that I found and tested first hand and will not guarantee anything. But I would not give out false info either.

Higher RPM at a higher pitch= better performance

Thanks Johny - that is a significant gain (especially as an overall percentage)

This is what I wanted to hear.. I've been toying around the idea of buying a SS prop.. My buds have been saying its a waste of money on a small 30hp

Johny25 said:

Ok I never tried it on a 20hp, mine is a 30. And I do agree that the flex is not really an issue at this low of HP. The performance differences I believe come from a couple other areas.

1. thinner blade allows it to spin faster and easier (even though it weighs more than double)
2. blades can have more cup and better design due to material. On all aspects of the blades.

I found that I can turn a prop of 1 pitch higher in SS at the same RPM as the lower pitch aluminum. This can be backed up on plenty of prop forums. Turning a higher pitch at a higher RPM gained me between 1.7-2.2 mph on top end with a light load in the boat and 1.8-2.5 mph when I had a real heavy load in the boat. I could also keep my boat on plane almost 400rpm lower than any of the aluminum props. Now 2mph may not sound like much if your talking 100mph but when we are talking 25-30mph ranges that is a significant gain in my book. This is just info that I found and tested first hand and will not guarantee anything. But I would not give out false info either.

Higher RPM at a higher pitch= better performance

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GREAT ANSWER!

Ok here is the data that I took on the props I ran and tested. When I bought my motor it had a 10.5X11 stock OEM prop. My 1988 30hp johny has a recommended RPM range of 5200-5800. And 5500 rpm is where it produces max HP. The object is to get as close to the top of your RPM range. So here it is : )

Heavy load in my 14' boat: 1,150lbs total weight
10.5 X 11.......stock aluminum..........6010 RPM (did not have GPS at this time)
10.13 X 11.....SS Cabela's prop.........6290 RPM (took it off and never ran it again) Way to high!!!!
10 X 13..........stock aluminum..........5450 RPM......25.7-26.4 mph
10 X 14..........SS New Saturn Solas....5400 RPM......27.4-28.2 mph
10 X 15..........stock aluminum..........5030 RPM......25.2-25.7 mph

Light load: 875-900lbs total weight (did not run either of the 11 pitch because they were to high of RPM with heavy load)
10 X 13...........stock aluminum..........5800 RPM.....28.0-28.5 mph
10 X 14...........SS Solas......................5730 RPM.....29.6-30.2 mph
10 X 15...........stock aluminum..........5350 RPM.....27.8-28.1 mph


And what I got from all this data other than a headache and a lighter wallet was that stainless steel outperforms aluminum hands down. And maybe it only happens on my motor.....lol. But this is the info I gathered so interpret it anyway you choose to.

I did reach a speed of 31.8mph with the Solas 14 SS when I jacked my motor up 2.25 inches but I had water spraying all over out the back and did not like it. The prop would also blowout way to easy in turns so after several different engine height adjustments I just put it all the way back down on the transom where I did all my testing and called it good.

Great stuff Johny - but you are running different pitch SS and Alum props? Kinda not apples to apples if you know what I mean.

I am not trying to bust your balls about this - i understand what you are saying and i think you are 100% correct, just trying to learn a little

Well I never ran a 14 pitch aluminum correct. But I did run an 11 pitch aluminum and stainless. The RPM difference was 280. Ok now look at the RPM between the 13 aluminum versus the 14 stainless. The RPM's were virtually identical but the 14 is obviously 1 pitch higher, hence the better performance.

And like I stated to start with, if you can turn a higher pitch at a higher RPM you will get better performance and that data right there proves exactly what I stated. If I would have had GPS when I ran the two 11's there would have been a speed difference also. You could feel it in the boat between the two 11's also. Not just me, but the other 2 people in the boat could tell the difference also. I understand that you are just pointing out that I did not run a stainless in every pitch versus aluminum but come on who has the money to actually do this lol...... I have a family to support and it ain't coming from propellers :lol:

If you don't see performance benefits from stainless in that data well then you would fit right in with the people in the government who balance our budget..... :lol:

Thanks - great info


I will likely get a stainless at the same pitch as one of my Aluminum props and then give it a try

I was just giving you a hard time Ahab But yeah I would recommend a stainless if you want a little more performance. Some people could care less but to me I figure the SS will pay for itself in fuel saved in about a year's worth of use : )

If I can get there faster with the same RPM's as an aluminum then I run my motor for less time which equates to fuel and money saved. And fuel nor 2 stroke oil is cheap so it adds up quick.

The hub is not designed to slip. If it does, it has to be replaced. It is a dampener that dampens sudden changes in load, whether it be a rock, stump, shifting into gear, whatever. Once it spins inside the prop, it should be replaced as it will continue to spin. Some of the newer easily replaceable hubs are square shaped. They still do the same job but they can't spin inside the prop itself; rather the splined insert spins out of the rubber. Solas Rubex is a good example. Those can be replaced easily without anything but a prop wrench and a plier.

There is a small difference in performance with SS, however, the smaller the engine, the less difference there is. Where the difference lies is in those who are attempting to get EVERY tenth of a MPH out of a little engine. Now bigger motors are a different ballgame altogether. On a 150, comparing a stock cheapie aluminum prop to a good SS prop, there might be 3-5 mph difference. But most of the small motors I've messed with (25 and under) 1-2 mph at most, unless the motor is running high on the transom and blowing out with the non-cupped aluminum prop. In that type application a good SS with some cupping would help a TON.

SS being harder on parts is a old folk tale. I would be willing to bet that more prop shafts and gearcases are/were damaged by folks using an aluminum prop than those with SS.

For a 150hp motor to get the same performance increase from an SS as a 25hp it would have to perform 6 better correct? Meaning if the 25hp gets a 1-2mph boost in performance the 150hp should get 6-12mph boost, but we know this is typically not the case and as you have stated (and I agree) 3-5mph increase is more likely. So in reality the 25hp benefits HP for HP more than the 150hp running a stainless.