props. stainless vs aluminum.

Been thinking about props a lil. A lil more after seeing a pic in another thread of an obliterated aluminum prop.

If you had two props exactly the same diameter, pitch, and number of blades one black cast aluminum and the other shiny stainless steel would the boat either were on perform the same?

If so why not run the aluminum? It's cheaper to purchase/replace when needed. I'd also imagine cheaper to repair also. I

When you strike the bottom with a stainless the possibility of ruining the shafts and gears in the drive is VERY high. Stainless does not fail very easy. With that said... why wouldn't you run an aluminum prop? The aluminum is soft and when you strike the bottom with one you really just chew up the blades quickly and you save your gear sets and shafts exponentially.

So... is there a performance gain stainless over aluminum? Given my description of the props to choose from and the theory I have presented why wouldn't it be smarter to run an aluminum cheap prop? Does it mearly come down to stainless looking better on a custom boat?

Am I way off here? Whatcha got?

exactly like you said... aluminum is soft, and it flexes. great for hitting things, not too great for keeping it shape under high performance applications.

McRib said:

Been thinking about props a lil. A lil more after seeing a pic in another thread of an obliterated aluminum prop.

If you had two props exactly the same diameter, pitch, and number of blades one black cast aluminum and the other shiny stainless steel would the boat either were on perform the same?

If so why not run the aluminum? It's cheaper to purchase/replace when needed. I'd also imagine cheaper to repair also. I

When you strike the bottom with a stainless the possibility of ruining the shafts and gears in the drive is VERY high. Stainless does not fail very easy. With that said... why wouldn't you run an aluminum prop? The aluminum is soft and when you strike the bottom with one you really just chew up the blades quickly and you save your gear sets and shafts exponentially.

So... is there a performance gain stainless over aluminum? Given my description of the props to choose from and the theory I have presented why wouldn't it be smarter to run an aluminum cheap prop? Does it mearly come down to stainless looking better on a custom boat?

Am I way off here? Whatcha got?

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I think that you bring up a very good point.

Aluminum props flex at high speed and load so you get less pitch at higher speeds

mjc said:

Aluminum props flex at high speed and load so you get less pitch at higher speeds

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Obviously for the guys with long legs aluminum is not the best choice. I'm talking more about the guys 25 ft or less with 400 HP and less. Every custom boat from 19 to 25 ft made for the past 15+ years with a bravo drive has come with a 6 to 900 dollar stainless prop. I have a 23 footer 496 B1 and I'm good for no more than 60 mph on a good day. Do I really need a 800 dollar stainless prop when I can get a 250 dollar aluminum direct replacement? Do any of the boats in my range need a stainless prop? Other then it looks better on the trailer I gotta say no. Guys with blue motors and 80 mph cruising speeds I can see stainless being the only option but guys like me and smaller.... I'm thinking not.

This is preemptive.

No! I have not tried a different prop...... yet.

ka0tyk said:

exactly like you said... aluminum is soft, and it flexes. great for hitting things, not too great for keeping it shape under high performance applications.

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That is the answer. Performance. If you get into sand aluminum is no bueno, stainless takes a lickin and keeps on tickin. I would not go higher than 4200 -4500 rpm with aluminum.

Aluminum have to be considerably thicker than stainless, so even before you deal with the flex issue, it is less efficient.

Aluminum is good for small blocks if you find your overloaded 20 foot boat at higher altitude (like Lake Powell) and you can't get the fat kid out of the water on a single ski......

I bought a lower pitched 3 blade aluminum prop at the Wahweap Marina for under $100 and it solved the problem. I ran the same prop at Havasu and my over-rev buzzer was going crazy in a couple minutes, so I switched back to my 4 blade stainless. I kept it on board for a spare but never used it again.

Both are typically cast. SS is just a stronger material. It is harder to weld and machine but its durability is far superior to even the best billet alum in the long term. To buy, machine and maintain a billet alum prop would far out weigh the costs of a SS version. It is fiscal sense. Fiscal sense is probably why we are not seeing titanium props. They use titanium for turbines as cost is not the main factor, safety is. In the middle is bronze, but that is not the subject matter here.

I have the same size 4 blade props for my toon in both aluminum and stainless. The stainless has much better performance from hole shot, top end and bow lift. Of course the blade shape is much different with the stainless having aggressive cupping. The aluminum will easily turn 400 more RPM without any noticeable gain.
We run the river below Parker. Water levels average 4-5ft. and can change quickly. The aluminum has become a sacrificial prop. It has been repaired 3 times this season. A new aluminum prop can be had for what it costs to repair a stainless.

If you had two props exactly the same diameter, pitch, and number of blades one black cast aluminum and the other shiny stainless steel would the boat either were on perform the same?

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No. The aluminum does not have the strength of SS, and thus requires a thicker blade to withstand the stress. A thicker blade can be less efficient. The blade will also abrade or wear faster. As others stated the pitch tends to flatten out under heavy load thus decreasing pitch.

I'm talking more about the guys 25 ft or less with 400 HP and less.

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I would not run more than 220 hp through an AL prop.

I have a 23 footer 496 B1 and I'm good for no more than 60 mph on a good day. Do I really need a 800 dollar stainless prop when I can get a 250 dollar aluminum direct replacement?

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You won't likely do 60 without your stainless prop. In addition you cannot get a direct replacement prop for your stainless in aluminum. For instance, suppose you have a Mirage 3 blade and replace it with a 3 blade aluminum (Quicksilver etc). Other than both props having 3 blades it is not a direct replacement. The blade design, rake, cup, blade area etc are all different. Even IF the pitch and diameter were the same, and rake for that matter, the blade design and blade surface area will be substantially different giving you different performance. They don't make, and virtually can't make the same blade design of a stainless prop in aluminum simply due to aluminum's weaker strength.

You don't need to buy a new $800 prop. Most new stainless are $500-600 (yes I know there are some the cost tons more, but in general...) Don't buy them new. Get them used. I have had 4 stainless props and haven't paid more than $300 for one. Cheapest was $200. All were/are in great shape and Mercruiser products, not some off brand stuff.

One other consideration, especially since you have a big block. If you run an aluminum prop it will likely vibrate noticeably under load due to stress pitch imbalance. The loaded blades will flex at different rates hampering performance and cause vibration.

Having said all that, strap on an aluminum and report back.

McRib said:

No! I have not tried a different prop...... yet.

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And now?

TBI said:

And now?

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2 weeks

McRib said:

2 weeks

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they still make aluminum props?