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JohnMickish

Stainless Vs. Aluminum prop question.

9 posts in this topic

Ok, so can someone tell me what advantage a stainless prop has over an aluminum and vice versa on mid sized motors? Do you run the same pitch on both or does a stainless run differently due to less "flex"?

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the stainless will have less deflection, so more controll. I also think the SST prop will last longer, since its stronger.

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On a midrange setup I think prop/blade flex really isn't that much of an issue.

However, on my boat which is a 16ft Sylvan Pro Select and 90hp Merc, I gain a few mph when I put on the SS prop. I think it's because of number of things.

1. The SS prop is generally thinner on the leading edge and smoother all over, this cuts down on resistance to spin it.

2. The SS prop on my boat has quite different blade geometry than the OEM aluminum and that gives more efficiency and more bow lift. The higher efficiency of the SS prop "grips" the water a little better and the increased lift holds more of the boat out of the water.

3. The SS prop I'm using has ventilation holes in the hub that causes a small-scale, temporary "blow out" that allows the engine RPM to increase more quickly and help with hole shot. IMO, only has much effect if you throttle up very quickly, along the lines of "punch it, Margaret" situations. If you normally ease onto plane, there isn't much benefit to ventilation holes, IMO.

Together these give a noticeable increase in performance for me - if I drive the boat in such a manner to exploit them. YMMV.

If you spend a fair bit of time at WOT and trying to get from point A to point B quickly, or trying to yank skiers out of the water then MAYBE it's worth it. Otherwise, probably not really, but they sure look nice - polished and all...

The advantages to aluminum are cheaper and less likely to damage your lower unit if you hit something with the prop.

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The reason I ask is that my boats prop is not pitched right, 600 rpm short at WOT empty and 1000 rpm heavily loaded. I'm not interested in attaining maximum speed just a better handling boat and thinking that if I go ahead and change props I should look into the difference between the two. I've been to solderbloom.com and have gone thru the prop wizzard and have it figured out to what I should have as far as pitch goes, now I just want to figure out if a stainless is worth the extra cash.

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What size boat and motor do you have?

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1775 Pro V with a 115 Johnson. It currently has a 13X19 aluminum prop on it. 5200-5400 rpm empty/smooth and 4800-5000 rpm three guys full of gear and full livewells.

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I'd stick with the 19p.

SST will help hole shot, top end, handling and control, and won't bend if you bump logs, etc.

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If you are overproped, then go down in size. Afaik, approximately 1" pitch difference changes ~200 RPM. I wouldn't prop for worst case (heaviest load), but opinions may differ on that.

Usually the OEM/dealer guides are pretty close for matching the engine/prop to the boat. It's possible the tach is not quite right, but you need a second that's known to be good for a comparison.

If you want better handling, smoother running, and less steering torque, consider a 4-blade prop. Usually you change pitch-for-pitch, but on the surface, it sounds like you need may to go down a size to 17P (~ +400 RPM) regardless of the type/style of prop.

If you want a fairly cheap experiment, try one of the 4-blade ComProps. I have two and they work fine.

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Quote:

1775 Pro V with a 115 Johnson. It currently has a 13X19 aluminum prop on it. 5200-5400 rpm empty/smooth and 4800-5000 rpm three guys full of gear and full livewells.


You're overpropped. 17" pitch would do nicely on that rig. I'm partial to the turbo line of props offered by Soderbloom.

If you wanna come up to Forest Lake sometime, I'll pull my 13.25x17 turbo off of my boat and you can take a blast around to see how it performs for you.

Tim

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