Difference between aluminum and stainless props

[Tinny Fleet]

I have dinged up the aluminum prop on my 1989 2-stroke Evinrude 90 HP, and am thinking of replacing it with a stainless one. The current version is 13x19, which seems to be OK, although not sure if it is optimum..

I remember seeing somewhere that stainless props behave differently than aluminum ones, and wonder if that makes a difference (if true), and if so what difference. Does it change the size of prop I would need?

No ability to test out props, I'll just buy whatever the best choice seems to be and run with it.

Any suggestions appreciated.

 

[Pappy]

Stainless propellers are thinner than aluminum but stronger at the same time. You will definitely gain a bit of speed and economy by going to them.
They can be repaired more often than aluminum. You can normally go up one hole higher on the transom if so desired but not always the case.
Dont drive yourself nuts getting into diameter vs pitch. Go with the same pitch if staying with a 3-blade or go down 1" in pitch if going to a 4-blade. In almost every case you can go up a hole in height with a 4-blade and your out of the hole acceleration will improve as will your cruise speed and economy. In a nut shell thats about all you need to know. Stay with a quality prop manufacturer. Happy Memorial Day!

 

[Tinny Fleet]

Hey thanks Pappy!

 

[thill]

I went from a 19 pitch aluminum to a 19P stainless on my 115 Evinrude, and the difference is outstanding. Somehow, it has a better holeshot AND a better top end. Mine prop is a Raker, by the way. Highly recommended.

 

[Philsfirstboat]

Stainless propellers are thinner than aluminum but stronger at the same time. You will definitely gain a bit of speed and economy by going to them.
They can be repaired more often than aluminum. You can normally go up one hole higher on the transom if so desired but not always the case.
Dont drive yourself nuts getting into diameter vs pitch. Go with the same pitch if staying with a 3-blade or go down 1" in pitch if going to a 4-blade. In almost every case you can go up a hole in height with a 4-blade and your out of the hole acceleration will improve as will your cruise speed and economy. In a nut shell thats about all you need to know. Stay with a quality prop manufacturer. Happy Memorial Day!

Would it make a noticeable difference with a 9.5hp with s 3blade on a 14ft aluminum boat?

 

[airshot]

Would it make a noticeable difference with a 9.5hp with s 3blade on a 14ft aluminum boat?

Not noticable, not worth the expense, typically used on higher hp motors and boats that can exceed 30mph or performance outfits

 

[sonny.barile]

I have dinged up the aluminum prop on my 1989 2-stroke Evinrude 90 HP, and am thinking of replacing it with a stainless one. The current version is 13x19, which seems to be OK, although not sure if it is optimum..

I remember seeing somewhere that stainless props behave differently than aluminum ones, and wonder if that makes a difference (if true), and if so what difference. Does it change the size of prop I would need?

No ability to test out props, I'll just buy whatever the best choice seems to be and run with it.

Any suggestions appreciated.

Just keep in mind that if you are always dinging your prop………the aluminum prop takes the brunt of it. If it’s stainless…..your gear case takes the brunt……..

That being said, stainless is thinner but more rigid, so it flexes less which gets you around 25 more rpm’s. Because the blades are tougher, they are usually cupped a bit more which improves performance in turns By biting more. That’s why it was mentioned that you could go up a hole with your outboard. You will still have a good grip. Getting the motor up higher will add rpm’s…..and it gets the skeg higher which makes less drag. It’s usually a win unless you are always hitting stuff……..If that’s the case reread paragraph 1 of this post. Lol

 

[Pappy]

With the shock absorbing hubs in propellers there really isn't much truth in the old boat ramp saying about gearcase damage while running SS props. Been that way for decades and decades now.

 

[jethro]

Food for thought- I run aluminum on my 150 Merc because it's cheaper to replace a damaged alum prop than it is to even repair it- let alone repair a steel prop. I can get a new alum prop for about $150 as long as the hub kit didn't get damaged. I was told a repair and re-balance would start at $200.

 

[Crazyboat]

If going from Alum. to SS you may have to drop some in dia or pitch as the blades don't flatten out as much and you'll lose some RPM. Also if you dinged up a prop it's not a big deal, if you bust up props and hit something with SS you could damage your lower unit. Something to think about. Always keep a spare prop onboard just in case.

 

[Keith E.]

I went from a 19 pitch aluminum to a 19P stainless on my 115 Evinrude, and the difference is outstanding. Somehow, it has a better holeshot AND a better top end. Mine prop is a Raker, by the way. Highly recommended.

What's your boat?

Thanks,
Keith

 

[thill]

The boat with the 115 is gone, but it was a 17 footer.
I replaced the prop on my 16' Princecraft with a 50 Evinrude, and I went from getting 30 MPH with the aluminum to 36/37 MPH on the stainless prop. The pitch looked too high, but I tried it and it's perfect. Surprising, but good.

 

[airshot]

Are you still within your rpm range ??

 

[Philsfirstboat]

Not noticable, not worth the expense, typically used on higher hp motors and boats that can exceed 30mph or performance outfits

Thanks, money saved can buy more beer!

 

[thill]

Are you still within your rpm range ??

Yes, perfectly Runs from 53-5500, depending on my pitch.

I went from a 15P aluminum that seemed great to a 17P stainless. I did it because I found it in my prop pile and was just curiuos. And because it looked cool. The difference was shocking in a good way. NORMALLY, you go down a pitch for a nice, stainless prop, but in this case, it was up.

Something a prop guy told me long ago was that hydrodynamics is more complicated than it looks, and sometimes it will surprise you. In my years of working on boats, this has proven very true from time to time.

 

[thill]

Buy your plugs at the local auto parts store, like AutoZone, NAPA or Advance Auto. Usually MUCH cheaper than buying from a marina or somewhere online.

I have no idea of the gearcase ratio of that motor, or the weight and water resistance of your boat. You have to start with what you have.

What pitch do you have now, and how does it perform? What is your RPM at top speed?

Take it for a run. With the trim a little on the down side, slowly start trimming the engine up, bit by bit. Your speed should increase each time, until either the bow starts bouncing or the prop starts ventilating (sucking air) Trim it back down just enough to stop and record your speed and RPM.

THAT number will be your WOT (Wide Open Trim) speed as your boat is currently rigged.

Once you know that, IF you are not happy with the performance, post those numbers and others can help you see if a different prop will help.

FOR WHAT IT"S WORTH, sometimes people follow the above directions, and their boat goes faster than it ever has, and they realize that they had just never figured out the best trim angle before.

I hope it works out.