Aluminum prop for back up

[Rockie69]

OK... I've been reading alot about having a spare prop. So, I have a question and I could be all wet, but here is my logic and I'm curious on what others think.

If I get a spare prop I want to be inexpensive, so the logical thing to do is go with aluminum. BUT, I also want to get the max performace out of my motor, so for testing purposes, is there really that much difference between aluminum and stainless? Once I find a prop size that works in aluminum, wouldn't the same size in stainless be the same?

Example: I have a Solas Lexor 15 1/2 x17 prop (Stainless). If I bought a backup prop say a 14.5 X 19 and I made my boat go 5 MPH faster and brought my RPM's to just under rev. Wouldn't it be safe to say I could go for that same sizes in stainless? (Yes, the 5 MPH is a hypothetical, but I can't let TomS boat be faSter than mine!)

 

[TomS]

Two props that have the exact same advertised pitch and diameter may perform totally differently. Adding the variable of the material, aluminum and stainless, also changes the weight. I'm not a mechanical engineer, but I assume since the weight is rotational not static, it makes even more of a difference for a prop. Also, aluminum flexes a lot more with a 250hp motor than a 90hp motor, so you lose performance there too. ymmv

 

[goldnrod24]

Jared, I'm pretty sure Tom's boat is "fatter" than your boat! LOL.

I've always understood that the reason stainless props perform better is because they tend to flex a lot less than aluminum props. So, the same diameter and pitch prop in each material will perform differently.

That's my story and I'm sticking to it!

 

[Rockie69]

I meant to type PH Phat. I swear I did!

 

[kaydano]

I have a SS and a backup aluminum, and the SS is 2-3 times heavier, and weight would surely be a factor but not sure how much. Once you get up to full RPMs the weight difference may not be noticeable. It probably would be more noticeable on acceleration.

Not sure anyone makes an identical SS and aluminum.