Stainless and RPM's

[Skidz]

I know this has probably been asked before, but my searches did not reveal an answer.

I'm running an aluminum prop right now, 10x13, and my rpm's are perfect at 5480-5520 WOT on my J/E 25. I would like to switch to stainless. Would this have any affect on my rpm's if I keep every thing the same? I was thinking I had read at one time that the rpm's might go down a bit with stainless, but I'm not sure and I can't find it.

TIA,
Skidz

 

[steelespike]

Re: Stainless and RPM's

What is the speed at those rpms?
Going from al to ss is really tough to predict depends on so many points of performance.
I've seen both.
.If your doing ss a dealer may let you try props till you find the right one.
Probably require a sizeable deposit.

 

[Skidz]

Re: Stainless and RPM's

Average about 25-27 with a normal load. 1648 mod-v aluminum jon boat.

 

[Texasmark]

Re: Stainless and RPM's

Would this have any affect on my rpm's if I keep every thing the same?

Problem is, you can't keep everything the same when you make the change. If nothing else, SS blades are much stronger so it takes less to resist the water pressure for a given load. Therefore, by it's very nature, SS blades are thinner and thinking about trying to take a machete vs a baseball bat and slicing the water, which one takes less energy to move....soooo you will up your rpm's which up your speed by definition.

Then SS props are usually cupped which can add the WOT effect of 2" of pitch; may or may not be raked, but on a John, I doubt that rake can do much for you, then there is ventilation and you don't need a ventilated prop on a John....

Mark

 

[Skidz]

Re: Stainless and RPM's

Thanks for your help Mark. If it helps to clarify, I have a Solas 10x13 AL prop now, and I am quite satisfied with its performance. I was thinking of going with the Solas 10x13 SS, and I wanted to understand what if any changes might occur. From your description, it sounds negligible, although I don't want to add too many RPMs, since I am already at the max recommended (5500).

 

[Texasmark]

Re: Stainless and RPM's

Thanks for your help Mark. If it helps to clarify, I have a Solas 10x13 AL prop now, and I am quite satisfied with its performance. I was thinking of going with the Solas 10x13 SS, and I wanted to understand what if any changes might occur. From your description, it sounds negligible, although I don't want to add too many RPMs, since I am already at the max recommended (5500).

If your contemplated replacement SS is cupped, you very well may add 2-3 mph and keep your rpm's where they are. More efficient prop = rpm's up; add 2 inches of cup, loads the engine and pulls the rpm's back down; add cupping effect at WOT means that for the same prop shaft rpm's the "screw" moves forward 2 more inches (theoretically). So a 13" prop with 2 more inches is an increase of 15% so you could expect your 25-27 to go up, possibly to 28-30.

Mark