20SC w/ 115 #'s and opinions needed

[McGillicuddy]

Originally Posted by Bushwacker

Gillie,

My experience, at least with Michigan props, is that they're able to make the blades thinner on the SS props, so they're actually EASIER to turn than the same size aluminum. When I started trying 4 blade props, the local shop recommended a 14" dia x 20" pitch aluminum Vortex prop. The equivalent SS prop was the 4B Apollo, but they made it slightly bigger at 14.125" diameter x 20" pitch, I guess to compensate for the thinner blades. I could turn both props to the same rpm with same load, but the SS prop was about 3 mph faster!

When I was running the old 115 on my boat, the 13 3/4 x 15p OMC SST prop turned about the same rpm as the same size aluminum prop, but the SST had a lot more cup in the trailing edge. I was able to raise the motor 1 hole and also picked up about 3 mph with the SST. It was an excellent prop and the 15x15 4B SS PowerTech prop I'm now running supposedly has the same blade profile as the old SST. The 15x15 4B prop seems to be very efficient and runs about 4-5% slip at optimum cruise! Denny

Denny,
Thanks for sharing that experience. Duly noted. Theoretically, the ability to make blades thinner, should make them easier to turn. I think where maybe it gets tricky is that the finer casting makes more complexity available to the shape thus they can use more cup or rake in a similar geometry to improve the desired performance characteristics. Between that and the added weight varying models may or may not prove harder to turn.

Interesting that the Vortex/Apollo actually increases the diameter in stainless.

When I asked PowerTech about replacing my Black Max with their stainless equivalent (MQF series) they suggested dropping an inch of pitch even though they share the same diameter and approximate blade profile. That was the basis for my suggestion to Mike. A have not tried the stainless MQF version yet. And again they are not "identical" - my guess is that PowerTech has tweaked the design a bit.

Cheers,
Gillie