Aluminum to Stainless

[spdracr39]

I read this on another post and have been looking for this answer. Now I would just like a confirmation. Someone said :

"I think if you go to ss you should drop to a 17" Rule of thumb; as pitch increases diameter decreases pitch decreases diameter increases.Diameter is generally only considered in extreme applications like a pontoon."

So question is if you go to a ss prop do you automatically drop 2" in pitch to keep the same performance ?

( I just actually got this answer in another post To slow reading I suppose )

 

[steelespike]

Re: Aluminum to Stainless

The suggested pitch drop was based on the possibility the present rpm was about 400 less than the rating for the motor.You don't a automatically drop pitch when going to stainless.

 

[rallyart]

Re: Aluminum to Stainless

A stainless prop has thinner blades due to the greater material strength. The thinner blades are more efficient in the water so you normally pick up some speed with SS. The pitch gives you the 'out of the hole' power and this is not very affected by the material.
I would not consider that changing the prop material would be a reason to change pitch. Only that some materials are overall better for your application.
I would never consider dropping 2" pitch when I changed from aluminum to stainless, unless I wanted more acceleration and was not concerned with the top speed. Then I would change the pitch regardless of the material I chose.

 

[WIMUSKY]

Re: Aluminum to Stainless

That's the problem. I'm reading conflicting information on multiple threads. When going from aluminum to ss at WOT, do you gain or lose rpms comparing apples to apples, except prop composition? It's been my understanding you gain. Is this true?

 

[Frank Acampora]

Re: Aluminum to Stainless

Because stainless prop blades generally are thinner and flex less, it takes less horsepower just to spin them through the water. Thus, more horsepower is available to drive the boat. So, a stainless prop of the same diameter and pitch, of the same design and manufacturer as the aluminum will generally result in a gain of about 200 RPM at full throttle and about 2 MPH in top speed. --Apples to apples

 

[Snobike Mike]

Re: Aluminum to Stainless

Seems to me that my Volvo SS props are thicker, not thinner than aluminum. The key to SS is they don't flex like Alum and are therefore more efficient at all loads/speeds.