Prop Diameter Question

[scsims]

I'm looking at 2 different props one is a Apollo 13x21P and the other is a Rapture 13 1/4x 21P.<br /><br />Will there be any difference in running these props? Will the Rapture have slightly lower rpms due to it being a 1/4" bigger?

 

[walleyehed]

Re: Prop Diameter Question

The RPM may be different, but not because of diameter....it would be because of 2 different prop designs.<br />From what I can tell right now, the Apollo should give a bit more bow lift than the Rapture, but because the Rapture has a "bit" more diameter, you may be able to raise the engine a hole and actually increase rpm.

 

[scsims]

Re: Prop Diameter Question

What exactly is bow lift?

 

[walleyehed]

Re: Prop Diameter Question

Bow lift would be a prop with high Rake (Blades lay back more than others) and the cup of the prop is built-in in a specific area, such as continued around the tip, maybe not just the trailing edge, to help "lift" the front (Bow) to increase speed (efficiency).<br />Some boats need bow-lift some need stern-lift, some do best with an over-all lifter. I'd say "most" SS props are over-all lifters, falling slightly higher on the side of bow-lift.