Rake vs pitch

[Barnacle_Bill]

I recently had to buy a new prop to replace my damaged one. I needed to get RPMs down as they were too high. He didn't have a 23 pitch but loaned me one the same size as my old merc prop but with a lot more rake. I was amazed as it lowered my RPMs by about 300 revs and ran a lot better at WOT. I lost some on my hole shot and since I could stand a little lower RPMs, he put a cup in it. I now have a great running prop. This caused me to wonder when it would be better to recommend more rake rather than more pitch to get RPMs down a few hundred RPMs. Any insight? BTW its amazing how they put a cup in the prop. I expected to see a fancy hydraulic machine instead of a hammer and a hunk of steel.

 

[JCF350]

Re: Rake vs pitch

Rather than typing a lot I'll be lazy.

boatinglife.com/article_content.jsp?ID=37439

Used to cup props on the motor with 2 ball peen hammers (You swing both so they make contact at the same time). It's all in the technique.

 

[Bondo]

Re: Rake vs pitch

Ayuh,......

I'd sooner think that your Lowered rpms is from the added Cupping,.....
And,....
Not the amount of Rake........

 

[Barnacle_Bill]

Re: Rake vs pitch

Ayuh,......

I'd sooner think that your Lowered rpms is from the added Cupping,.....
And,....
Not the amount of Rake........

He told me the rake would bring it down and it did. I took it back for fine tuning and thats when he added the cup.

 

[HighTrim]

Re: Rake vs pitch

I was always told the cupped propeller of the same pitch and diameter will typically reduce your RPM by approximately 200.

 

[Esox]

Re: Rake vs pitch

bogerprops.com/PitchandRake.html