3 vs 4 blade

[nsh_dirty30]

I have a 18' Campion w/ aluminum 3 blade 21p x 14.25'' and @ WOT I get 4400 rpm ( 3800-4200 suggested) at a top speed of 48 mph. If I were to go to a SS 4 blade how much pitch would I need to drop to and still keep my 4400 rpm? I'm hoping a 4 blade will give me better fuel economy at cruise!

 

[walleyehed]

Re: 3 vs 4 blade

Clarify the boat type if you would, please....

 

[nsh_dirty30]

Re: 3 vs 4 blade

It is a 18' Campion Hardtop, closed bow. weighs 2050 lbs

 

[walleyehed]

Re: 3 vs 4 blade

Not knowing the prop model you have, you should be in the ball park with a 20P 4bld SS. A Stiletto Bay Pro II is about as good of all-around design you can get. I don't know what type of powerplant you have and that may come into play in choosing a prop.

 

[Brewman61]

Re: 3 vs 4 blade

I did a similar swap. I have an 18' fiberglass bowrider (crownline). It has the 4.3 MPI and alpha Gen II.
I was using an AL 3 blade 21P with a 14.25" diameter. I went to a 4 blade SS 19P @ 14" diameter.
Swap worked perfectly for me. Much happier with the performance.
The suggestion to go from the 21P to the 19P with this prop was from the seller.

Many prop dealers have a swap program, where you can switch one prop for an identical one of a different pitch. You could see if you have that available, sometimes you just won't know for sure till you run.
The swap program I had was only available for SS props, and you had to return your prop in a certain time frame, undamaged of course.

 

[Texas Parrothead]

Re: 3 vs 4 blade

Brewman - Did you get a better hole shot with the new prop and did it seem "smoother" at cruise? Also did you loose any top end at cruise?

Thanks, i am looking to make the same change you did.