I really need some help selection the correct prop!

[tmaysjr]

Current boat and prop: 22.5 foot deckboat with a 260 horse 5.0L MPI mercruiser second gen. Alpha I. WOT is 5000 RPM at 47 MPI on my 3 blade alum. 17 pitch prop.

When I get a bunch of folks on the boat it does not plane as quickly as I would like and really does not pull skiers as I would like, so better hole shot is important. Also, I have notices what I think is cavitation when I turn.

I was thinking about a 4 blade, SS 17 pitch.

Any input, opinions or suggustions would be greatly appreciated.

 

[craze1cars]

Re: I really need some help selection the correct prop!

What is your gear ratio? If your tach is accurate, you are very well propped for pulling, right at 5,000 rpms...

Generally speaking, switching to a 4 blade stainless might improve holeshot performance a bit over your 3 blade aluminum, but it might also reduce your RPMS if you stick with the same pitch, which reduces HP output at take-off, which might negate any benefit from the improved bite.

So I wouldn't be surprised if you need to go down to a 16 or 15 pitch if you change to stainless 4 blade, in order to maintain your rpms.

 

[tmaysjr]

Re: I really need some help selection the correct prop!

Thank you for the help. I dont know what my gear ratio is. would a 3 blade 17 pitch SS prop help things much or should I stick with replacing exactly what I have?

 

[Bifflefan]

Re: I really need some help selection the correct prop!

A 17p 4 blade will make the issue worse not better.
When you use a 4 blade you need to drop one inch in "p" to keep it the same, with that in mind would need to go to a 15p 4 blade to get a one inch drop. I have only seen even numbered "p" in 4 blade props so that would put you at a 14p prop. That's not much. I'm more inclined to think your motor is not running well enough. Its probably time for a cap, rotor, plugs, and wires.