OK, Prop question for a 1999 Bayliner BR, 3.0L Alpha 1... 3 Blade - 4 blade

[Nohfire53]

On said engine:
1999 3.0L 135HP Alpha 1 pushing a 175 Bayliner BR I currently have a chewed up(rock and sand fish) 14.25x21p 3 blade prop. I am replacing it with a 4 blade as the kids are getting a little bigger and it's all about the tubes and boards now. I have about 600 RPM to play with at WOT. So here is the question:
Which 4 blade would improve my planing at low speed and less effect my top end?

14x20P 4 blade or the wider less slip diameter 14.5x18P?

Thanks for your help,

 

[steelespike]

Re: OK, Prop question for a 1999 Bayliner BR, 3.0L Alpha 1... 3 Blade - 4 blade

What is your present light load wot rpm and speed?The 18 will be slower than the 20.
So are you saying your at 4200 with a typical load?

 

[Nohfire53]

Re: OK, Prop question for a 1999 Bayliner BR, 3.0L Alpha 1... 3 Blade - 4 blade

Yes 4200 WOT typical load, with just me I couldn't tell you, the kids dont let that happen.

the 18P will be slower top end but fast out of the hole correct?

also, the extra .5" diameter should allow less slip and help maintain speed a little better I think, just looking for opinions

 

[steelespike]

Re: OK, Prop question for a 1999 Bayliner BR, 3.0L Alpha 1... 3 Blade - 4 blade

i
If I was putting the prop on a pontoon or other difficult to drive boat or any boat prone to venting or high slip after confirming setup.
It is usual that as pitch goes down diameter goes up. Perhaps with no specific results.A prop is designed to perform as others might
another words a 18 should act like a 18 and so on for other sizes. Of course props have performance personalities that vary
even though pitch might be the same.Then of course the are the rake and cup to consider in prop design.