Prop selection for 22' Cruiser 260HP Alpha One

[mguidry629]

I've had the boat about a year, but just got it running last fall and just now starting to really get it going and start tweaking things.....

1987 Chris Craft 230 Limited 2800 lbs dry (add about 1000 for people and gear + 80 gallon tank)
5.7L Mercruiser 260 (1.5 gear ratio Alpha One)

Current prop is a 13 3/4" x 21p Mercury part # 48-73982A4 (I think it's had some work done to it though)

My last couple of trips out I've been taking notes on RPM / Speed output

2 weekends ago, 2 adults and 2 kids, about 3/4 tank of gas: 3400 RPM = 38mph and top speed 4200RPM = 45mph

Last weekend, 4 adults and 2 kids, full tank: 3400rpm = 35/36mph and about the same top end 4200 @ 44/45mph

As to be expected, I was not quite as efficient with the extra weight of 2 more adults and about 20 more gallons of fuel.

A friend of mine has a couple Mirage Plus props in 17p and 19p that I'm going to try out. I also have a 14 x 19 Michigan prop to try. I know the Mirage Plus is over 15" diameter and designed for more HP than I have, so is it worth trying these out? Should I try the 17p or 19p first?

Any other suggestions of prop styles? I'm trying to get the WOT at 4600-4800. And hopefully increase my hole shot (which is terrible w/ the 21p), overall efficiency and top speed.

 

[mguidry629]

Re: Prop selection for 22' Cruiser 260HP Alpha One

I just wanted to add that last fall when I first test drove the boat on 3 occasions I was able to get to 48mph (after new transom installed), but I can't remember what the max RPM was. Seems like it was higher than 4200 though. Last year I used an app on my phone for MPH. This year I have the Lowrance Elite 4 that I'm using, so maybe the phone app was off by a few MPH's.

 

[steelespike]

Re: Prop selection for 22' Cruiser 260HP Alpha One

With the 21" the calculator says with 4 adults slip is about 20% at both 3400 and 4200 using 44 and 36.
With 2 adults 4200/45 is about 19% 3400/38 is about 15%.
You may be able to improve on the slip with your props give them a try.
Many times as pitch goes down diameter goes up an inch is a lot but a 17" prop should act like a 17" prop.
You are dropping 4" The 17" may test like an 18" it may put you where you need to be.
Usually a heavy boat does better with a bigger diameter prop.I would try the 17" prop first.