Prop pitch recommendation

[Gary H NC]

Finally got a GPS and was testing speed at WOT.
175 HP Johnson Cross Flow
42 MPH at 5000 RPM WOT
19 pitch 3 blade Stiletto II
21 ft boat with 60 gallons of fuel and 3 people on board.
How bad is the slip of this setup?

Wondering if i should try a 17 pitch..

 

[steelespike]

Re: Prop pitch recommendation

Can't really address slip but it appears your right on.
If you feel your setup (vertical height and trim) is ideal and that is your typical load a 17" pitch seems to be in order.would put you at about 5,400

 

[Gary H NC]

Re: Prop pitch recommendation

I have played with the engine height and got it as high as i can without prop blow out.I can trim full out and just barely lose bite.
I think i may buy a 17 pitch aluminum just to try.
I have 2 SS 19 pitch props.Too bad i can't find someone to do a trade..

If i prop to a 17 will i give up any top speed? I know it should get my RPMs up to a better WOT range.

 

[codertimt]

Re: Prop pitch recommendation

If the rpm is accurate and I found the correct gear ratio for your motor (1.86?), then the calculator I use puts slip at around 13%.

As stated above, a 17 will put your rpms up to around 5400 and if everything else stays the same that means(according to the calculator) you will lose about 2mph at WOT.

However, I believe the WOT rpm range for this motor is listed at between 4500-5500. So you're well within that range right now. If you could get ahold of a 17, you might play with it. Your holeshot should improve and you might find it puts you motor in a better rpm range for fuel economy while at cruising speed...or it might not.

 

[steelespike]

Re: Prop pitch recommendation

I have played with the engine height and got it as high as i can without prop blow out.I can trim full out and just barely lose bite.
I think i may buy a 17 pitch aluminum just to try.
I have 2 SS 19 pitch props.Too bad i can't find someone to do a trade..

If i prop to a 17 will i give up any top speed? I know it should get my RPMs up to a better WOT range.

If you change from stainless to aluminum there is more at work than a simple pitch change.The stainless is generally more efficient so you could lose more speed with aluminum.Some dealers will let you try props if you intend to buy.
A prop shop may be able to repitch one of the 19s.

 

[Gary H NC]

Re: Prop pitch recommendation

If you change from stainless to aluminum there is more at work than a simple pitch change.The stainless is generally more efficient so you could lose more speed with aluminum.Some dealers will let you try props if you intend to buy.
A prop shop may be able to repitch one of the 19s.

Thats a good point on the aluminum. I think i'll check around and find a 17 SS to test.
I know a guy who may be willing to trade one..