too much slip at WOT only

krisnowicki

Lieutenant Junior Grade
Joined
Jul 11, 2007
Messages
1,172
I have a Johnson 225. Gear ratio is 1.86

I just painted and tuned her up. ( the bottom is not painted) boat floats straight and engine runs great.

@ 3000 -3100 I am getting 30-31 mph but, I am getting 26-27% slip at 5500 WOT I am only getting 41 mph.

All speeds are gps. What would cause a prop to slip only at high rpms?

Pic is of the boat
 

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steelespike

Supreme Mariner
Joined
Apr 26, 2002
Messages
19,069
Re: too much slip at WOT only

It would help to know what boat; brand,dry weight,style,Deep V,What brand,size,model prop? Is the bottom clean and smooth.
Slip figures are only as accurate as their input.Excessive application of trim tabs may cause higher slip numbers.Heavy boats tend to have higher slip numbers.
Imperfections in the prop,boat bottom or devices that might disturb the water near the prop might increase slip a poorly modified prop or a style not appropriate to the application.
 

krisnowicki

Lieutenant Junior Grade
Joined
Jul 11, 2007
Messages
1,172
Re: too much slip at WOT only

hull is a 89 answer police boat. meduim V weighs about 4000 when all fished out. The bottom is smooth fiberglass no paint. No trim tabs and the prop is a 21p ballistic.
 
Joined
Jun 4, 2009
Messages
1
Re: too much slip at WOT only

The problem is the ballistic prop, I tried one on my 21B mako and was getting 21% slip at wot, I just installed a mercury mirage plus and I'm now down to 6% slip at wot.
 
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