prop slip ?

[77charger]

Can somone figure this out for me
21 ft elim open bow
4850rpm 59mph(gps)max(good condtions) avgs 57@4800 mostly
aplha drive 1.50 gear
21 pitch 3 blade stnls

[Beautiful Noise]

Hmmmmmmmmmm Faster than me Sorry I can't Help.Don't mind me I'm just trying to Build up my Post Count
Steve

[Toffen]

Hi!
4850rpm 59mph(gps)max(good condtions) avgs 57@4800 mostly
aplha drive 1.50 gear
21 pitch 3 blade stnls
4850 x 21 / 1056 / 1.5 = teoretical speed = 64,3 mph. Slip approx. 9% which is very very good.
Cheers, Toffen G

[77charger]

thanks toffen.What is the range considered good Ex 0-12%

[Havasu Hangin']

10% is good for a V-hull...cats can be a little better...

[TCHB]

After running a prop slip calculation with your set up you are right on target. If you pitch it up you will drop the rpm down and loose MPH. Tested a 19 ft boat with a very flat v bottom with a 350 merc cruiser, alph 1 drive, 21Px13 3/4 prop. It ran at 4800 rpm @ 60.1 MPH. The boat weight was 2400#.

[HavasuBarney]

This will work to figure any of the variables.
http://www.boatpropellers.com/propcalc.html

[Trash]

I came up with the same slip%. Setup looks pretty good. Cats with higher x-dimensions tend to have the slip numbers improve at higher speeds. If running a labbed prop in the midrange the slip will be worse. The ***boat article with the twin engine eliminator cats with varying setup, standoff and props showed that very well.