Speed Calculator & Slipage

[Brazos River Rat]

Can some one tell me where to find the formula for speed and slipage.
TR4 RPM 5500 11-16 prop 22% gears. Might have 25% gears ...
What speed is this.

[Snowboat]

RPM X pitch X gear X slip X .0009469 = speed
7000 X 15 pitch prop X .80 (20 % slippage) X 1.18 (18's in the box) X .0009469 (a constant).
Verify the slippage with GPS.

[Brazos River Rat]

Thanks;
The Box is comming apart soon by J.J and then I will see what gears it has in it. Then I can calculate more accurately..
20% slippage is common ???...
I have to buy a new GPS , my old one died...