My 32 active thunder with 500 hps and msd boxes weight 7500 dry turns 5500 rpms at 84 mph on gps ,,, it used to run 87 so im thinking my slip is high. i would like to know the formula used to determin this.

Thanks RICK

http://www.go-fast.com/Prop_Slip_Calculator.htm

Keep in mind the lowest prop slip doesn't always equate to the fastest speed. You need to experiment to find what makes your boat happy.

I remember reading Joe's posts about prop testing on Audacity many years ago. He wasn't overly concerned with slip numbers compared to actual speeds, proper rpms and performance. He posted that he did a lot of prop testing/tweaking. Higher slip numbers actually strain the drives a little less.

Based off the calculator im runnig at 19 % what would be a good number maybe like 12-14 %.

Best i ever seen was 8% on a V hull. But i say 10 -14 % is ok.

I'm at 12-14% with stellings boxes on my 32.

10-14% is fine. We came up with a rule of thumb years ago at Mercury. under 20% for planing hulls. Under 15% for sport boats and under 10% for race applications.

rsstreiny, if your running 30 Bravo 1's the slip is only 17.43%. B1' are a little light on pitch and I'm guessing you have a 1.5:1 g.r.

Today everybody thinks a guy should run in the 10% or less range. That's just not true. And yes, sometimes slip can be your friend. Often we have propped boats for the best top number and had to run in the 15-20% range. Especially on V's. The reason is.....over trimming the drives to decrease the hull drag was the lesser of the 2 evils compared to the rise in slip number.

Brett

Thanks guys, im going to wait till i have my motors done in the spring and see where im at because im propably going to need 32 b1s with the add in power and then see what slip numbers im running.

What pitch props?