Does any one know how to calculate the speed of a prop? I use to know the math but I forgot it. It was something like rpm x pitch divided by gear ratio . If any one knows could you please post it. I am trying to figure out my slip factor in a 1999 28 Eliminator Daytona twin HP 500's bravo ones with 1:36 gears & 30 pitch Bravo 1 four blades turning 5050 rpms.I think I should be turning 5300 and maybe 30's are too much prop. Wondering if I should go down to 28's or have these brand new 30's worked on by Huston Prop. I here Darren is a wizard.

Here is one. Search Yahoo for prop slip calculator and take a pick.

http://www.rbbi.com/folders/prop/propcalc.htm

Try BAM's website,they are a sponsor here and have some good slip and speed calc's with diff hull types/wieghts

Question, what percent of prop slippage is about average ? I just did the math on that site, and I'm getting just over 23% slip. Never checked it before,and now with a fresh motor, wondering if I am missing some mph., and looks like I sure could be. Running a 23 pitch mirage now. Boat is a 23 foot powerplay, v hull, and I guess I will try a 24p or maybe another make ..??

easier thru "go-fast.com",,,then "knowledge base"?

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

use this

Thanks for the info guys. I just calculated my speed and apparently the slip on my boat is about 9% 5050 rpm x30P=151,500 / 1436.16=105 x .91= 95.5 & I am getting 95 on GPS. I think 9% slip is probably correct for a 28 eliminator daytona cat with twin hp500's.Do you guys think I should go down to 28p & get the rpm's up to 5300 and maybe less slip like 7% that math would be 5300 x 28p=148,400 / 1436.16=103.33 x .93= 96 but only 1 mph does not really mean much or do you think having Huston Propellers do there magic on the brand new bravo1 30's I just bought. Any help is greatly appreciated