Formulas for: Speed, Slippage and RPM

M

MaPaHa

Petty Officer 1st Class
Joined
Jul 6, 2012
Messages
239
Here are some formulas for manually figuring theoretical speed, actual speed, slippage and RPM:

Theoretical Speed Equals:
RPM / Gear Box Ratio x pitch x .000947 = Theoretical Speed
5,000 rpm / 1.87 x 17 pitch x .000947 = 43 MPH Theoretical

Actual MPH Equals:
Theoretical MPH ? slippage % = Actual MPH
43 ? 10% = 38.7 MPH Actual

Grip vs Slippage Equals:
Theoretical MPH / Actual MPH = Grip
43 / 38.7 = 90% Grip vs. 10% Slippage

RPM Equals:
Actual MPH / Grip% / .000947 / Pitch = ?. Then ?. x Gear Box Ratio = RPM
38.7 MPH / 90% Grip / .000947 / 17 Pitch = 2671 x 1.87 = 4,995 RPM
 
S

steelespike

Supreme Mariner
Joined
Apr 26, 2002
Messages
19,069
Re: Formulas for: Speed, Slippage and RPM

Thanks for the information.
I have a prop calculator in my favorites.from Polson Enterprises.
I did a search for "prop calculator" this came up.Its a green page for easy identification.
Seems accurate determining any one of 5 variables.
 
Texasmark

Texasmark

Supreme Mariner
Joined
Dec 20, 2005
Messages
14,558
Re: Formulas for: Speed, Slippage and RPM

After the www. part add: go-fast.com works for me. So now you have two sources to solve your problem and I guarantee you, the answers are accurate. I can't give you the actual address as it has been edited.

Mark
 
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