#### captainlarry84

##### Rear Admiral

- Joined
- Sep 13, 2011

- Posts
- 1,295

- Likes
- 238

- Location
- Freeport NY

- Boat Make
- KristenFormer Charter Captain

__RPMs__divided by

__Reduction Gear Ratio__X=s

__Pitch__

X=s

__60__

__(minutes)__divided by

__12 (inches per foot)__divided by

__5280 (feet in a mile)__==s

__MPH__Divided by

__1.15__

__=__

__s Knots__

__Example my 31 JC 370 HP [email protected] 3300 RPMs 2:0 gear with a 23 X 21 propeller a WSOTY speed of 22.5 knots.__

__3300 (RPMs) divided by 2 = 1650 X's 21 (pitch) = 34650.00 X's 60 = 2079000.00 divided by 12 ("s per foot) = 173250.00 divided by 5280 (feet in a mile) = 32.81 (miles per hour) divided by 1.15 =__

__28.53 knots @ 100 % efficiency__

__22.5 knots (Boats actual speed divided by 28.53 knots ='s .79% efficiency__

__Therefore the only things you need to get your boats efficiency is the follow:__

__speed at wot @ RPMs__

__reduction gear__

__pitch of your propeller__