Why does prop spin when in neutral?

RTripp

Petty Officer 2nd Class
Joined
Feb 23, 2018
Messages
114
It doesn't spin fast and I can stop it with my foot. But, I did notice yesterday in a very calm spot the spin was enough to push the boat at a very slow crawl.
 

Scott Danforth

Grumpy Vintage Moderator still playing with boats
Staff member
Joined
Jul 23, 2011
Messages
50,675
gear oil drag. prop exhaust will also push the boat
 

Joe Reeves

Supreme Mariner
Joined
Feb 24, 2002
Messages
13,262
Deleted error... my mind was elsewhere apparently. Yes F_R, I'm aware of the lower unit setup... was out to lunch so to speak!
 
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F_R

Supreme Mariner
Joined
Jul 7, 2006
Messages
28,226
I know that Joe knows this, but in reality the pinion gear AND both directional gears are all spinning any time it is running. But the reverse gear is provided with better bearings (less drag) because it usually is spinning in the opposite direction of the prop shaft. Therefor the gear with the most bearing drag (forward) wins out in the equality test and the prop turns in that direction.

Please don't stick your foot in it any more.
 

racerone

Supreme Mariner
Joined
Dec 28, 2013
Messages
38,728
The pinion turns both forward and reverse gears when the engine is running.-----On most motors the forward gear has a plain bushing on the propshaft.----The reverse has a needle bearing that often is NOT contacting the propshaft.----It is drag in the forward bushing that turns the propshaft.---On most motors the gears are not connected to the propshaft by splines .---It is the clutch dog that is splined to the propshaft.
 
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Crosbyman

Vice Admiral
Joined
Nov 5, 2006
Messages
5,771
some of you less younger fellows may remember the old VW commercial/demo explaining modern "automatic transmissions" where the demo guy would use a large bowl on a lazy Suzan plate , an electric egg beater and olive oil....

without touching the bowl.... the egg beater would spin the oil in the bowl....and magic:confused: the bowl itself would start turning thanks to the friction... with the olive oil.

same with props I guess
 
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