what does a reduction unit do on a air boat

[josh_2562]

why do people use them what do they help with. thanks for the help

 

[jpatter123]

a prop is only designed to turn a certain RPM. Lets use 2800 as a ceiling for a prop's rotation. So you have a car motor that can turn 6000 but doesn't start making real horespower tell 4500 but you can only turn the prop at 2800. You use a gear reduction so the engine is turning 4500 but lets say using a 2:1 gear reduction the prop is only turning 2250. It also increases the torque at the output end allowing you to swing a bigger propeller.

 

[josh_2562]

ok i under stand now thanks for to help