Alternative propulsion

I am building a self propeld barge and i intend to use a four stroke six cylinder gasoline car engine. It would be coupled with an automatic transmission system and the drive shaft would be coupled to the propeler. Can any one tell me the ideal effcient rpm of the propeller so i can calculate my gear ratio. Thanks.

Wemdoug

 

Depends on the power to displacement ratio, the prismatic coeficient, the prop diameter, the prop pitch, the expected speed, and several other things. Also, you will need a double thrust bearing

 

It would be coupled with an automatic transmission system and the drive shaft would be coupled to the propeler.

The prop size will need figguring but the auto tranny will solve the What Gear? problem.