Ducted propeller for submarine - with duct streamlined for thrust but with drag when propeller is stationary

摘要

The submarine is fitted with a single ducted propeller in the tail, with the duct conical with a wider front area. This concentrates the flow over the propeller and provides improved thrust control. The pitch of the cone, and the profile of the duct are chosen so that streamline flow results when the propeller is operating, but with drag when the propeller is stationary. - The propeller pulls water into the duct and alters the flow pattern around the leading edge of the duct. When the propeller is stopped the inlet water flow sets up eddy currents about the leading edge and results in a braking effect.