Astern propulsion (as applied to a ship) is a maneuver in which a ship's propelling mechanism is used to develop thrust in a retrograde direction. ... In a ship with a gas turbine engine and a variable-pitch propeller, astern thrust is simply a matter of changing the propeller pitch to a negative value.

How does a ship move astern?

When a propeller is rotating, it produces thrust on water. Now the thrust from propeller is transferred to the water. Since the amount of water is enormous according to Newtons Third Law, the thrust comes back to the ship and this thrust moves the ship in ahead (or astern) direction.

What is astern turbine?

The astern turbine is a single axial flow, velocity compounded, condensing impulse turbine consisting of one or two Curtis stages located on the forward and/or after end of the LP turbine.