A twin-screw steamer (or steamship) (TSS) is a steam-powered vessel propelled by two screw propellers, one on either side of the plane of the keel.
References
Twin-screw steamer Wikipedia(Text) CC BY-SA
A twin-screw steamer (or steamship) (TSS) is a steam-powered vessel propelled by two screw propellers, one on either side of the plane of the keel.