A twin-screw steamer (or steamship) (TSS) is a steam-powered vessel propelled by two

screw A screw is an externally helical threaded fastener capable of being tightened or released by a twisting force (torque) to the screw head, head. The most common uses of screws are to hold objects together and there are many forms for a variety ...

propellers, one on either side of the plane of the

keel The keel is the bottom-most longitudinal structural element of a watercraft, important for stability. On some sailboats, it may have a fluid dynamics, hydrodynamic and counterbalancing purpose as well. The keel laying, laying of the keel is often ...

Arrangement

All propellers produce a transverse thrust, also called screwing effect or starting bias, which gives a tendency for end of ship to move sideways. In a twin-screw ships the port propeller is usually left-handed and the starboard right-handed, to cancel out the transverse thrust and avoid propeller walk.

References

Steamboats Ship types {{ship-type-stub