Twin-Screw Tug

A conventional tug driven by two fixed propellers, usually in nozzles, with rudders aft, as distinct from azimuth (ASD) or tractor tugs. Twin screws give better maneuverability and redundancy than a single-screw tug and let the hull develop solid astern thrust, but the tug cannot vector thrust sideways, so it works mainly in direct push-pull towing rather than the high indirect modes of escort tugs. The arrangement remains common on river, pusher, and budget harbor tugs where simplicity and bollard pull per dollar outweigh omnidirectional control.