Harbour tug

A harbour tug is a powerful, highly maneuverable vessel used to assist ships berthing, unberthing, and turning within a port. Modern harbor tugs are azimuth-stern-drive (ASD) or tractor (Voith Schneider or forward azimuth) designs whose thrusters give full thrust in any direction, unlike the older conventional single-screw tug. They are rated by bollard pull, the static pull at the line, typically 30 to 90 tonnes for ship-handling work, sized to the largest ship and the worst wind and current at the berth. Tugs push or pull on a made-fast line, or work as an escort tug rendering steering and braking force to a laden tanker in a confined approach. Their number per ship is set by the port’s towage rules.