Tugboat

Overview

A tugboat is a small, heavily built vessel whose entire design serves one purpose: to apply enormous pulling and pushing force to ships far larger than itself. Its value is not speed or cargo but bollard pull, the steady towline force it can develop, and the manoeuvrability to position a ship in a tight harbour. To deliver that, almost the whole hull is engine room and propulsion, wrapped in a rugged Steel Hull & Superstructure of welded steel with a heavy fendered bow for pushing.

Two independent drivelines drive the tug. Each Marine Diesel Engine diesel turns a Reduction Gearbox & Shaft whose propeller runs inside a Kort nozzle, a fixed duct that markedly increases thrust at the low speeds where a tug does its work. The boat is steered by Steering Gear gear behind the propellers and works ship lines through the Towing Gear aft. The crew controls everything from the Wheelhouse, and house power comes from the Diesel Generator and the Electrical System switchboard. The Fender Set protects both vessels during contact.

How it works

Each main engine burns diesel under turbocharged compression to spin its crankshaft, and a high-ratio reduction gearbox converts that into the slow, high-torque shaft rotation a large propeller needs. Inside its nozzle, the propeller accelerates a column of water astern; the reaction drives the tug, and the duct recovers thrust that an open propeller would waste, which is why a tug can pull so hard while barely moving. The flanking rudders deflect that race to swing the stern and let the tug pivot almost in place.

For towing, the powered Towing Gear winch renders line under load to cushion snatch loads, and a quick-release tow hook lets the crew drop the connection instantly if the tug is girted. The Wheelhouse gives all-round vision over radar and a chartplotter, while the diesel Diesel Generator and switchboard supply the winches, electronics and lighting independent of the main engines.