River Pusher Tug

Overview

A river pusher tug, called a towboat on many waterways despite the name, is a powerful, shallow-draft vessel built to push a tow of barges rather than pull it. Its bow is flat and square so it can press against the square stern of a barge string and drive the whole assembly forward as one rigid unit. The vessel concentrates a large amount of engine power in a small, maneuverable hull, with a tall wheelhouse that lets the pilot see over a tow that may stretch hundreds of meters ahead. The main building blocks are the Hull Structure, the twin Propulsion Train trains, the Steering System system, the Deckhouse & Wheelhouse, and the Barge Coupling Gear that locks tug and barges together.

Supporting these are the Electrical System system, the Auxiliary Systems that handle fuel, cooling and bilge water, and the Deck Outfit of capstans, bitts and fenders. Everything is sized around one job: producing high thrust at low speed and steering a long, heavy tow through the bends and locks of a river.

Hull and push bow

The Hull Structure is a flat-bottomed steel box with a shallow draft so it can work rivers that would ground a deeper vessel. Its defining feature is the Push Bow (Tow Knees), a flat vertical structure with tow knees that bears directly on the barge stern and transmits pushing thrust without a towline. Aft, Skeg fins ahead of the propellers improve straight-line tracking and shield the screws from debris and grounding.

Internally the hull is divided by Watertight Bulkhead walls into watertight compartments and stiffened by Transverse Frame members. The shape is a compromise: blunt and beamy enough to push squarely against a barge, yet still able to slip astern and turn quickly, which is why these boats look stubby compared with seagoing tugs.

Propulsion

Each Propulsion Train train starts with a Main Diesel Engine, a medium-speed marine diesel built around an Engine Block, a Crankshaft and several Piston & Conrod units, breathing through a Turbocharger and fed by a Fuel Injection System system. The engine drives a Marine Reduction Gearbox with a Reversing Clutch that selects ahead or astern without stopping the engine, then power passes down a Propeller Shaft through a sealed Stern Tube & Seal to the Propeller.

The propeller runs inside a Kort Nozzle, a shrouding duct that markedly increases thrust at the low speeds at which a tug pushes a heavy tow. That bollard pull, the static pushing force, matters far more here than top speed, so the whole train is geared and ducted for it. Two such trains side by side give the redundancy and turning authority a single screw could not.

Steering and wheelhouse

Maneuvering a long tow demands more rudder authority than an ordinary vessel needs. The Steering System system uses several rudders: a main Rudder behind each propeller for ahead steering, plus flanking rudders forward of them that steer while backing down, all driven through Rudder Stock stocks by a hydraulic Hydraulic Steering Gear. This lets a pilot pivot the tow, hold it against a current, and ease it into a lock.

The Deckhouse & Wheelhouse carries the crew accommodation below and an elevated Elevated Wheelhouse, sometimes telescoping, so the pilot can see over the barges. The Helm Console gathers the throttle controls, steering lever and instrument displays, and a Navigation Suite of radar, GPS compass, electronic charts, VHF radios and searchlights supports night and low-visibility running on busy rivers.

Coupling gear

What turns a tug and a string of barges into a single controllable vessel is the Barge Coupling Gear. Padded Push Knee surfaces on the bow press against the barge, and heavy Face Wire wires are run from the tug to the barge and hauled bar-tight by Coupling Winch winches and hand Wire Ratchet ratchets against Timberhead Bitt bitts. Tensioned correctly, the coupling is rigid enough that the tow steers as one hull, with no slack to let the barges wander.

Power, auxiliaries and outfit

The Electrical System system runs on two diesel Diesel Generator Set units feeding a main Main Switchboard, with batteries and a Shore Power Connection for power in port. The Auxiliary Systems keep the propulsion plant alive: a Fuel Storage & Transfer storing and transferring diesel, a Bilge System with an Oily Water Separator to discharge bilge water cleanly, Sea Chest & Strainer intakes drawing river water for cooling, a starting-air compressor and a fire pump. On deck the Deck Outfit adds capstans for handling wires, mooring bitts, a row of fenders and life rafts.

Use and operation

In service a pusher tug rarely stops. It makes up a tow at a fleeting area, couples on, and pushes it for days at a stretch, the crew standing watches around the clock. River work means constant adjustment: setting up for bends, holding station in current while waiting for a lock, and breaking the tow into sections to lock through where the chamber is too short for the whole assembly. The design is specialized for exactly this, high thrust at low speed and tight maneuvering, rather than the open-water seakeeping a harbor or ocean tug needs. That specialization is why a single pusher tug can move a tonnage that would take a long train of trucks, at a fraction of the fuel per ton-mile.