Towing & Ship-Assist

Towing astern — masthead lights:

A power-driven vessel towing astern shows two masthead lights in a vertical line when the tow (measured from the stern of the towing vessel to the after end of the tow) is 200 meters or less. When the length of the tow exceeds 200 meters, she shows THREE masthead lights in a vertical line. This is the single most-tested towing-light fact.

Towing astern — other lights:

In addition to the masthead lights, the towing vessel shows sidelights, a sternlight, and a yellow towing light in a vertical line above the sternlight. The yellow towing light is shown only when towing astern.

Vessel being towed:

The towed vessel (or object) shows sidelights and a sternlight. It does NOT show a yellow towing light and does NOT show masthead lights.

Day shape — long tow:

When the length of the tow exceeds 200 meters, both the towing vessel and the towed vessel/object display a diamond shape where it can best be seen, by day.

Pushing ahead / towing alongside:

A vessel pushing ahead or towing alongside (not a composite unit) shows two masthead lights in a vertical line, sidelights, and a sternlight — but NO yellow towing light. When a pushing vessel and the vessel pushed ahead are rigidly connected as a composite unit, they are lit as a single power-driven vessel.

Inland difference:

Under Inland Rules, a vessel pushing ahead or towing alongside displays two yellow towing lights in a vertical line at the stern (instead of a sternlight). This is a key COLREGS-vs-Inland distinction tested frequently.

Towing vessel (underway, making way or stopped):

A vessel towing or pushing sounds, at intervals of not more than 2 minutes, one prolonged blast followed by two short blasts (— • •). This is the same signal as a vessel not under command, restricted in ability to maneuver, constrained by draft, sailing, or fishing — the "one prolonged plus two short" group.

Manned towed vessel:

A vessel being towed (or the last vessel of the tow if more than one is towed), if manned, sounds at intervals of not more than 2 minutes one prolonged followed by three short blasts (— • • •). Where practicable this signal is made immediately after the signal of the towing vessel.

Why it matters:

The towed-vessel signal (prolonged + three short) is unique in the Rules and identifies the dangerous trailing end of a tow in fog — the part another vessel is most likely to run into because the tow wire is unlit and the barge may be a long way behind the tug.

Towing on a hawser (astern):

Used in open water and offshore. The towline (synthetic hawser or wire) connects to the barge through a bridle — two legs meeting at a fishplate or delta plate so the strain is shared and the barge tracks straight. The catenary (the sag in the towline) acts as a shock absorber, smoothing surge loads; in heavy weather you pay out more wire to increase the catenary. Match towline length to sea state and keep tug and tow "in step" with the swell so both rise and fall together rather than coming taut on opposite faces of a wave.

Towing alongside (on the hip):

The tug is made fast to the side of the barge with a head line, stern line, spring line, and breast line. Used in confined waters and for docking because the tug can control the unit precisely and back down. The tug is typically positioned aft on the barge so its propeller and rudder have authority.

Pushing ahead:

The tug is made up in notches or against the stern of the barge with face wires and push gear. Most efficient and maneuverable in protected water (rivers, ICW); a rigidly connected push unit handles like one vessel. Not used in open seaway unless the unit is designed for it (ATB).

Gob wire / gog rope (the tow strap):

A gob (or "gog") wire is a controllable strap led from the tug's after deck that holds the towline down and close to the centerline, limiting how far the towline can swing to the side. It is the primary defense against girting: by keeping the towline aft and low, it preserves the tug's ability to maneuver and reduces the capsizing lever arm.

Norman pin / tow pins and the towing winch:

Tow pins (Norman pins) on the after deck corral the towline and keep it from sweeping the deck. The towing winch pays out and recovers wire under power and usually has a brake and, on modern tugs, a render/recover function and an emergency quick-release.

Two compliance options:

An owner/operator chooses how to demonstrate compliance: - The Coast Guard inspection option (annual USCG inspections), or - The Towing Safety Management System (TSMS) option, using an approved third-party organization (TPO) to audit and survey.

Towing Safety Management System (TSMS):

A documented safety-management system covering policies, procedures, drills, maintenance, and corrective action — conceptually similar to the ISM Code. Under the TSMS option, a TPO conducts external audits of the company and surveys of the vessels.

Certificate of Inspection (COI):

States the vessel's route, manning, equipment, and conditions of operation. It must be maintained valid; Subchapter M brought most towing vessels under the COI requirement for the first time.

Towing vessel record (TVR):

The vessel keeps a Towing Vessel Record documenting tests, inspections, maintenance, and drills — the onboard evidence the management system is actually being followed.

Health, safety, and watchkeeping:

Subchapter M reinforces work-hour limits, drills, and the requirement that the vessel be properly manned per its COI. Master/mate of towing and the towing officer assessment (below) tie the credential to demonstrated competence.

What the TOAR is:

A record in which a Designated Examiner (DE) observes and signs off that the candidate has demonstrated each required practical skill — making up tows, handling on a hawser, alongside, and pushing, maneuvering, emergency response, and applicable navigation skills for the route (inland, Western Rivers, or near-coastal/oceans).

Designated Examiner (DE):

An experienced, qualified individual (approved through a TSMS or the Coast Guard) who is authorized to evaluate and sign the TOAR. The DE attests to real, observed performance.

Route-specific:

TOAR skill sets differ by the waters endorsed — Western Rivers towing, inland/limited, and near-coastal/oceans each have their own required competencies, reflecting the very different boat-handling demands of river current versus open-water hawser towing.

Relationship to the credential:

A mariner pursuing a Master or Mate (Pilot) of Towing Vessels endorsement combines sea service, the Coast Guard exam, and a completed TOAR. The TOAR is the hands-on gate.

Conventional tug:

Single or twin screw with a rudder, and often a towing winch forward (for ship work) or aft. Limited in pushing/pulling angles compared with omnidirectional tugs.

Tractor tug:

Propulsion units (Voith Schneider cycloidal, or azimuthing units) located forward, under the hull, with the towing point aft. Highly maneuverable and able to apply thrust in any direction without first swinging the stern.

ASD (azimuth stern drive) tug:

Two azimuthing (Z-drive) thrusters at the stern that rotate 360°, with the towing staple/winch usually forward. The workhorse of modern ship assist — it can pull, push, and steer in any direction and transition quickly between modes.

Direct vs. indirect mode (escort):

- Direct mode: the tug applies thrust straight along the towline by its own propulsion — limited to roughly the tug's bollard pull. - Indirect mode: at speed, the escort tug presents its hull at an angle to the water flow so hydrodynamic lift and drag on the hull generate steering and braking force on the ship — forces that can far exceed the tug's bollard pull. Indirect mode is the reason a relatively small escort tug can steer or stop a large tanker in an emergency.

Bollard pull:

The static pulling force a tug can exert, measured at zero speed (in tonnes or pounds). It is the standard rating of a tug's power for assist work, but remember indirect escort forces can exceed bollard pull at speed.

Communication and the conning officer:

The pilot or master conning the ship directs the tug(s) by standard commands and whistle/radio signals. Clear, unambiguous orders and read-backs are essential — a misheard "push" for "back" can damage the ship or capsize the tug.

What girting is:

Girting occurs when the towline comes abeam (athwartships) and the pull of the line, combined with the tug's forward motion or the assisted ship's motion through the water, heels the tug over. If the towline cannot be released or repositioned, the tug is rolled over and downflooded — capsize can happen in seconds. It most often happens to ship-assist tugs made fast to a moving ship, and to towing tugs whose tow takes charge in current or wind.

Preventing girting:

- Keep the towline as far aft and as low as possible — the gob/gog wire is the primary tool, limiting the athwartships angle of the line. - Keep the tug's stern free to swing so the tug can "follow" the line rather than being held beam-on. - Match speed to the assisted ship; never let the ship's speed build to where the tug cannot keep its line astern. - Maintain situational awareness of the line's angle at all times.

Quick release:

Ship-assist and towing winches/hooks are fitted with an emergency quick-release (a release that can be operated from the wheelhouse and locally) so the towline load can be dumped instantly if girting begins. Crews drill the quick release; a release that jams is what turns a girting into a capsize.

Tow takes charge / parted towline:

If a tow overruns the tug in a following sea or current ("the tow takes charge"), or if a towline parts, the immediate concerns are recovering control without girting, the danger of a parted wire snapping back (stand clear of the bight and the recoil zone), and re-establishing the tow or anchoring the barge before it grounds or fouls traffic.

Man overboard and deck safety:

Tow decks are among the most dangerous workplaces afloat — bights of wire under load, snap-back zones, and heavy gear. Never stand in the bight of a line, keep clear of the towline's sweep, and treat every wire under strain as lethal.

ATB (articulated tug-barge):

The tug sits in a notch in the barge's stern and is connected by a mechanical coupling system (pins into the barge's ladder racks) that allows the tug to pitch independently (articulate) while moving with the barge in yaw and surge. The connection lets the unit work in open seaway far better than a pushing tug, while still allowing the tug to disconnect.

ITB (integrated tug-barge):

A more rigid connection in which the tug and barge function essentially as one vessel; less articulation than an ATB. Historically some ITBs were crewed and inspected as a single unit.

Lights:

A composite unit (rigidly connected tug and barge) is lit and treated as a single power-driven vessel under Rule 24, not as a towing operation — an important distinction from a tug pushing a separate barge.

Why ATBs dominate coastwise petroleum:

The articulated coupling gives near-pushing efficiency and maneuverability with seakeeping good enough for coastal voyages, at lower crewing cost than a self-propelled tanker — which is why so much U.S. coastwise petroleum moves on ATBs.