Towing Vessel License and TOAR

Domestic Towing Operations

Most domestic towing operators are exempt from STCW requirements. Vessels operating on inland waterways, rivers, and near-coastal routes under 200 nautical miles from a safe haven do not require STCW credentials for towing operations. The TOAR, USCG written examination, and base license requirements apply instead.

International Towing Voyages — 500 GRT and Above

Towing vessels of 500 GRT or more operating on international voyages must comply with STCW. Officers must hold STCW certificates of competency appropriate to their rank, complete Basic Safety Training (BST), and meet STCW watchkeeping standards. The TOAR remains a USCG domestic requirement and does not substitute for STCW certificates on vessels where STCW applies.

Exam Focus: What the Test Asks

The USCG exam typically tests STCW applicability with scenario questions: "A towing vessel of 600 GRT is making a passage from Miami to Nassau, Bahamas. Which certification is required?" The answer hinges on vessel size and whether the voyage is international. Know the 500 GRT threshold and the international voyage trigger.

Tow Astern

The most common ocean and coastal configuration. The tow rides behind on a hawser of controlled length. Best for rough water, long passages, and when the tow is a vessel capable of maintaining its own trim. The hawser length is adjusted so both vessels ride wave crests simultaneously, reducing surge loads.

Tow Alongside

The tow is made fast alongside the towing vessel with bow and stern lines, breast lines, and spring lines. Used in protected waters, harbors, and for final docking maneuvers. The combined vessels are maneuvered as a unit. Steering is influenced by the position of the tow relative to the towing vessel.

Push Ahead (Pushing)

The towing vessel pushes the tow from astern, typically used on inland waterways and rivers. Barges are pushed in flotillas using knee lines and face wires. The tug is notched into or faces up to the barge stern. This method is standard practice on the Mississippi River and Western Rivers system.

Catenary — The Key Shock Absorber

Catenary is the natural downward curve or sag in a suspended hawser caused by its own weight and the angle of tow. A hawser hanging in a deep catenary acts like a spring — as the towing vessel and tow encounter different wave periods, the catenary flattens and steepens rather than transmitting the full surge load as a shock.

In heavy weather, operators add a chaser — a heavy weight (often a length of chain or a steel ball) — to the middle of the hawser. The chaser slides down to the low point of the catenary and adds mass, deepening the sag and increasing the hawser's spring effect dramatically.

Surge Loads and Snatch Loads

A surge load occurs when the tow and towing vessel pitch or surge to opposite extremes simultaneously, momentarily taking all catenary out of the hawser. The resulting snatch load can be several times the static tension and can exceed the hawser's safe working load. Hawser parting almost always occurs at maximum surge load, not during steady towing.

Towing Bitts and Cleats

Towing bitts are the primary securing point for the tow hawser on the towing vessel. They consist of two vertical posts mounted to a strong structural base. The hawser is belayed or secured around the bitts using figure-eight turns. Bitts have a rated safe working load that must not be exceeded.

Trip Lines and Pelican Hooks

A pelican hook is a quick-release fitting used to secure the tow hawser or bridle. It consists of a pivoting bill locked by a ring or toggle. To release, the ring is lifted (or a trip line is pulled) and the bill swings open, releasing the hawser instantly. This is the primary emergency release mechanism for towing operations.

Rule 36 — Signals to Attract Attention

Rule 36 permits any vessel to use any light or sound signal to attract the attention of another vessel, provided the signal cannot be mistaken for an authorized signal. A towing vessel maneuvering in a confined harbor may use a searchlight or additional lights to draw attention to a difficult tow operation. The rule applies in all waters and is not restricted to any specific situation.

Restricted Visibility with a Tow — Rule 35

In restricted visibility, a towing vessel making way sounds one prolonged blast followed by two short blasts at intervals of not more than two minutes. A vessel being towed (if manned) sounds one prolonged blast followed by three short blasts, immediately following the signal from the towing vessel.

How Squat Develops

As a vessel moves through water, the hull displaces water and creates a low-pressure zone beneath and around the hull. In deep open water, this zone dissipates quickly. In shallow water, the seabed constrains water flow, increasing velocity and reducing pressure. The hull sinks bodily into the low-pressure zone — this sinkage is squat. The vessel also trims by the stern because the pressure reduction is greatest aft, beneath the propeller.

Squat Implications for Towing

Changed Performance Parameters

Tow Sheering and Yawing

A tow astern can develop a rhythmic sheering or yawing motion where it swings from side to side behind the towing vessel. This is caused by the tow developing a slight drag asymmetry — one side has more water resistance than the other — which begins a pendulum-like oscillation. Sheering can be severe enough to capsize a light-draft tow in rough conditions.

Tow Overriding — When the Tow Catches Up

If the towing vessel is forced to slow suddenly (grounding, engine failure, traffic), the tow's momentum carries it forward. If the tow catches up and overtakes the tug, the hawser can go slack and then suddenly come taut with an enormous snatch load as the tow passes and the line comes up short. Worse, the tow can override and collide with the tug. When forced to stop suddenly with a tow astern, the correct action is to warn the tow vessel crew and attempt to swing the stern to one side to avoid the overriding tow.

Parted Hawser

1. 1.Immediately call all hands clear of the towing deck snap-back zone
2. 2.Sound the danger signal and notify the tow by radio
3. 3.Maneuver to stay clear of the now-drifting tow
4. 4.Recover the parted hawser end before approaching the tow again
5. 5.Assess hawser damage — determine if it can be re-spliced or must be replaced
6. 6.Re-approach the tow from the leeward side and re-establish tow
7. 7.Document time, location, and conditions of hawser failure

Man Overboard While Towing

1. 1.Throw lifebuoy immediately and call MOB on VHF if not previously broadcast
2. 2.Designate a lookout to maintain visual on the person in the water
3. 3.Do NOT attempt a sharp turn with a tow astern — risk of overriding the tow
4. 4.Slow down gradually to begin a broad recovery arc
5. 5.Notify the tow vessel crew of the situation
6. 6.Consider releasing the tow only if the MOB recovery is otherwise impossible
7. 7.Use the Williamson Turn modified for the tow configuration

Taking a Vessel in Tow That Is on Fire

1. 1.Stay clear until the fire is extinguished or controlled
2. 2.Approach from upwind and upcurrent
3. 3.Do not connect a hawser to a vessel with active flames on the towing deck
4. 4.Use a long hawser to maintain maximum separation
5. 5.Notify the Coast Guard with position, vessel description, and number of persons aboard
6. 6.Tow toward nearest safe haven — do not cross open water with an uncontrolled fire
7. 7.Keep fire extinguishing equipment ready on the towing vessel

Tow Taking on Water

1. 1.Radio the tow crew for status — flooding rate and pump capacity
2. 2.Assess whether the tow can remain afloat for the passage to port
3. 3.If flooding is controllable, proceed to nearest safe haven at best speed
4. 4.If flooding is uncontrollable, prepare to evacuate tow crew
5. 5.Notify Coast Guard immediately with position and number of persons
6. 6.Move to alongside towing to facilitate crew transfer if needed
7. 7.Abandon tow only after all persons are safely off the vessel