1.14 Lights & Shapes for Towing and Pushing (Rule 24)

Rule 24: Lights and Shapes for Towing and Pushing

Tugs and their tows are among the most dangerous vessels a six-pack operator meets: the tow may be a barge riding low and dark, connected by a hawser you cannot see, and the whole assembly cannot maneuver quickly. Rule 24 tells you how to read a tug at night and by day so you never steer between a tug and her tow. The load-bearing number in this rule is 200 metres of tow length.

The towing vessel (towing astern)

A power-driven vessel towing astern shows her normal Rule 23 lights plus:

• Masthead lights in a vertical line — two if the tow (measured from the tug's stern to the after end of the tow) is 200 m or less, or three if the tow exceeds 200 m.
• Sidelights and a sternlight as usual.
• A towing light — a yellow light with the same 135° arc as a sternlight — mounted above the sternlight.
• By day, if the tow exceeds 200 m, a diamond shape where it can best be seen.

So at night the tell for a tug towing astern is the yellow towing light stacked above the white sternlight, combined with an extra masthead light. Count the masthead lights to gauge the tow: two vertical masthead lights = tow of 200 m or less; three = a very long tow (over 200 m).

The vessel or object being towed

The towed vessel (the barge astern) shows:

• Sidelights, a sternlight (but no masthead light and no yellow towing light), and
• By day, a diamond shape at or near the after end. If the tow exceeds 200 m, an additional diamond as far forward as practicable.

If a towed object is 100 m or more long, it also carries additional all-round white lights spaced so no gap exceeds 100 m — a detail more relevant to large ocean tows than to six-pack waters, but testable.

Pushing ahead and towing alongside

When a tug is pushing ahead or towing alongside (not astern), the geometry is different and the lights change — and this is where International and Inland Rules split, a classic exam trap:

Under Inland Rules a vessel pushing ahead or towing alongside shows two yellow towing lights in a vertical line at the stern (in place of the sternlight); under International Rules she simply shows an ordinary sternlight. On U.S. Inland waters, barges being pushed ahead also carry a special flashing yellow light at the forward end and sidelights — a signature of the push-boats you will see on rivers and in harbors.

Inconspicuous or partly submerged tows

Rule 24 also covers inconspicuous, partly submerged vessels or objects being towed — a swamped barge, a section of dock, a half-sunk hull. Because these ride low and are nearly invisible, they carry extra all-round white lights: one at or near each end (with the forward end exempt when it is a "dracone," a flexible fuel barge), and, if the object is 25 metres or more in breadth, an additional all-round white light at each side. If the object is 100 metres or more long, additional all-round white lights are spaced so no gap exceeds 100 metres, and a diamond marks the after end. The takeaway for a small-boat operator: a scatter of low white lights strung out on the water behind a tug, with no obvious hull, is very likely a hazardous submerged tow — treat the whole strand as a solid obstruction.

Why you must never cut between tug and tow

If you see a tug displaying a towing light and cannot see the tow, assume there is a long, low, unlit-looking barge somewhere astern of her, connected by a hawser or a bridle that rides just under the surface. Steering between the two can part your propeller on the tow wire or put you under the bow of a barge that cannot stop. Always pass astern of the entire assembly — pick a point well behind the last diamond shape or the barge's sternlight.

Worked example

At night, ahead of you, you see a vessel showing three white masthead lights in a vertical line, a yellow light above a white light at her stern, and both sidelights, and — farther back and off to one side — a dim sternlight with no masthead light. Diagnose it: the three vertical masthead lights plus the yellow-over-white at the stern mark a tug towing astern with a tow that exceeds 200 metres; the distant sternlight-without-masthead is the barge at the end of that long tow. Do not try to pass between the two white sterns — alter to pass well astern of the barge.

Traps

• Yellow towing light is the signature of towing astern, and it sits above the white sternlight. A towed barge shows no towing light.
• Count masthead lights: two vertical = tow ≤200 m; three vertical = tow >200 m. The extra light and the daytime diamond both key off the same 200 m threshold.
• Inland pushing/alongside = two yellow towing lights (no sternlight); International pushing/alongside = ordinary sternlight. Do not blend the two rule sets.
• A composite unit is lit as one ordinary power-driven vessel — no towing light at all.