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

Rule 24 Owns Tug-and-Tow Night Recognition

Harbor and near-coastal Master 100 routes constantly share water with tugs towing astern, tugs pushing barges, and alongside tows. Rule 24 replaces ordinary single-vessel Rule 23 masthead logic with a vertical masthead stack, adds the yellow towing light for astern towing, and assigns lights and shapes to the tow itself. On Q100 (90%), examiners reverse these facts into "what lights does the towing vessel show when the tow exceeds 200 meters?" stems. Miss the 200-meter threshold or the yellow over white stern stack and you lose free points.

Rule 24(a) — Power-Driven Vessel Towing Astern

A power-driven vessel when towing shall exhibit:

1. Instead of the single masthead arrangement of Rule 23(a)(i)/(ii): two masthead lights in a vertical line. When the length of the tow, measuring from the stern of the towing vessel to the after end of the tow, exceeds 200 meters, three such lights in a vertical line.
2. Sidelights.
3. A sternlight.
4. A towing light in a vertical line above the sternlight (yellow; same characteristics as a sternlight but yellow).
5. When the length of the tow exceeds 200 meters, a diamond shape where it can best be seen (day signal).

Tow-length table (astern)

Length of the tow is not the length of the tug. It is the total span from the tug's stern to the after end of whatever is being towed — barge string, disabled yacht, or dredge pipeline section. A short harbor push is usually ≤200 m; a long coastal hawser tow of multiple barges often exceeds 200 m.

The yellow towing light

From astern at night, an ordinary power-driven vessel shows a white sternlight. A vessel towing astern shows yellow over white (towing light above sternlight). That is one of the cleanest exam discriminators in Part C. Do not place the yellow towing light on a vessel that is merely power-driven, fishing, or at anchor.

Rule 24(b) — Composite Unit

When a pushing vessel and a vessel being pushed ahead are rigidly connected in a composite unit, they shall be regarded as a single power-driven vessel and exhibit the lights prescribed in Rule 23. No special two-or-three masthead towing stack, no yellow towing light for that composite picture — treat the unit like one ship. Exam trap: candidates who always answer "two mastheads because it is a tug and barge" fail when the stem says rigidly connected composite unit.

Rule 24(c) — Pushing Ahead or Towing Alongside

A power-driven vessel when pushing ahead or towing alongside, except in the case of a composite unit, shall exhibit:

1. Instead of Rule 23 masthead lights: two masthead lights in a vertical line.
2. Sidelights.
3. A sternlight.

Note what is missing compared with Rule 24(a): there is no third masthead for "long push," and the yellow towing light of paragraph (a) is the astern-towing signature. Pushing/alongside uses the two-masthead vertical pair. (Inland Rules add certain special flashing lights for some towing/pushing situations on inland waters — know that Inland may differ, but the International core of two vertical mastheads for push/alongside remains a Q100 staple.)

A power-driven vessel to which 24(a) or 24(c) applies must also comply with the second masthead requirement of Rule 23 when she is 50 m or more in length (the after, higher masthead in addition to the towing stack forward as arranged by the rule).

Lights of Vessels Being Towed — Rule 24(e)/(f)

Vessel or object being towed astern (general case)

Shall exhibit:

• Sidelights
• A sternlight
• When the length of the tow exceeds 200 meters, a diamond shape where it can best be seen

The tow does not show masthead lights of a free power-driven vessel; it shows the "being towed" picture so others know it is not self-propelled traffic.

Groups pushed or towed alongside

Any number of vessels being towed alongside or pushed in a group shall be lighted as one vessel:

• A vessel being pushed ahead, not part of a composite unit, shall exhibit at the forward end, sidelights.
• A vessel being towed alongside shall exhibit a sternlight and at the forward end, sidelights.

Practical reading for a Master passenger vessel

If you see a vertical stack of two or three white mastheads on a tug-like craft and a yellow-over-white stern aspect, expect a tow astern and leave room for the full length of the hawser and barges — not just the tug. Cutting between tug and tow is a classic collision and exam disaster scenario. By day, a diamond on tug and/or tow means the tow exceeds 200 m — plan your pass with that entire length in mind.

Comparison: towing configurations

Impracticable and Special Cases (awareness)

Rule 24 also addresses vessels/objects that cannot exhibit prescribed lights (inconspicuous partly submerged tows, vessels not normally engaged in towing that must take another vessel in tow in emergency). For Master 100 Q100, the examinable core remains the 200 m threshold, two vs three mastheads, yellow towing light, composite unit = Rule 23, and diamond for long tows. If a stem describes an emergency short tow by a vessel not fitted for towing, the rule contemplates showing the lights of Rule 24 only as practicable and may require illuminating the tow — do not invent a perfect three-masthead stack on a dinner-cruise boat that has none.

Master Scenario: Crossing a Coastal Tow

You run a 49-passenger near-coastal sightseeing vessel. At dusk a tug shows three masthead lights in a vertical line, sidelights, and from a quarter aspect you later confirm yellow over white aft. Behind the tug on a long hawser are barges. Interpretation: power-driven vessel towing astern with tow >200 m. Action mindset: give the entire tow string a wide berth; do not cross between tug and barges; treat CPA against the whole system. By day the same unit would show diamonds. Contrast: a ship-shaped unit with ordinary Rule 23 mastheads and no yellow towing light may be a composite integrated tug-barge — still large and constrained, but not the classic hawser-tow light code.

Exam Framing for Q100 (90%)

Memorize the phrase set: two mastheads ≤200 m, three if >200 m; measure tow from tug stern to after end of tow; yellow towing light above sternlight for astern towing; push/alongside = two mastheads; composite unit = Rule 23; tow shows sidelights, sternlight, and diamond if >200 m. Master passenger scenarios reward the candidate who leaves sea room for the invisible length of the hawser, not only the tug's radar paint.