This Rule covers both "towing," which means towing astern on a hawser or cable or with the towed vessel alongside, and "pushing," which means only pushing the "towed" vessel ahead of the towing vessel.
To determine the need for different lights and dayshapes for longer tows, the distance is measured from the stern of the towing vessel to the stern of the towed vessel which is the sum of the length of the towline and the towed vessel.
The lights seen from astern of vessels pushing ahead or towing alongside are different in waters governed by the Inland and by the International Rules.
The two masthead lights for towing vessels with tows of 200 meters or less, and the three masthead lights used with longer tows, can be shown either forward or aft on towing vessels 50 meters or more in length. If multiple lights are shown forward, there will be a single, higher masthead light aft, if the two or three lights are shown aft, there will be a single, lower masthead light forward. The single masthead light is not required of shorter towing vessels, but may be shown.
The diamond dayshape required on the towed vessel or object for tows over 200 meters in length has no corresponding light for nighttime. Also the diamond shape is shown only on the towed vessel or object, and not on the towing vessel even though the triple masthead lights may not be noticeable during the day (these lights will normally be shown in the daytime, although not required by the Rules).
Rule 24 Towing and Pushing
(a) A power-driven vessel when towing astern shall exhibit:
(i) instead of the light prescribed either in Rule 23 (a)(i) or 23(a)(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;
(ii) sidelights;
(iii) a sternlight;
(iv) a towing light in a vertical line above the sternlight; and
(v) when the length of the tow exceeds 200 meters, a diamond shape where it can best be seen.
(b) When a pushing vessel and a vessel being pushed ahead are rigidly connected in a composite unit they shall be regarded as a power-driven vessel and exhibit the lights prescribed in Rule 23.
(c) A power-driven vessel, when pushing ahead or towing alongside, except as required by paragraphs (b) and (i) of this Rule, shall exhibit:
(i) instead of the light prescribed either in Rule 23(a)(i) or 23(a)(ii), two masthead lights in a vertical line;
(ii) sidelights; and
(iii) two towing lights in a vertical line.
(d) A power-driven vessel to which paragraphs (a) or (c) of this Rule apply shall also comply with Rule 23(a)(i) and 23(a)(ii).
(e) A vessel or object other than those referred to in paragraph (g) of this Rule being towed shall exhibit:
(i) sidelights;
(ii) a sternlight; and
(iii) when the length of the tow exceeds 200 meters, a diamond shape where it can best be seen.
(f) Provided that any number of vessels being towed alongside or pushed in a group shall be lighted as one vessel, except as provided in paragraph (iii):
(i) a vessel being pushed ahead, not being part of a composite unit, shall exhibit at the forward end, sidelights and a special flashing light;
(ii) a vessel being towed alongside shall exhibit a sternlight and, at the forward end, sidelights and a special flashing light; and
(iii) when vessels are towed alongside on both sides of the towing vessel, a sternlight shall be exhibited on the stern of the outside vessel on each side of the towing vessel, and a single set of sidelights as far forward and as far outboard as is practicable, and a single special flashing light.
(g) An inconspicuous, partly submerged vessel or object being towed shall exhibit:
(i) if it is less than 25 meters in breadth, one all-round white light at or near each end;
(ii) if it is 25 meters or more in breadth, four all-round white lights to mark its length and breadth;
(iii) if it exceeds 100 meters in length, additional all-round white lights between the lights prescribed in subparagraphs (i) and (ii), so that the distance between the lights shall not exceed 100 meters: Provided, that any vessels or objects being towed alongside each other shall be lighted as one vessel or object;
(iv) a diamond shape at or near the aftermost extremity of the last vessel or object being towed; and
(v) the towing vessel may direct a searchlight in the direction of the tow to indicate its presence to an approaching vessel.
(h) Where from any sufficient cause it is impracticable for a vessel or object being towed to exhibit the lights prescribed in paragraph (e) or (g) of this Rule, all possible measures shall be taken to light the vessel or object towed, or at least to indicate the presence of the unlighted vessel or object.
(i) Notwithstanding paragraph (c), on the Western Rivers (except below the Huey P. Long Bridge on the Mississippi River) and on waters specified by the Secretary, a power-driven vessel when pushing ahead or towing alongside, except as paragraph (b) applies, shall exhibit:
(ii) sidelights; and
(iii) two towing lights in a vertical line.
(j) Where from any sufficient cause it is impracticable for a vessel not normally engaged in towing operations to display the lights prescribed by paragraph (a), (c), or (i) of this Rule, such vessel shall not be required to exhibit those lights when engaged in towing another vessel in distress or otherwise in need of assistance. All possible measures shall be taken to indicate the nature of the relationship between the towing vessel and the vessel being assisted. The searchlight authorized by Rule 36 may be used to illuminate the tow.
