International Navigation Rules

Part C Lights and Shapes

Rule 20 Application

(a) Rules in this Part shall be complied with in all weathers.
(b) The Rules concerning lights shall be complied with from sunset to sunrise, and during such times no other lights shall be exhibited, except such lights as cannot be mistaken for the lights specified in these Rules or do not impair their visibility or distinctive character, or interfere with the keeping of a proper lookout.
(c) The lights prescribed by these Rules shall, if carried, also be exhibited from sunrise to sunset in restricted visibility and may be exhibited in all other circumstances when it is deemed necessary.
(d) The Rules concerning shapes shall be complied with by day.
(e) The lights and shapes specified in these Rules shall comply with the provisions of Annex I to these regulations.

Rule 20
For this Rule, "in all weathers" means regardless of the state of visibility, good or bad. Navigation lights may be shown at any time during the day, and most towing vessels do so. They must be shown in daytime if visibility is restricted and, of course, must be shown at night. Shapes - commonly called "dayshapes" - are for daytime use only; they should be ignored if seen at night.

The requirement of Rule 20(b) that no other lights be shown that would impair the visibility of navigation lights is most important - but have you ever seen a cruise ship all lit up?!

In order not to overly complicate the basic Navigation Rules, specifications for lights and shapes, and requirements for the placement of these on vessels, are given in Annex I. There are differences between this Annex in the International and in the Inland Rules.

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Rule 21 Definitions

(a) "Masthead light" means a white light placed over the fore and aft centerline of the vessel showing an unbroken light over an arc of the horizon of 225 degrees and so fixed as to show the light from right ahead to 22.5 degrees abaft the beam on either side of the vessel.
(b) "Sidelights" mean a green light on the starboard side and a red light on the port side, each showing an unbroken light over an arc of the horizon of 112.5 degrees and so fixed as to show the light from right ahead to 22.5 degrees abaft the beam on its respective side. In a vessel of less than 20 meters in length, the sidelights may be combined in one lantern carried on the fore and aft centerline of the vessel.
(c) "Sternlight" means a white light placed as nearly as practicable at the stern showing an unbroken light over an arc of the horizon of 135 degrees and so fixed as to show the light 67.5 degrees from right aft on each side of the vessel.
(d) "Towing light" means a yellow light having the same characteristics as the "sternlight" defined in paragraph (c) of this Rule.
(e) "All-round light" means a light showing an unbroken light over an arc of the horizon of 360 degrees.
(f) "Flashing light" means a light flashing at regular intervals at a frequency of 120 flashes or more per minute.

Rule 21
The term "masthead" light is somewhat a misnomer - this light is seldom, if ever, actually at the head (top) of the mast; that position is usually reserved for an anchor light. The masthead light may be below, well below, the head of the mast, provided that the location meets the requirements of Annex I as to its height "above the hull (gunwale)"; these heights vary according to the size of the vessel.

Note that the Inland Rules have less restrictive provisions for the masthead light and sidelights on vessels less than 12 meters (39.4 ft.) in length that do not appear in the International Rules.

The high rate of "flashing lights," 120 or more flashes per minute, is specified to prevent confusion with Quick-Flashing lights on aids to navigation, which flash at a nominal rate of 60 per minute.

The "special flashing light" is a feature of the Inland Rules only; it is used to mark the forward end of a barge pushed ahead. Note that its arc of visibility can be slightly different from a masthead light, but is always not less than 180¼.

Rule 22 Visibility of Lights

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The lights prescribed in these Rules shall have an intensity as specified in Section 8 of Annex I to these Regulations so as to be visible at the following minimum ranges:

(a) In vessels of 50 meters or more in length:

(d) In inconspicuous, partly submerged vessels or objects being towed: a white all-round light, 3 miles.

Rule 22
The basic requirement of Rule 22 is the intensity of each navigation light; this is for the guidance of the designers and manufacturers of the hardware. The stated ranges provide a necessary input into the formula used in Annex I to calculate the intensity. A light is "legal" if it meets the intensity requirement of Annex I, even though under some conditions of visibility it cannot be seen at the ranges stated in this Rule for that type of light. The stated ranges also provide guidelines for vessel operators and enforcement agencies in the field.

Both sets of Rules state the visibility requirement in terms of "miles"; this is a nautical mile even on inland waters normally using statute miles for distances. Annex I translates these visibility distances to technical measurements of luminous intensity for use in the design and manufacture of navigation lights.

The Inland Rules state a visibility requirement of two miles for a "special flashing light"; this light does not appear in the International Rules. This light is yellow, as is the light for air-cushion vessels when operating in the non-displacement mode, but the frequency of the flashes is different allowing an observer to differentiate between them.

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Rule 23 Power-driven Vessels Underway

(a) A power-driven vessel underway shall exhibit:

Rule 23
This Rule establishes what might be termed the basic requirements for navigation lights, sometimes called "running lights," for vessels underway. Subsequent Rules will cover vessels towing and being towed, vessels under sail or being rowed, fishing vessels, pilot vessels, and other categories and situations.

There are differences between the International and Inland Rules. In general, the Inland Rules provide more options and are less rigorous regarding placement.

Note that the International Rules contain a provision for craft less than 7 meters long operating at speeds not greater than 7 knots (the vessel can be capable of greater speeds, but must not be operated at more than 7 knots while using this Rule). This provision does not appear in the Inland Rules. In turn, the Inland Rules contain a special provision for vessels on the Great Lakes that does not appear in the International Rules.

Nowhere in either set of Rules does the term "range lights" appear, but the two masthead lights, where fitted on larger vessels, do form a range similar to that established by two aids to navigation. This "range" is very helpful in determining the orientation of a ship seen at a distance at night - the white masthead lights can be seen at a considerably greater distance than the red and green sidelights.

In October, 1996, Inland Rule 23(a)(i) was changed. The revised Rule eliminates the exception for vessels less than 20 meters in length; these craft must now have their masthead light located in the forward half of the vessel. The Rule is now directly comparable with the corresponding International Rule.

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Rule 24 Towing and Pushing

(a) A power-driven vessel when towing shall exhibit:

(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 in the case of a composite unit, shall exhibit:

(d) A power-driven vessel to which paragraphs (a) or (c) of this Rule apply shall also comply with Rule 23(a)(ii).
(e) A vessel or object being towed, other than those mentioned in paragraph (g) of this Rule, shall exhibit:

(f) Provided that any number of vessels being towed alongside or pushed in a group shall be lighted as one vessel:

(g) An inconspicuous, partly submerged vessel or object, or combination of such vessels or objects being towed, shall exhibit:

(h) Where from any sufficient cause it is impracticable for a vessel or object being towed to exhibit the lights or shapes 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 such vessel or object
(i) Where from any sufficient cause it is impracticable for a vessel not normally engaged in towing operations to display the lights prescribed in paragraph (a) or (c) 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 towed as authorized by Rule 36, in particular by illuminating the towline.

Rule 24
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.

For determining 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; thus, it is the sum of the length of the towline and the towed vessel.

Note carefully that the lights seen from astern of vessels pushing ahead or towing alongside are quite different in waters governed by the Inland and by the International Rules.

Note that the two masthead lights for towing vessels with tows of 200 meters or less, and the three masthead lights used with longer tows, may be shown either forward or aft on towing vessels 50 meters or more in length. If the 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.

Note that the diamond dayshape required on the towed vessel or object for tows over 200 meters in length has no corresponding light for nighttime. Note also that 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).

Shapes

Diagram of Ship Shapes A
The Inland Rule 24(a) is quite explicit, stating "a vessel when towing astern." The corresponding International Rule merely states "a vessel when towing," but this has been interpreted as meaning only towing astern. Neither the International nor the Inland Rules clearly cover the situation of more than one vessel or object being towed in line astern.

Diagram of Ship Shapes B

A reasonable interpretation of the Rules, however, can focus on the language "a vessel or object towed astern" - nothing is said about confining the requirement to the last vessel in a string. This would seem to require each vessel or object to be similarly lighted with sidelights and a sternlight. In October, 1996, Inland Rule 24(f) was changed. The requirement for the lighting of barges pushed ahead and alongside was revised. The revision reflects the situation on the Western Rivers where often multiple barges are pushed by a single power-driven vessel. The Rule is still not directly comparable with the corresponding International Rule. Note that at Rule 24(i) the International and Inland Rules "get out of step." International (i) corresponds to Inland (j), and Inland (i) has no International counterpart.