Annex I

Positioning & Technical Details of Lights and Shapes

Where lights and shapes must be placed, their dimensions, colours, intensity and sectors.

1: Definition

The term "height above the hull" means height above the uppermost continuous deck. This height shall be measured from the position vertically beneath the location of the light.

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Wording follows the International Regulations as printed in the US Coast Guard Navigation Rules handbook (2024), with British spelling, and is shortened in places. Download the rules

Read the whole of Annex I on one page

1: Definition

The term "height above the hull" means height above the uppermost continuous deck. This height shall be measured from the position vertically beneath the location of the light.

2: Vertical positioning and spacing of lights

(a) On a power-driven vessel of 20 m or more, masthead lights shall be placed: (i) the forward masthead light (or the only one carried) at a height above the hull of not less than 6 m, and if the breadth exceeds 6 m at a height not less than that breadth, but need not exceed 12 m; (ii) when two are carried, the after one at least 4.5 m vertically higher than the forward one. (b) Their vertical separation shall be such that, in all normal trim, the after light is seen over and separate from the forward light at 1000 m from the stem viewed from sea level. (c) The masthead light of a vessel 12 m to under 20 m shall be at least 2.5 m above the gunwale. (d) A power-driven vessel under 12 m may carry the uppermost light below 2.5 m above the gunwale; but a masthead light carried with sidelights and a sternlight, or the Rule 23(d)(i) all-round light carried with sidelights, shall be at least 1 m higher than the sidelights. (e) One of the two or three masthead lights prescribed for a power-driven vessel when towing or pushing shall be placed in the same position as either the forward masthead light or the after masthead light; provided that, if carried on the aftermast, the lowest after masthead light shall be at least 4.5 m vertically higher than the forward masthead light. (f)(i) The Rule 23(a) masthead light(s) shall be above and clear of all other lights and obstructions, except as in (ii). (f)(ii) When it is impracticable to carry the all-round lights of Rule 27(b)(i) or Rule 28 below the masthead lights, they may be carried above the after masthead light(s) or vertically between the forward and after masthead light(s), provided that in the latter case Section 3(c) is complied with. (g) Sidelights shall be at a height not greater than three-quarters of the forward masthead light, and not so low as to be interfered with by deck lights. (h) A combined-lantern sidelight on a vessel under 20 m shall be at least 1 m below the masthead light. (i) Two or three lights carried in a vertical line shall be spaced: (i) on a vessel ≥ 20 m, not less than 2 m apart, the lowest (except where a towing light is required) not less than 4 m above the hull; (ii) on a vessel < 20 m, not less than 1 m apart, the lowest (except where a towing light is required) not less than 2 m above the gunwale; (iii) when three lights are carried, they shall be equally spaced. (j) The lower of the two all-round lights for a fishing vessel shall be above the sidelights by at least twice the distance between the two vertical lights. (k) When two anchor lights are carried, the forward one shall be at least 4.5 m above the after one; on a vessel ≥ 50 m it shall be at least 6 m above the hull.

3: Horizontal positioning and spacing of lights

(a) When two masthead lights are prescribed, the horizontal distance between them shall be at least half the vessel’s length (need not exceed 100 m), and the forward light not more than one quarter of the length from the stem. (b) On a vessel ≥ 20 m, sidelights shall not be placed in front of the forward masthead lights; they shall be at or near the side of the vessel. (c) When the Rule 27(b)(i) or Rule 28 lights are placed vertically between the forward and after masthead light(s), they shall be at least 2 m from the fore and aft centreline in the athwartship direction. (d) When only one masthead light is prescribed for a power-driven vessel, it shall be exhibited forward of amidships; except that a vessel under 20 m need not exhibit it forward of amidships but shall exhibit it as far forward as is practicable.

4: Direction-indicating lights (fishing, dredgers, underwater operations)

(a) The light indicating the direction of outlying gear (Rule 26(c)(ii)) shall be 2–6 m horizontally from the all-round red and white lights, not higher than the Rule 26(c)(i) white light and not lower than the sidelights. (b) The lights/shapes indicating the obstructed and passing sides for dredging or underwater operations (Rule 27(d)(i) & (ii)) shall be at the maximum practical horizontal distance, never less than 2 m, from the Rule 27(b) lights/shapes, and never higher than the lower of those three.

5: Screens for sidelights

The sidelights of vessels of 20 m or more in length shall be fitted with inboard screens painted matt black, meeting Section 9 of this Annex. On vessels under 20 m the sidelights, if necessary to meet Section 9, shall be fitted with inboard matt black screens. With a combined lantern using a single vertical filament and a very narrow division between the green and red sections, external screens need not be fitted.

6: Shapes

(a) Shapes shall be black and of the following sizes: (i) a ball: diameter not less than 0.6 m; (ii) a cone: base diameter not less than 0.6 m and a height equal to its diameter; (iii) a cylinder: diameter at least 0.6 m and height twice its diameter; (iv) a diamond: two cones as in (ii) with a common base. (b) The vertical distance between shapes shall be at least 1.5 m. (c) In a vessel under 20 m, smaller shapes commensurate with her size may be used and the distance apart correspondingly reduced.

7: Colour specification of lights

The chromaticity of all navigation lights shall lie within the CIE boundaries defined by these corner coordinates: • White: x: 0.525, 0.525, 0.452, 0.310, 0.310, 0.443 / y: 0.382, 0.440, 0.440, 0.348, 0.283, 0.382 • Green: x: 0.028, 0.009, 0.300, 0.203 / y: 0.385, 0.723, 0.511, 0.356 • Red: x: 0.680, 0.660, 0.735, 0.721 / y: 0.320, 0.320, 0.265, 0.259 • Yellow: x: 0.612, 0.618, 0.575, 0.575 / y: 0.382, 0.382, 0.425, 0.406

8: Intensity of lights

(a) Minimum luminous intensity is given by I = 3.43 × 10⁶ × T × D² × K⁻ᴰ, where I is intensity (candelas), T the threshold factor (2 × 10⁻⁷ lux), D the luminous range (nautical miles), and K the atmospheric transmissivity: 0.8 for prescribed lights (≈ 13 NM meteorological visibility). (b) Derived values (K = 0.8): 1 NM → 0.9 cd; 2 → 4.3; 3 → 12; 4 → 27; 5 → 52; 6 → 94 cd. Maximum intensity should be limited to avoid undue glare.

9: Horizontal sectors

(a)(i) In the forward direction, sidelights must show the minimum required intensities, decreasing to practical cut-off between 1° and 3° outside the prescribed sectors. (a)(ii) For sternlights, masthead lights, and (at 22.5° abaft the beam) sidelights, the minimum intensity is maintained up to 5° within the Rule 21 limits; from 5° within it may fall by 50% up to the prescribed limits, then decrease steadily to practical cut-off at not more than 5° outside them. (b) All-round lights shall be located so as not to be obscured by masts, topmasts or structures within angular sectors of more than 6°, except anchor lights, which need not be at an impracticable height.

10: Vertical sectors

(a) For electric lights (except on sailing vessels): (i) at least the minimum intensity from 5° above to 5° below the horizontal; (ii) at least 60% of it from 7.5° above to 7.5° below. (b) For sailing vessels: (i) at least the minimum intensity from 5° above to 5° below; (ii) at least 50% of it from 25° above to 25° below. (c) For non-electric lights, these specifications shall be met as closely as possible.

11: Intensity of non-electric lights

Non-electric lights shall, so far as practicable, comply with the minimum intensities specified in the Section 8 table.

12: Manoeuvring light

Notwithstanding paragraph 2(f), the Rule 34(b) manoeuvring light shall be in the same fore-and-aft vertical plane as the masthead light(s) and, where practicable, at least 2 m vertically above the forward masthead light, but not less than 2 m above or below the after masthead light. Where only one masthead light is carried, it shall be where it can best be seen, at least 2 m vertically apart from the masthead light.

13: High-speed craft

Section 13 lets high-speed craft carry the masthead light lower, related to their breadth, and modify the 4.5 m masthead separation on craft of 50 m or more, within limits set out in the official text.

14: Approval

The construction of lights and shapes and the installation of lights on board the vessel shall be to the satisfaction of the appropriate authority of the State whose flag the vessel is entitled to fly.

A training aid, not the official text. The COLREGs are an IMO convention, and your national authority publishes the version that applies in its waters. Check the rules themselves before you rely on them at sea. Download the rules.