Annex I: where the lights and shapes go.

What is COLREGs Annex I?

The technical detail behind Part C. Rule 20(e) requires the lights and shapes specified in the rules to comply with Annex I, which sets out their positioning and technical details in fourteen sections.

Section 1 defines 'height above the hull' as height above the uppermost continuous deck. Sections 2 and 3, vertical and horizontal positioning and spacing of lights. Section 4, the direction-indicating lights of fishing vessels, dredgers and vessels engaged in underwater operations. Section 5, screens for sidelights. Section 6, shapes. Section 7, colour specification. Section 8, intensity. Sections 9 and 10, horizontal and vertical sectors. Section 11, non-electric lights. Section 12, the manoeuvring light. Section 13, high-speed craft. Section 14, approval — by the appropriate authority of the flag state.

How high must the masthead light be?

On a power-driven vessel of 20 metres or more, the forward masthead light — or the only one, if she carries one — is not less than six metres above the hull. If her breadth exceeds six metres, it is not less than her breadth, but it need not be more than 12 metres above the hull (section 2(a)(i)).

On a power-driven vessel of 12 metres but less than 20 metres, the masthead light is not less than 2.5 metres above the gunwale (2(c)). Under 12 metres, the uppermost light may be lower than that (2(d)). Section 2 also requires that a masthead light carried with sidelights and a sternlight, or the all-round light of Rule 23(d)(i) carried with sidelights, be at least one metre higher than the sidelights.

How far apart are the two masthead lights?

Vertically: on a power-driven vessel of 20 metres or more, the after one is at least 4.5 metres higher than the forward one (section 2(a)(ii)), and in all normal conditions of trim the after light must be seen 'over and separate from' the forward light at 1,000 metres from the stem, viewed from sea level (2(b)). Section 13 lets a high-speed craft of 50 metres or more modify that 4.5 metres, provided the separation is not less than a formula gives.

Horizontally: when two are prescribed, not less than half the vessel's length apart, but no more than 100 metres is needed, and the forward light is not more than a quarter of the length from the stem (section 3(a)).

In practice, the height difference keeps the after light in view above the forward one, and the fore-and-aft spacing is what lets the pair work as range lights: you see them open out or close up as she alters course.

Where do the sidelights go, and why are they screened?

On a power-driven vessel, no higher above the hull than three-quarters of the height of the forward masthead light, and not so low that deck lights interfere with them (section 2(g)). At 20 metres or more they go at or near the side, and not in front of the forward masthead lights (3(b)).

Section 5: at 20 metres or more, sidelights have inboard screens painted matt black and must meet the sector requirements of section 9. Under 20 metres, screens are needed only if necessary to meet section 9.

How are lights in a vertical line spaced?

Section 2(i). At 20 metres or more: not less than two metres apart, with the lowest at least four metres above the hull. Under 20 metres: not less than one metre apart, with the lowest at least two metres above the gunwale. The height of the lowest light does not apply where a towing light is required; three lights are equally spaced.

Anchor lights: when two are carried, the forward one is at least 4.5 metres above the after one, and on a vessel of 50 metres or more at least six metres above the hull (2(k)).

Can other lights go above or between the masthead lights?

In two cases. Section 2(f) puts the masthead lights above and clear of all other lights and obstructions, with one exception: when it is impracticable to carry the all-round lights of Rule 27(b)(i) (restricted in ability to manoeuvre) or Rule 28 (constrained by draught) below the masthead lights, they may go above the after masthead light, or between the forward and after masthead lights — in which case they sit at least two metres from the centreline, athwartships (3(c)).

Section 12, notwithstanding 2(f), places the manoeuvring light of Rule 34(b) in the same fore-and-aft vertical plane as the masthead lights and, where practicable, at least two metres above the forward one — and in any case not less than two metres above or below the after one.

What size are the shapes?

Section 6: black. A ball at least 0.6 metre in diameter. A cone with a base diameter of at least 0.6 metre and a height equal to its diameter. A cylinder at least 0.6 metre in diameter and twice as high as it is wide. A diamond is two such cones with a common base. Shapes are at least 1.5 metres apart vertically.

On a vessel of less than 20 metres, smaller shapes 'commensurate with the size of the vessel' may be used, with the spacing reduced to match (6(c)).

How bright must navigation lights be?

Section 8 gives a formula for the minimum luminous intensity needed for each range, worked out for an atmospheric transmissivity of 0.8 — about 13 nautical miles' meteorological visibility. From its table: a light with a range of 2 miles needs 4.3 candelas, 3 miles needs 12, and 6 miles needs 94. Rule 22 sets which range each light needs.

Can you see a sidelight from the wrong side?

Very nearly ahead, yes. Section 9(a)(i): in the forward direction a sidelight's intensity must fall to practical cut-off between one and three degrees outside its sector, so from right ahead you may see both sidelights at once.

For masthead lights and sternlights, and for sidelights at their limit 22.5 degrees abaft the beam, the minimum required intensity is kept to within five degrees of the edge of the sector; over those last five degrees it may fall by 50 per cent, and it must reach practical cut-off not more than five degrees outside the sector (9(a)(ii)).

In practice, close to the line 22.5 degrees abaft the beam you may see a sidelight and the sternlight together. If in any doubt whether you are overtaking, Rule 13(c) says to assume you are.

What does Annex I say about all-round lights and vertical sectors?

All-round lights must not be obscured by masts, topmasts or structures within angular sectors of more than six degrees — except Rule 30 anchor lights, which need not be placed at an impracticable height to achieve it. If one light cannot manage that, two must be used, so placed or screened that they look as far as practicable like one light at a distance of one mile (section 9(b)).

Section 10 sets vertical sectors for electric lights. Except on sailing vessels underway: at least the required minimum intensity from five degrees above to five degrees below the horizontal, and at least 60 per cent from 7.5 degrees above to 7.5 degrees below. For a sailing vessel underway the second band widens: at least 50 per cent from 25 degrees above to 25 degrees below. As we read it, that is for heel — a yacht's lights tilt with her.

What does Annex I say about high-speed craft?

Section 13(a): a high-speed craft's masthead light may be lower than section 2(a)(i) requires, at a height related to her breadth, provided that seen end-on the triangle formed by her sidelights and masthead light has base angles of not less than 27 degrees. Section 13(b): at 50 metres or more, the 4.5-metre vertical separation of her masthead lights may be modified, provided it is not less than a formula gives.

In practice, a high-speed craft's lights can sit lower and closer together than a conventional vessel's, so their spread is a weaker clue to her size — and she will close the range quickly.

How might Annex I come up in an MCA oral?

It may come up as a figure to give, or as the reason behind something you see. Examples of the kind of question to be ready for:

“Why is the after masthead light higher than the forward one, and by how much?”

“What size is a ball shape, and how far apart are shapes hung?”

“On a 15-metre motor yacht, how far apart must two lights in a vertical line be?”

“From right ahead you can see both sidelights of another vessel. Is something wrong?”

“Why is a sailing vessel's vertical light sector wider?”

“A vessel shows her red-white-red lights between her two masthead lights. Is that allowed?”

Where do candidates go wrong on Annex I?

The common slips: giving the 4.5-metre figure as the horizontal spacing rather than the vertical; forgetting that the forward masthead light need not be higher than 12 metres above the hull, or the two lights more than 100 metres apart; quoting the 20-metre spacings for a smaller vessel; and assuming the height of a vessel's lights always tells you her size.