Lights and shapes

At night you do not see the ship, you see a pattern of coloured lights, and that pattern is a language. It tells you three things: what kind of vessel she is, what she is doing (under way, towing, fishing, stopped) and which side of her you are looking at. Whoever reads the lights well knows at once whether to give way and where the other vessel is heading. In the figure the same power-driven vessel is seen from ahead and from astern: the lights change, not the ship.

Two terms need to be clear from the start. 'Underway' does not mean 'moving': a vessel is underway when she is not at anchor, made fast to the shore or aground (Rule 3(i)), so she can be underway even when stopped in the water. 'Making way' means moving through the water. 'Restricted visibility' means fog, mist, falling snow, heavy rainstorms, sandstorms or any other similar causes (Rule 3(l)). The order of study is: the arcs of visibility first, then the power-driven vessel, then the variations for each special case.

Before learning the individual vessels you must learn the arcs, that is, from which directions each light can be seen. In the figure the vessel is seen from above, bow at the top: the masthead light (white) covers 225° towards the bow, the two sidelights (green to starboard, red to port) 112.5° each, and the sternlight (white) 135° towards the stern. The boundaries are marked at 22.5° abaft the beam: beyond that line you see only the sternlight. Together the arcs complete the full circle.

An all-round light is visible over the full 360°, with no sectors. The towing light is yellow and has the same characteristics as the sternlight.

This is the 'base' vessel: all the others are variations of her, so it pays to fix her well in mind. In the figure, seen from ahead, you see a white light at the top (the masthead light, on the centreline) and below it the green and red sidelights; from the starboard side you see the white and the green. Aft there is a white sternlight. Under 50 m a single masthead light is enough: the second one, higher and abaft the first, is optional.

A flashing light is one that flashes 120 times a minute or more, like the yellow light of an air-cushion vessel in the non-displacement mode. An all-round light, on the other hand, is visible over 360° and, on small craft, can replace the masthead light and the sternlight.

From 50 m upwards there are two masthead lights: the second is higher and further aft than the first, as the figure shows from starboard and from ahead. Sidelights and sternlight stay the same. The minimum range changes too: so large a vessel must be seen from further away, 6 miles for the masthead lights and 3 for the others. Smaller vessels have shorter ranges, and a vessel of exactly 12, 20 or 50 m must fit lights with the greater range.

If you use the engine to drive the boat you change category: you are no longer a 'sailing vessel' (Rule 3(c)), even with the sails up. What counts is propelling machinery being used: an engine running in neutral does not change your category. In the two steps of the figure, at night you show the lights of a power-driven vessel (Rule 23); by day a black cone, apex downwards, shown forward where it can best be seen (Rule 25(e)). It is one of the most frequent mistakes: people still think of themselves as 'under sail' and show the wrong lights.

The tug is recognised by two things. From ahead, instead of the single masthead light, two white lights in a vertical line; they become three if the tow exceeds 200 m, measured from the stern of the tug to the after end of the tow. From astern, a yellow towing light above the white sternlight: in the figure this is the view from astern, and from there the masthead lights and the sidelights are no longer seen. The yellow light has the same characteristics as the sternlight. With a tow of more than 200 m, by day, there is also a diamond shape.

Shapes tell you by day what lights tell you at night, and they are always black, shown where they can best be seen. The table gathers them: two balls for a vessel not under command, ball-diamond-ball for restricted in her ability to manoeuvre, a cylinder for constrained by her draught, one ball forward for a vessel at anchor, three balls for a vessel aground, two cones apexes together for fishing, a diamond for a tow of more than 200 m, a cone apex downwards for a sailing vessel under power and, for diving operations on small vessels, a rigid replica of flag 'A'.

Shapes are black. A ball has a diameter of not less than 0.6 m; a cone has a base diameter of not less than 0.6 m and a height equal to its base; a cylinder has a diameter of at least 0.6 m and a height of twice its diameter; a diamond shape consists of two cones with their bases together. The vertical distance between shapes is at least 1.5 m. On vessels of less than 20 m, smaller shapes commensurate with the size of the vessel may be used. One last rule closes the section: a seaplane or a WIG craft that cannot exhibit lights and shapes in the prescribed positions shall exhibit them as closely similar in characteristics and position as is possible (Rule 31).