Rule 23. Lights of a power-driven vessel underway

The base set every other configuration is counted from: two masthead lights in line (the after one higher), sidelights and a sternlight.

Set

Forward masthead, after masthead higher, green to starboard, red to port, white sternlight.

Tell

Two white mastheads: the forward one lower, the after one higher. Bow-on they are almost in one vertical line, and the more her aspect opens the wider they separate horizontally. Two whites strictly in a vertical line on one mast are the mark of towing, not of size.

In fog

One prolonged blast at intervals of not more than 2 minutes. If stopped: two prolonged blasts.

Gives way

To vessels not under command, restricted in ability to manoeuvre, engaged in fishing, and sailing vessels.

Range

Masthead 6 miles, sidelights and sternlight 3 miles.

The same, but the second masthead light is optional: usually you see one white masthead, sidelights and a sternlight.

Set

Masthead, sidelights, sternlight. Second masthead optional.

Tell

One white light high up plus a coloured sidelight: a medium power-driven vessel.

In fog

One prolonged blast every 2 minutes at most.

Range

Masthead 5 miles, or 3 miles if she is under 20 m.

Instead of masthead and sternlight she may show one all-round white light plus sidelights.

Set

All-round white (visible from every direction), green and red sidelights.

Tell

An all-round white with no second white: a small vessel. From astern you see the white only, no colours.

Offset

On a vessel under 12 m the white light may be off the centreline if fitting it on the centreline is impracticable.

Range

White 2 miles, sidelights 1 mile: she can be spotted very late.

One all-round white light is enough. Sidelights are shown if practicable.

Set

All-round white. Sidelights if practicable.

Tell

A lone white light with no colours: neither her course nor her aspect can be read, so leave a wide margin.

In fog

She must make some efficient sound signal at intervals of not more than 2 minutes.

The normal power-driven set plus an all-round flashing yellow light.

Set

Masthead lights, sidelights, sternlight, all-round flashing yellow.

Tell

A flashing yellow light: her speed can be very high and closing is fast.

Flash

120 flashes per minute or more.

The normal power-driven set plus a high-intensity all-round flashing red light.

Set

Masthead lights, sidelights, sternlight, all-round flashing red.

Tell

A bright flashing red: a WIG craft. Taking off and in flight she keeps well clear of all vessels.

On the water

On the surface she is an ordinary power-driven vessel.