Part C — Lights and shapes

COLREGs Rule 27: Vessels not under command or restricted in their ability to manoeuvre

Rule 27 says a vessel not under command shows two all-round red lights in a vertical line (by day, two black balls), and a vessel restricted in its ability to manoeuvre shows red, white, red (by day, ball, diamond, ball).

What Rule 27 says

  1. Not under command: two all-round red lights in a vertical line; two balls by day; sidelights and a stern light when making way.
  2. Restricted in ability to manoeuvre (except mine clearance): all-round red, white, red in a vertical line; ball, diamond, ball by day; plus masthead light, sidelights and stern light when making way, or anchor lights or shape at anchor.
  3. A RAM vessel towing adds the towing lights and shapes of Rule 24.
  4. Dredging or underwater operations with an obstruction: the RAM signals, plus two all-round red lights or two balls on the side of the obstruction, and two all-round green lights or two diamonds on the side other vessels may pass.
  5. Where a diving vessel cannot show these, it shows a rigid replica of International Code flag 'A', at least 1 m high.
  6. Mine clearance: three all-round green lights or three balls; it is dangerous to approach within 1000 m.
  7. Vessels under 12 m, except those engaged in diving operations, need not show these signals. These are not distress signals.

This is a plain-English summary, not the official wording. For the exact text, see the IMO convention. In UK waters the rules are given legal force by the Merchant Shipping (Distress Signals and Prevention of Collisions) Regulations.

What it means on a yacht

'Red over red, the captain is dead': two reds means not under command. A blue-and-white flag 'A' means divers down, so slow right down and keep well clear.

Lights and shapes under Rule 27

  • Not under command Rule 27

    Two all-round red lights — 'red over red, the captain is dead'. No masthead light. Sidelights and stern light only when making way.

  • Restricted in ability to manoeuvre Rule 27

    All-round red, white, red. Masthead, sidelights and stern light when making way. Dredgers, cable layers and survey vessels show this.

  • Mine clearance vessel Rule 27(f)

    Three all-round green lights, one at the foremast head and one at each yardarm: keep 1000 m clear. By day, three black balls in the same positions.

  • Restricted in ability to manoeuvre, at anchor Rule 27(b)

    Red, white, red all-round lights plus her anchor light. Diving boats and survey vessels often show this.

Drawn from the starboard side at night, with the day shapes below. See every aspect in the lights and shapes trainer.

Practise it

Test yourself on who gives way in the free COLREGs trainer, or print the rules of the road cheat sheets for the chart table.

Other rules in Part C

Frequently asked questions

What do two red lights in a vertical line mean?

A vessel not under command: it cannot manoeuvre as the rules require, for example after an engine or steering failure. Keep out of its way.

What does ball, diamond, ball mean?

A vessel restricted in its ability to manoeuvre by the work it is doing, such as dredging, laying cable or surveying. At night it shows red, white, red all-round lights.