You are navigating a channel at night. Ahead you observe a vessel showing three all-round lights in a vertical line: red (top), white (middle), red (bottom). The vessel appears stationary. What is this vessel and what action do you take?

A. Three all-round lights: red — white — red (top to bottom): this is a VESSEL CONSTRAINED BY DRAUGHT (CBD) — Rule 28. The vessel cannot deviate from its course due to insufficient depth in relation to its draft. It is showing the optional CBD lights under Rule 28 in addition to ordinary lights. Rule 28: "A vessel constrained by her draught may, in addition to the lights prescribed for power-driven vessels in Rule 23, exhibit where they can best be seen three all-round lights in a vertical line, the highest and lowest of which shall be red and the middle light shall be white." Obligation: Rule 18(d) — power-driven vessels shall keep out of the way of a vessel constrained by draught. Actions: keep well clear; do not attempt to pass ahead; if in a narrow channel, ensure you are on the correct side of the channel and not impeding the CBD vessel. By day: a CBD vessel may display a cylinder (black).

B. Three lights red-white-red indicates a vessel with lights on deck for cargo work. It is a vessel conducting cargo operations at anchor with deck working lights — treat as an anchored vessel.

C. Three lights red-white-red is not a recognised COLREGs light combination. The vessel may have a lights malfunction. Contact on VHF to determine her identity.

D. Three vertical lights with red at top and bottom indicate a mine-clearance vessel. You must keep well clear — at least 1000m from each quarter and astern.

A. Two all-round red lights in a vertical line: this is a VESSEL NOT UNDER COMMAND (NUC) — Rule 27(a). The vessel is unable to manoeuvre as required by COLREGs due to some exceptional circumstance. Obligations: Rule 18 — all power-driven vessels must keep out of the way of a NUC vessel. You are the give-way vessel regardless of aspect or crossing/overtaking geometry. Actions: alter course and/or reduce speed early and substantially to keep clear; do NOT cross ahead of a NUC vessel. Monitor: watch for any green (starboard) or white (sternlight) becoming visible — this confirms aspect and direction of drift; watch for any additional lights (towing, dredging); check for any DSC/MAYDAY on DSC Ch70 or Ch16 — a NUC vessel may be in distress. Rule 35 fog signals for NUC: two prolonged + one short blast every 2 minutes if making way; two prolonged if stopped.

B. Two red vertical lights indicate a vessel constrained by draft. You must keep well clear but can pass ahead if the range is sufficient.

C. Two red lights in a vertical line mean the vessel is at anchor. Anchor lights are all-round white — two reds in a line indicate an anchored vessel with emergency lights on.

D. Two red lights indicates a fishing vessel with gear deployed. Maintain your course and speed as stand-on vessel; the fishing vessel must keep clear.

A. All-round red over white in a vertical line WITH sidelights: this is a PILOT VESSEL underway — Rule 29(a)(i). The red over white is the internationally recognised pilot vessel identification light. The sidelights confirm she is underway and making way. Obligations: no specific Rule 18 obligation to keep clear of pilot vessels — they are treated as power-driven vessels underway for collision avoidance purposes (Rule 18 list does not include pilot vessels). Apply normal Rules 12-17 based on aspect and situation. By day: pilot vessels display the international flag "H" (Hotel — vertical halves, white and red).

B. Red over white all-round lights indicate a trawler — the white is the towing light showing the direction of the gear, and the red indicates a vessel with nets deployed on the port side.

C. Red over white vertical lights indicate a vessel constrained by draught displaying the optional CBD lights under Rule 28.

D. Red over white in a vertical line means a vessel restricted in ability to manoeuvre (RAM). Stand-on rules apply and the pilot vessel should give way to you.