You are approaching a port entrance. You observe a large vessel stationary in the channel showing: three black balls in a vertical line. What is this vessel, what does she show at night, and what is your immediate action?

A. Three black balls in a vertical line: VESSEL AGROUND — Rule 30(d). A vessel aground displays three black balls in a vertical line in addition to (or in some cases instead of) anchor lights. At night, Rule 30(d): a vessel aground exhibits the two anchor lights (white all-round forward higher and aft lower) PLUS two all-round red lights in a vertical line (Rule 30(d)(ii)). Immediate action: do NOT proceed into the channel — the grounded vessel may be blocking the navigable channel; call the master immediately; contact the port authority/VTS on the port working VHF channel to get information on the status and whether the channel is open; monitor Ch 16 for any Mayday or Pan-Pan; use radar and chart to identify whether there is a navigable passage around the vessel or another access route. Do not attempt to assist with towing without proper equipment and authority.

B. Three balls in a vertical line means the vessel has three anchors deployed — she is using all her ground tackle. This is a precautionary signal in a channel with poor holding ground.

C. Three black balls indicate a fishing vessel with three lines of nets deployed. This is the international signal for a vessel with extensive gear in the water.

D. Three vertical black balls is the dredger shape. The vessel is dredging the channel approach — the balls indicate three active dredge heads working simultaneously.

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.