At night you observe a dredger showing: three all-round lights vertical (red-white-red) PLUS two green all-round lights on one side AND two red all-round lights on the other side. What do these additional lights mean and how do you pass?

A. Dredger RAM lights with side working lights: Rule 27(b)(iii) and (iv) — a vessel engaged in dredging when RAM shows the three red-white-red all-round lights (RAM lights) PLUS: two all-round RED lights on the side where the OBSTRUCTION exists (the side where the dredge pipe, spoil, or restriction is — the UNSAFE side); two all-round GREEN lights on the side where it is SAFE TO PASS. Memory: RED = DANGER (obstruction side), GREEN = GO (safe passage side). Action: pass on the GREEN side (two green lights) giving adequate clearance. Never pass on the RED side — this is where dredge pipes, anchors, spoil ground, or other equipment creates a hazard. If the dredger is in a channel, the safe side may require you to cross to the wrong side of the channel — coordinate with VTS.

B. Red lights on one side and green lights on the other indicate port and starboard lights only. The dredger is underway — red = port side, green = starboard side. Pass on the green (starboard) side.

C. The green lights indicate the dredger is working on a safe area. Pass on the RED side where no equipment is deployed. Red lights indicate the completed section of the dredged channel.

D. A dredger showing two red and two green all-round lights is in the process of moving to a new position. Neither side is currently obstructed — maintain your track and call on VHF.

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.