During the day you observe a vessel ahead that is stationary. She is displaying (from top to bottom): a black ball, a black diamond, another black ball. She is also flying a flag signal. What is this vessel and what action do you take?

A. Ball — diamond — ball (top to bottom): this is a VESSEL RESTRICTED IN ABILITY TO MANOEUVRE (RAM) — Rule 27(b). By day, a RAM vessel displays this distinctive shape. Rule 27(b)(i): "ball, diamond and ball in a vertical line." RAM vessels include: cable-laying vessels, dredgers, vessels conducting hydrographic surveys, vessels servicing aids to navigation, vessels launching or recovering aircraft, vessels replenishing at sea, and vessels involved in towing operations making it difficult to deviate from course. Obligation: Rule 18(b) — all vessels except NUC shall keep out of the way of a RAM vessel. Actions: pass well clear; do not attempt to cross ahead; if approaching a cable-layer, pass well astern (cable direction indicated by additional lights/shapes). The flag she is flying may be the code flag "D" (Delta) — "Keep clear of me" — or another relevant signal.

B. Ball, diamond, ball indicates a vessel constrained by draught. This is the CBD daytime shape and the vessel cannot move from its track.

C. Ball-diamond-ball is the international diving signal. A surface marker buoy near the vessel will indicate where divers are operating — keep 50m clear.

D. Three shapes in a vertical line always indicate a vessel at anchor. Anchored vessels display a black ball — three shapes confirm a large anchored vessel.

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.