Question 1

You are OOW on a 25,000 GT general cargo vessel making 12 knots in open waters. You observe a vessel displaying two black balls in a vertical line and two all-round red lights at night. What is this vessel and what are your obligations?

Accepted Answer

NUC VESSEL — CM RESPONSE: The vessel displaying TWO BLACK BALLS (day) / TWO ALL-ROUND RED LIGHTS vertical (night) is a NOT UNDER COMMAND (NUC) vessel. COLREG Rule 27(a): "A vessel not under command shall exhibit two all-round red lights in a vertical line where they can best be seen; two balls or similar shapes in a vertical line where they can best be seen." DEFINITION (Rule 3(f)): "Not under command means a vessel which through some exceptional circumstance is unable to manoeuvre as required by these rules and is therefore unable to keep out of the way of another vessel." Typical causes: main engine failure; steering gear failure; loss of power. YOUR OBLIGATIONS: (1) YOUR VESSEL MUST KEEP CLEAR: a NUC vessel cannot take avoiding action. The NUC display is an advisory signal — YOU must manoeuvre. Rule 18(a): "A power-driven vessel underway shall keep out of the way of: a vessel not under command." (2) EARLY AND SUBSTANTIAL ACTION: Rule 16 — "Every vessel which is directed to keep out of the way of another vessel shall, so far as possible, take early and substantial action to keep well clear." (3) MONITOR CLOSELY: even if CPA is safe, continue to monitor. A NUC vessel may drift with current or alter if she partially regains power; (4) VHF: brief communication to confirm her situation and intentions may be appropriate; (5) CALL MASTER: at night in a crossing or overtaking situation with a NUC vessel — consider calling master. The situation could deteriorate rapidly if she is drifting; (6) ADDITIONAL LIGHT: if the NUC vessel is also making way — she shows sidelights in addition to the red lights. Rule 18 hierarchy (give-way order): A power-driven vessel underway keeps clear of: NUC; RAM; CBD; sailing vessel; vessel fishing. Among themselves: overtaking gives way to overtaken; port gives way to starboard (crossing); head-on both alter to starboard. NUC vs anchored (option C): two black balls in a vertical line = NUC. ONE black ball = anchored (Rule 30). A critical distinction. An anchored vessel also displays a white anchor light (all-round), not red lights. Two ALL-ROUND RED LIGHTS are the NUC night signal. Rule 18 hierarchy rationale: a NUC vessel genuinely cannot manoeuvre. Expecting them to give way is dangerous and pointless — they cannot comply. The rules therefore place the burden on vessels that CAN manoeuvre to stay clear of those that CANNOT. The principle of reduced manoeuvrability. NUC making way: a vessel with engine failure but still moving (from momentum or tidal current) must still display sidelights (green/red) because she is making way. This helps other vessels assess the aspect. The NUC signals are ADDITIONAL to normal lights when making way. Master call decision: at night, with a NUC vessel ahead, in confined waters, or when CPA is under 1nm — the master should be called. The NUC vessel may be drifting in an unpredictable direction. The situation has greater uncertainty than normal traffic.

Question 2

You observe a vessel displaying a ball, diamond, ball in a vertical line and red-white-red all-round lights. What type of vessel is this and what lights does she show at night when making way?

Accepted Answer

RAM VESSEL — IDENTIFICATION AND LIGHTS: The vessel displaying BALL-DIAMOND-BALL (day) and ALL-ROUND RED-WHITE-RED (night) is RESTRICTED IN ABILITY TO MANOEUVRE (RAM). COLREG Rule 27(b): "A vessel restricted in her ability to manoeuvre, except a vessel engaged in mineclearing operations, shall exhibit: three all-round lights in a vertical line where they can best be seen. The highest and lowest of these lights shall be red and the middle light shall be white; three shapes in a vertical line where they can best be seen. The highest and lowest of these shapes shall be balls and the middle one a diamond." WHEN MAKING WAY ADDITIONALLY: masthead light(s), sidelights, and sternlight — in addition to the RAM signals. TYPICAL RAM VESSELS: a dredger; a vessel engaged in surveying or hydrographic work; a vessel engaged in buoy laying operations; a cable-laying vessel; a vessel conducting replenishment at sea (RAS); a tug engaged in a towing operation that severely restricts her ability to manoeuvre; a vessel engaged in diving operations; a minelayer. YOUR OBLIGATIONS: Rule 18(b): "A power-driven vessel underway shall keep out of the way of a vessel restricted in her ability to manoeuvre." Your vessel must keep clear. A RAM vessel with obstruction on one side: Rule 27(d) — if the vessel's ability to manoeuvre is restricted due to work on one side, she shows additional lights/shapes to indicate the safe side to pass. Day signals — fishing vs RAM (option B): fishing vessels under Rule 26 show a CONE (apex down) by day and ALL-ROUND GREEN over RED lights at night. The Rule 27 RAM signals (ball-diamond-ball / red-white-red) are completely distinct. This is a frequently confused pair in oral exams. Rule 18 hierarchy continuation: power-driven vessels keep clear of: NUC, RAM, CBD, fishing, sailing. RAM is above CBD in the hierarchy — a power-driven vessel gives way to RAM. However, RAM does NOT take precedence over a vessel not under command. NUC has the same or higher priority. Practical RAM examples examiners probe: (1) Cable-laying vessel — significant RAM; crosses traffic schemes; (2) RAS (Replenishment At Sea) — the supply vessel and the warship being replenished both display RAM; (3) Dredger with pipe over the side — additionally marks the side where passing is dangerous (Rule 27(d)); (4) Diving support vessel — Rule 27(e) additional signals; (5) Minesweeper — Rule 27(f) additional three all-round green lights, one at each end of the sweep. RAM on one side additional signals: Rule 27(d) — when the work creates a hazard on one side, the RAM vessel shows: two additional all-round red lights on the side of the obstruction and two all-round green lights on the safe-to-pass side. A dredger with a suction pipe extending to starboard would show: red-red to starboard, green-green to port.

Question 3

You are approaching a narrow channel and observe a vessel displaying three all-round red lights vertically and a cylinder shape by day. What is this vessel and how should you respond?

Accepted Answer

CBD VESSEL — CM RESPONSE: A vessel displaying THREE ALL-ROUND RED LIGHTS vertically (night) and a CYLINDER (day) is CONSTRAINED BY DRAUGHT (CBD). COLREG Rule 28: "A vessel constrained by her draught may, in addition to the lights prescribed for power-driven vessels, exhibit where they can best be seen three all-round red lights in a vertical line, or a cylinder." DEFINITION (Rule 3(h)): "constrained by draught means a power-driven vessel which, because of her draught in relation to the available depth and width of navigable water, is severely restricted in her ability to deviate from the course she is following." KEY DISTINCTION: CBD is not the same as RAM. RAM is restricted by the nature of the work. CBD is restricted by the depth of water — the vessel cannot safely alter course because she would ground. YOUR RESPONSE: (1) Rule 18(d): "A power-driven vessel shall, except in circumstances where Rule 9 and 10 apply, keep out of the way of a vessel constrained by her draught." (2) In a narrow channel (Rule 9): CBD in a narrow channel is a particularly complex situation. Rule 9(b) — vessels under 20m or sailing vessels shall not impede the passage of a vessel that can only navigate within a narrow channel or fairway. A large vessel in a narrow channel may effectively be both CBD and the vessel that cannot safely depart from the channel; (3) PRACTICAL RESPONSE: give maximum clearance. Alter course or reduce speed early. Do NOT expect the CBD vessel to manoeuvre — she may literally be unable to do so without grounding. Three red lights (option B): three red lights all-round in a VERTICAL LINE is CBD under Rule 28. A DISTRESS signal is different: Rule 37 — distress signals include flames, continuous sounding of fog signal, square flag + ball, MAYDAY radio call, orange smoke, and others. Three red lights in a vertical line is NOT listed as a distress signal. Understanding the distinction matters — misidentifying a CBD vessel as in distress creates confusion and false SAR response. Cylinder vs anchor ball (option D): ONE black ball = vessel at anchor (Rule 30). A CYLINDER = CBD vessel (Rule 28). These are distinct shapes. The cylinder is a three-dimensional cylindrical can shape — unmistakable as different from a ball. Rule 18 hierarchy — CBD position: the Rule 18 hierarchy is: NUC → RAM → CBD → Fishing → Sailing → Power-driven. CBD is given lower priority than NUC and RAM but higher priority than fishing and sailing. A CBD vessel IS a power-driven vessel — but with severely restricted manoeuvring ability. Why CBD is different from NUC: a NUC vessel has a MECHANICAL failure. A CBD vessel is functioning normally but PHYSICALLY CANNOT deviate from her course without grounding. The distinction is: NUC = can't manoeuvre due to breakdown; CBD = won't manoeuvre because doing so causes grounding. In both cases, other vessels must keep clear. The pilot vessel in a narrow channel: a large container ship constrained by draught in a dredged channel entering a major port is perhaps the most common real-world CBD scenario. Tugs and small craft are obligated under Rule 9 to keep out of the way.