At night you observe a vessel showing a green light broad on your starboard bow and a red sidelength further aft. No masthead white light is visible. What type of vessel is this and what action do you take?

A. SAILING VESSEL IDENTIFICATION — CM: A vessel showing SIDELIGHTS (red and green) but NO WHITE MASTHEAD LIGHT is a SAILING VESSEL. Power-driven vessels must show a masthead white light under Rule 23. Sailing vessels under Rule 25 show ONLY sidelights and sternlight (no masthead white light). IDENTIFICATION: Green broad on starboard bow + red further aft indicates you are seeing her STARBOARD bow (green) and her port bow (red) — the vessel is heading roughly away from you at an angle showing both sidelights. The additional lighting scenario: Rule 25(c) — a sailing vessel may additionally carry, at or near the masthead, two all-round lights — red (upper) and green (lower). These are OPTIONAL and in addition to, not replacing, the sidelights and sternlight. Rule 25(d) — a sailing vessel under 7m may use a white torch or lantern. YOUR OBLIGATION: Rule 18(d): "A power-driven vessel shall keep out of the way of a sailing vessel." You must give way to a sailing vessel UNLESS she is overtaking you (Rule 13 still applies). COLREG BETWEEN SAILING VESSELS (Rule 12): if both vessels are sailing: (a) wind on different sides — port-tack gives way; (b) wind on same side — windward gives way; (c) port tack vessel unable to determine other's tack — give way as if other is starboard tack. YOUR IMMEDIATE ACTION: determine the sailing vessel's aspect and course. Your vessel is the give-way power-driven vessel. Alter course to pass well clear to starboard if she is on your port bow.

B. Sidelights without a masthead light indicate a vessel in distress. The sidelights indicate she may be a power-driven vessel that has lost her masthead light.

C. A vessel showing both red and green sidelights is heading directly toward you on a collision course. Take immediate action to alter to starboard.

D. Sailing vessels in open waters have no priority over power-driven vessels. Rule 18 only gives sailing vessels priority over power-driven vessels in restricted waters.

A. 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.

B. A NUC vessel is the stand-on vessel in all situations. Your vessel must maintain course and speed and allow the NUC vessel to take avoiding action.

C. Two black balls means the vessel is at anchor. You should maintain your course but pass with caution at a safe distance as anchored vessels are not give-way.

D. The NUC vessel's situation is a temporary inconvenience. The rules of the road between power-driven vessels apply normally — the vessel on the port side gives way.

A. 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.

B. Ball-diamond-ball is the day signal for a vessel engaged in fishing. At night, a fishing vessel shows red over white all-round lights.

C. RAM vessels have the right of way over all other vessels including sailing vessels. As a power-driven vessel, you must always give way to RAM.

D. Three vertical lights (red-white-red) are shown by a hovercraft operating in the non-displacement mode. This vessel should be treated as a power-driven vessel.