At night, you observe: two red lights in a vertical line with no other lights. Identify the vessel, what rule governs your obligations, and describe the encounter.

A. TWO RED VERTICAL LIGHTS — VESSEL NOT UNDER COMMAND (NUC): IDENTIFICATION: Rule 27(a): "A vessel not under command shall exhibit: (i) where they can best be seen, two all-round red lights in a vertical line; (ii) where they can best be seen, two balls or similar shapes in a vertical line; (iii) when making way through the water, in addition to the lights prescribed in this paragraph, sidelights and a sternlight." VESSEL NOT UNDER COMMAND: a vessel that through some exceptional circumstance is unable to manoeuvre as required by these Rules. Examples: steering failure, main engine failure, mooring equipment failure that has immobilised the vessel. WHY NO OTHER LIGHTS: if the NUC vessel is NOT making way — only two all-round red lights. No sidelights, no masthead lights. This indicates the vessel is stationary or drifting. THE HIERARCHY (RULE 18): a NUC vessel is at the TOP of the right-of-way hierarchy. ALL other vessels give way to a NUC vessel. Your vessel MUST give way. YOUR OBLIGATIONS: (1) GIVE WAY: immediately commence avoiding action; (2) APPROACH WITH EXTREME CAUTION: the vessel may be drifting — approaching too close could mean the vessel moves unexpectedly; (3) VHF CALL: attempt contact on VHF 16 — establish if they need assistance, what their condition is, which way they are drifting; (4) WIDE BERTH: give a wide berth. NUC vessels may have anchor deployed, mooring lines in water, rescue boats in water; (5) MASTER: call the master immediately.

B. Two red vertical lights is the signal for a vessel at anchor. Treat it as an anchored vessel and alter to pass clear.

C. Two red vertical lights indicates a vessel constrained by draught (CBD). She is the stand-on vessel — proceed but give way as required.

D. A vessel showing two red vertical lights at night with no other lights is the give-way vessel under Rule 18. Maintain your course — she must give way.

A. RULE 8 — CHARACTERISTICS OF PROPER AVOIDING ACTION: RULE 8 APPLIES TO ALL VESSELS in a potential collision situation, regardless of which rules govern the encounter (crossing, overtaking, head-on). The characteristics: (1) EARLY: action taken in ample time — not waiting until close quarters. With 30 minutes to CPA and 10nm, early action is available. Rule 8(a): action shall be taken "in ample time"; (2) BOLD AND SUBSTANTIAL: Rule 8(b): action shall be "large enough to be readily apparent to the other vessel observing visually or by radar." Small incremental alterations (5° at a time) do not meet this standard. The other vessel must be able to see a CLEAR alteration on their radar; (3) POSITIVE: not just an alteration but a committed and maintained course to the clear; (4) RESULT IN PASSING AT A SAFE DISTANCE: Rule 8(d): the action must result in passing at a safe distance. A 0.5nm CPA in busy waters may be adequate; in open ocean — some companies require 2nm minimum CPA; (5) MAINTAIN THE ALTERATION: do not return to the original course until clearly past and clear; (6) AVOID DANGEROUS COMBINATIONS: Rule 8(c): if necessary to avoid collision or to allow more time — reduce speed or take all way off. Speed reduction alone or combined with course alteration is a valid manoeuvre; SPECIFIC CASE (0 CPA, 30 min): Give way vessel should alter significantly to starboard (if crossing, overtaking, or head-on) — aim for CPA of at least 1-2nm and confirm on radar before resuming original course; (7) RULE 8(e): "necessary to pass at a safe distance".

B. Alter course 5° to starboard at once. A 5° alteration is the standard safe minimum under Rule 8 and will be noticed by the other vessel.

C. Wait until CPA reduces to 1nm before altering. Early alteration wastes sea room and may confuse the other vessel about your intentions.

D. Sound five short blasts on the whistle and maintain course. The danger signal is the correct COLREG action when a collision is developing.

A. STAND-ON VESSEL OBLIGATIONS — RULES 16 AND 17: RULE 17 — INITIAL DUTY: the stand-on vessel shall "maintain her course and speed" to allow the give-way vessel to take action. This stability of action allows the give-way vessel to predict the stand-on vessel's position. RULE 17(a)(ii) — MAY ACT: when it becomes APPARENT that the give-way vessel is not taking appropriate action — the stand-on vessel "may take action to avoid collision by her manoeuvre alone." This is a PERMISSION — not yet an obligation. This trigger point is a matter of professional judgement — typically when the stand-on vessel can see that the give-way vessel has not altered AND CPA is becoming dangerously small. RULE 17(b) — MUST ACT: when the stand-on vessel determines that collision "cannot be avoided by the action of the giving way vessel alone" — the stand-on vessel "shall take such action as will best aid to avoid collision." This is the MANDATORY action trigger. At this point — the stand-on vessel MUST act. The action must be: (a) not an alteration to port for a vessel on the port side (Rule 17(c)); (b) bold and substantial; (c) early enough to be effective. SEQUENCE IN THIS SCENARIO: (1) Monitor CPA trend; (2) Sound danger signal (Rule 34(d)) when doubt exists; (3) If no response — consider taking avoiding action under Rule 17(a)(ii); (4) When collision cannot be avoided by give-way alone — MUST act under Rule 17(b); (5) Do NOT turn to port toward a vessel on your port side (Rule 17(c)).

B. As stand-on vessel, you must maintain course and speed under all circumstances until the vessels actually collide. Altering course is always the give-way vessel's responsibility.

C. Sound one short blast and alter to starboard immediately when the give-way vessel fails to respond. This is the correct Rule 17 action.

D. In a crossing situation, the vessel that reduces speed first is always the give-way vessel. Reduce speed without altering course.