Question 1

As Chief Mate on watch, describe how you use AIS in collision avoidance and the critical limitations you must understand.

Accepted Answer

AIS IN COLLISION AVOIDANCE — USES AND LIMITATIONS: AIS (Automatic Identification System — SOLAS V/19 and Regulation V/18) provides: (1) STATIC DATA: vessel name, call sign, IMO number, type, dimensions, draught; (2) DYNAMIC DATA: position (from GPS), COG, SOG, heading, ROT (rate of turn); (3) CPA/TCPA CALCULATION: most ECDIS and dedicated AIS displays calculate predicted CPA and TCPA from AIS data. USES IN COLLISION AVOIDANCE: (a) Identify the other vessel by name — can call by name on VHF; (b) Get approximate dimensions (not always accurate — self-reported); (c) Confirm radar contact identity; (d) Understand the vessel type (e.g., restricted in ability to manoeuvre = extra care); (e) CPA calculation from AIS data (additional information to radar). CRITICAL LIMITATIONS: (1) AIS DOES NOT REPLACE RADAR: COLREGs Rule 7(c): "Assumptions shall not be made on the basis of scanty information, especially scanty radar information." AIS is also scanty unless cross-checked with radar; (2) POSITION ACCURACY: AIS positions come from the vessel's own GPS. If the GPS is degraded or spoofed — AIS positions are wrong; (3) NON-AIS CONTACTS: small craft, naval vessels, some fishing vessels, non-SOLAS vessels do NOT carry AIS. An AIS display showing no targets does not mean the area is clear; (4) DATA MANIPULATION: vessels can manually enter incorrect speed, course, or status information. AIS data for NUC status or draught is self-reported and may be wrong; (5) DELAYED UPDATES: AIS position update rate is typically 2-10 seconds for underway vessels. In fast-evolving situations, AIS is slower than radar; (6) NOT A COLREG TOOL: AIS is not mentioned in COLREGs. Manoeuvres must still be justified under COLREGs Rules — not "because AIS told me." Non-AIS contacts — the critical gap: the MAIB and MCA have both published guidance emphasising that AIS does not show all vessels. Specific categories typically not equipped or not required to carry AIS: (a) recreational craft

Question 2

As Chief Mate on watch in open sea, you detect a vessel 10nm ahead with zero CPA and TCPA 30 minutes. Describe the characteristics of a proper avoiding action under Rule 8.

Accepted Answer

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". The "5° is not enough" principle: Rule 8(b) specifically requires that course alterations be "large enough to be readily apparent to the other vessel observing visually or by radar." On radar, a 5° alteration is extremely difficult to distinguish from normal navigation variability over 30 minutes. A 30° starboard alteration is clearly visible as a bearing change on the other vessel's radar display. The rule of thumb: 30° alteration produces about 0.5nm change in CPA per mile of range. Radar detection of alteration: an observer on the other vessel watching the radar will see a clear change in the bearing trend if a substantial alteration is made. If the alteration is too small to detect, the other vessel will not know you are taking action — close-quarters will still develop. This is the purpose of the "bold and substantial" requirement. MAIB investigation of Rule 8: several MAIB collision reports have identified that the give-way vessel made "insufficient" alterations — the alteration was made but was too small to be effective or apparent. The avoiding vessel felt they had taken action; the other vessel was unaware of any action and continued on course. Five short blasts (option D): the five short blasts is the DANGER/DOUBT signal (Rule 34(d)) — it expresses doubt about the other vessel's intentions or signals that a vessel does not understand what another is doing. It is NOT a substitute for collision avoidance manoeuvring. Sounding five short blasts while maintaining course is useless for collision avoidance if no other action is taken.

Question 3

In a crossing situation, you are the stand-on vessel. The give-way vessel has not altered course despite your close approach. At what point and how do you act?

Accepted Answer

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)). Rule 17(c) — no alteration to port: this is one of the most important specific constraints in the COLREGs. In a crossing situation where the give-way vessel is on the STARBOARD side of the stand-on vessel (approaching from starboard) — the stand-on vessel must NOT alter to PORT. Altering to port would swing the stand-on vessel's bow toward the approaching give-way vessel — potentially making the collision more severe. The stand-on vessel's primary avoiding action in a crossing situation where the give-way is to starboard: STARBOARD alteration or SPEED REDUCTION (both swing the bow away from the approaching vessel or create more time/distance). Rule 17(b) as a legal obligation: once the stand-on vessel determines that the give-way vessel cannot alone prevent collision — Rule 17(b) makes action MANDATORY. A stand-on vessel that maintains course and speed into a certain collision because "it was my right of way" is in violation of Rule 17(b). Courts have held both vessels equally negligent in collisions where the stand-on vessel failed to take action under Rule 17(b). "Never alter until collision" (option B): Rule 17 explicitly states the stand-on vessel "may" and eventually "shall" take action. The rule was designed with exactly this scenario in mind — a give-way vessel that fails to act. Blind adherence to course/speed into a certain collision is not professional seamanship and is a COLREG violation under Rule 17(b). Sound signal and alter (option C): sounding one short blast signals an intention to alter to STARBOARD (Rule 34(a)). This is appropriate IF the stand-on vessel is altering to starboard. However, sounding one short blast without actually altering, or altering to port while sounding one blast, is a misuse of the sound signal. The signal should reflect the actual manoeuvre.