Question 1

Your post-panamax container vessel is in the Pacific in a confused sea state. The vessel begins rolling with rapidly increasing amplitude — 10°, 20°, 35° in succession with rolls at double the wave frequency. What is this phenomenon and how do you respond?

Accepted Answer

PARAMETRIC ROLLING — MASTER'S RESPONSE: PARAMETRIC ROLLING is one of the five dangerous situations in heavy weather identified in MSC.1/Circ.1228. It affects vessels with large variation in waterplane area between the bow/stern and the midship sections — particularly post-panamax container ships and large bulkers. DEFINITION: parametric rolling occurs when: (a) the encounter frequency with waves is approximately TWICE the vessel's natural roll period; (b) the vessel is heading into head seas or following seas; (c) the vessel's stability varies significantly as waves pass — the GM increases on the wave crest (large waterplane) and decreases in the trough (reduced waterplane). This creates a parametric excitation of the rolling motion. RECOGNITION: (1) Rolls develop rapidly from small to dangerously large amplitude; (2) Rolls occur at approximately half the wave encounter frequency; (3) Occurs in head or following seas — not beam seas; (4) Can reach 30-40° + in minutes; (5) Once established, self-reinforcing. RESPONSE: (1) IMMEDIATELY ALTER COURSE: change heading significantly (30-60°) to place the seas on the quarter or beam. This changes the encounter geometry and breaks the resonance; (2) CHANGE SPEED: increasing or decreasing speed changes the encounter frequency, which can break the parametric resonance; (3) DO NOT ACTIVATE STABILISERS: active stabilisers can make parametric rolling WORSE by adding energy to the roll; (4) REDUCE SPEED AND HEAD INTO SEA if necessary; (5) SECURE ALL LOOSE ITEMS: at 30-35° angle, unsecured cargo and equipment become projectiles. MSC.1/Circ.1228 five dangerous situations: (1) Surf-riding and broaching; (2) Loss of stability on wave crests; (3) Synchronous rolling; (4) Parametric rolling; (5) Shipping water on deck. All five are in the syllabus — examiners test all of them. Parametric vs synchronous rolling distinction (option B): synchronous rolling is when the wave period EQUALS the vessel's roll period — the vessel rolls once per wave. Parametric rolling is when the ENCOUNTER FREQUENCY is approximately TWICE the roll period — the parametric excitation occurs at twice the frequency of the roll. Parametric rolling is more violent and less intuitive. Both require course/speed change to resolve. Container ship vulnerability: post-panamax container vessels have significant "flare" at the bow — the bow is much wider above the waterline than at the waterline. This creates the GM variation as waves pass that drives parametric rolling. Loss of container lashings: at 30-35° roll, the lashing forces on deck containers approach and may exceed design limits. Containers can topple onto other containers or into the sea. Several major container losses (MOL Comfort, El Faro context, various partial losses) involved extreme rolling. Active stabiliser avoidance (option D): this is a critical, counterintuitive point. Active fin stabilisers apply a corrective force AGAINST the roll. In parametric rolling, the roll is driven by energy from the wave-ship resonance. Active stabilisers may add energy at the wrong phase and amplify the roll. The correct response is to change the encounter geometry (course change) which removes the energy source.

Question 2

You are Master of a 35,000 GT bulk carrier in the North Atlantic in a Force 11 storm. The vessel is experiencing heavy slamming and two deck crew have been injured. Speed has been reduced to 5 knots. Charterer is demanding continued passage. What is your command decision?

Accepted Answer

COMMAND DECISION — FORCE 11 HEAVY WEATHER: SOLAS V/34 and ISM Code Section 5.3 give the master OVERRIDING AUTHORITY on safety decisions. The charterer cannot override this. ASSESSMENT: (1) STRUCTURAL INTEGRITY: at 35,000 GT bulk carrier in Force 11 — slamming at 5 knots indicates the vessel is taking green water over the bow. Slamming causes cumulative structural fatigue and can cause hatch cover failure — potentially fatal for a bulk carrier. Inspect hatch covers and deck plating; (2) CREW SAFETY: two crew injured — this is already a safety failure. Continuing in Force 11 with injuries risks further crew harm. The master must cease activities that are causing injury; (3) CARGO INTEGRITY: bulk cargo shift risk in extreme rolling. Check cargo for signs of movement or liquefaction; (4) STABILITY: check the stability situation — in heavy weather, free surface effects from ballast movement and deck water may affect GM; COMMAND OPTIONS: (a) HEAVE-TO: turn the vessel into the sea (head-to-sea or bow slightly off) and reduce speed to minimum steerage. This dramatically reduces slamming and deck cargo stress. The vessel makes minimal progress but safety is maximised; (b) RUN WITH THE SEA: in some sea states, running before the sea at controlled speed reduces slamming but risks broaching; (c) SEEK PORT OF REFUGE: assess the nearest available port of refuge and request entry. The port of refuge decision involves: vessel structural condition; crew condition; weather forecast (will it moderate?); port availability and shelter quality; (4) COMMUNICATION: inform the charterer in writing. State the safety grounds under ISM Section 5.3. Document everything. The charterer's commercial demands do not override the master's safety authority. The command decision in heavy weather is one of the most important tests of professional judgment. It is not binary (proceed vs stop) — it requires a continuous, dynamic assessment. The key factors: (1) structural condition of the vessel; (2) crew safety and welfare; (3) cargo condition; (4) weather forecast; (5) proximity to shelter; (6) vessel's sea-keeping characteristics. Charterer authority (option B): the charterer has NO authority over safety decisions. This is stated explicitly in ISM Section 5.3 and backed by SOLAS V/34. A master who proceeds in conditions causing structural damage and crew injury at the charterer's insistence has abandoned their STCW and ISM responsibilities. The forced heave-to (option C): not necessarily the right decision either. A well-found vessel with experienced crew in open sea may be able to make headway in Force 11. The decision depends on: (a) the vessel's actual condition; (b) the forecast trend; (c) whether heaving-to creates its own hazards (proximity to lee shore, traffic). MAYDAY (option D): Force 11 + slamming + two injuries is NOT automatically a MAYDAY situation. The vessel is navigating and not in immediate danger of sinking. A MAYDAY is appropriate only when the vessel is in imminent danger of sinking or a life is in immediate danger. The correct communication is: UKMTO/MRCC notification if seeking assistance; the passage/condition report to company; MAYDAY only if the situation genuinely becomes life-threatening. Documentation of the command decision: write every assessment, every communication with the charterer, and every action taken in the log. If a formal inquiry follows — this documentation demonstrates the master's professional decision-making.

Question 3

After 36 hours in Force 10-11 conditions, your vessel has shifted cargo and developed a 7° permanent list to starboard. You are 200nm from the Azores. What is your port of refuge decision process?

Accepted Answer

PORT OF REFUGE DECISION — MASTER: A 7° permanent list indicates the centre of gravity has shifted — either cargo movement or flooding. This is a SERIOUS STABILITY SITUATION requiring immediate port of refuge consideration. DECISION PROCESS: (1) ASSESS THE CAUSE: is the list from: (a) Cargo shift (if so — is it getting worse? Can it shift further in continuing heavy weather?); (b) Flooding (is water making its way in?); (c) Free surface from shifted ballast or tank changes? (2) ASSESS THE TREND: is the list stable at 7° or worsening? A stable 7° list may be survivable in moderate conditions. A worsening list in Force 10-11 may lead to capsize; (3) STABILITY CALCULATION: run the loadicator with the assumed shifted cargo weight and position. What is the current effective GM? What is the righting arm (GZ) at current heel? Does the vessel have adequate stability reserve?; (4) WEATHER FORECAST: will the storm moderate within 6-12 hours? If yes — can the vessel safely ride it out? If no or uncertain — proceed to port of refuge; (5) ASSESS THE REFUGE PORT: (a) Can the Azores (Horta, Terceira) receive a vessel with 7° list in the current sea state? (b) Is there adequate shelter in the port? (c) Can cargo be restowed there? (d) Is a tug available for assistance if manoeuvring is compromised by the list?; (6) DECLARATION TO COASTAL STATE: contact the Portuguese maritime authority (MRCC Delgada) — request port of refuge entry. Provide vessel condition, stability status, list, cargo shift; (7) PAN PAN: in a vessel with compromised stability, transmit a PAN PAN (urgency) signal. This alerts maritime authorities without the formality of MAYDAY. 7° list from cargo shift: this is a serious situation requiring IMMEDIATE action — but not necessarily abandon ship. The master's response must be measured and analytical. At 7° list, the vessel's GZ curve has been shifted. The question is: what is the residual stability reserve? A vessel with 1.5m GM shifted to 7° may have adequate reserve. A vessel with 0.3m GM shifted to 7° is dangerously close to capsizing. The loadicator gives this answer. The worsening trend: if the list is worsening (was 3°, now 7°, still rolling heavily) — immediate port of refuge is required. The cargo will continue to shift in heavy weather until equilibrium at the new angle or until the vessel capsizes. 7° being "manageable" (option B): depends entirely on the stability reserve. This is not a generic answer — it requires calculation. Oral examiners want to see that the master uses the loadicator and makes a data-driven decision, not a "seems OK" assessment. Abandon ship (option C): premature. A 7° list in heavy weather is dangerous but not necessarily a capsizing situation. Abandoning ship in Force 10-11 seas is enormously dangerous — survival craft in these conditions have capsized. The master does not abandon the vessel unless the remaining-on-board option is worse than abandonment. Counter-ballasting (option D): this addresses the list symptom but not the cause. If the cargo has shifted — adding starboard ballast may correct the list angle but it adds weight and reduces freeboard. In continuing heavy weather, the cargo may shift further, making the next correction impossible. The longer-term solution is port of refuge and cargo restowage.