Question 1

You are the Chief Mate on anchor watch in Falmouth Bay. Overnight wind has increased to Force 7 from the SW. How do you detect dragging and what is your response?

Accepted Answer

ANCHOR WATCH — DRAGGING DETECTION AND RESPONSE: DRAGGING DETECTION METHODS: (1) ECDIS/CHART PLOTTER ANCHOR WATCH ALARM: most ECDIS systems have an "anchor watch" function — set a circle of safe radius around the anchor position. If the vessel moves outside the circle, an alarm sounds. The radius should account for normal swinging range (scope × sin angle of swing); (2) RADAR: fixed radar range/bearing bearings from shore objects. Re-check every 15-20 minutes. If the bearing/range from a fixed object changes progressively in one direction — the anchor is dragging; (3) VISUAL: lights ashore — if they are moving in an unusual direction relative to the vessel; (4) DEPTH SOUNDER: if depth is changing significantly in a constant wind — could indicate dragging into deeper or shallower water; (5) VIBRATION: chain going taut and the vessel surging while the chain vibrates can indicate the anchor dragging. RESPONSE TO DRAGGING: (6) CALL THE MASTER AND DUTY ENGINEER: engine standby immediately. Do not wait — in Force 7, the vessel can drag quickly; (7) ENGINE TO SLOW AHEAD: use the engine to take the load off the anchor and allow it to bite again. Do not rush to full ahead — this can break out the anchor completely; (8) ASSESS: is the vessel in danger of running aground? What is the rate of dragging? (9) WEIGH ANCHOR: if dragging cannot be arrested — weigh anchor and proceed to sea or to a safer anchorage; (10) NOTIFY VTS AND MRCC: if the vessel is in danger of grounding, a PAN PAN may be required. ECDIS anchor watch circle: setting the anchor watch circle is one of the most important tasks at anchor. The radius should be approximately: scope length × sine(maximum expected swing angle). For a 6-shackle scope (150m) with 30° swing — the watch radius is about 75-80m. The ECDIS alarms when the ship's GPS position exits the circle. However — ECDIS anchor watch relies on accurate GPS. If GPS is degraded, the radar bearing method provides an independent cross-check. Force 7 and dragging: Force 7 (strong breeze, 28-33 knots) in an open bay like Falmouth Bay is a genuine dragging risk, especially for a heavy vessel with a light anchor or insufficient scope. Standard holding power formulae suggest that for many vessels in Force 7, 6-7 shackles of scope on a good holding ground is minimum. On poor holding ground (gravel, rock, weed) — more scope or a different anchorage is needed. Calling the master: a Force 7 increase during anchor watch should result in the master being called. This is not the chief mate's sole decision. The master makes the call on weighing anchor and proceeding to sea. The chief mate manages the immediate watch while the master is called. Full ahead response (option D): giving full ahead with the anchor down could: (a) put extreme load on the anchor and windlass; (b) break the anchor out of the ground entirely; (c) cause the chain to part. The correct approach is SLOW ahead with the anchor still on the ground, engine running to reduce the dragging force — then a controlled weighing of the anchor if required.

Question 2

As Chief Mate on a chemical tanker, you are planning to load benzene (UN 1114, Class 3, PG I) after carrying methanol. What segregation, tank preparation, and safety measures apply?

Accepted Answer

BENZENE LOADING AFTER METHANOL — CHIEF MATE's PLANNING: CARGO COMPATIBILITY CHECK: (1) Are methanol and benzene compatible for sequence loading? Methanol (Class 3/6.1) and benzene (Class 3) are both flammable — BUT they are not compatible in the sense that residual methanol in a benzene cargo = CONTAMINATION. Check the IBC Code compatibility matrix and the charterer's cargo compatibility requirements; (2) TANK WASHING: tanks previously carrying methanol must be thoroughly washed before benzene loading. Methanol is water-soluble and miscible — water washing followed by recirculation is appropriate. Complete drying is required as water in benzene cargo = haze/contamination; (3) BENZENE PROPERTIES (UN 1114): (a) Class 3, Packing Group I (very high flammability); (b) Boiling point 80°C, flashpoint -11°C (extremely flammable); (c) TOXIC: a human carcinogen (Group 1 IARC). Vapour exposure risk — PPE: SCBA and full chemical protection suit for all operations; (d) Vapour density 2.7 (heavier than air — accumulates in low areas); (4) MARPOL ANNEX II: benzene is Annex II Category X substance (most hazardous). Pre-washing before any discharge — MANDATORY; (5) IBC CODE SPECIAL REQUIREMENTS: benzene requires closed loading, vapour return line (vapour recovery or destruction), enclosed gauging (no open ullaging), and restricted access during loading; (6) SAFETY ZONE: 3-metre exclusion zone around manifold during loading operations. No ignition sources within 30m. IGS may not be required (benzene is non-reactive to inert gas atmospheres) but nitrogen blanket may be required; (7) EMERGENCY: EmS F-E (flammable liquids fire) and S-E (spillage). Benzene as a carcinogen: benzene is classified as a Group 1 carcinogen by IARC (International Agency for Research on Cancer). The IMDG Code and IBC Code impose additional health protection requirements beyond standard Class 3 liquid handling. Exposure limits: the UK COSHH regulations specify a Workplace Exposure Limit (WEL) for benzene of 1 ppm (8-hour TWA). This is extremely low — the vapour pressure of benzene at ambient temperature means significant benzene vapour can be present at open ullage points, manifold areas, and any open sampling. ALL operations involving benzene cargo must use SCBA and appropriate chemical protection. IBC Code Chapter 15 special requirements: Chapter 15 of the IBC Code specifies additional cargo-specific requirements for each chemical. For benzene — these include: (a) vapour emission control; (b) closed operations; (c) emergency shutdown system; (d) health monitoring for crew. MARPOL Annex II Category X: benzene is among the most strictly regulated liquid cargoes under MARPOL Annex II. Discharge into the sea of any benzene-contaminated washwater is absolutely prohibited unless processed through a compliant retention/disposal system. Pre-wash is mandatory before ANY discharge of residues in any sea area. Cross-contamination (option B): loading benzene into a tank with methanol residue creates a contaminated benzene cargo. Methanol is infinitely miscible with benzene — even small traces will reduce benzene purity below specification. Additionally, water from tank washing that is not completely dried creates a benzene/water haze that similarly renders the cargo off-specification.

Question 3

In port, a cargo hold is opened and a strong smell of chlorine is detected. The manifest shows UN 1017 (Chlorine, Class 2.3 Toxic Gas) in the lower hold. Crew members are near the hold. As Chief Mate, what do you do?

Accepted Answer

CHLORINE GAS RELEASE — EMERGENCY RESPONSE: UN 1017, CHLORINE, CLASS 2.3: (a) Extremely toxic gas — IDLH (Immediately Dangerous to Life and Health) 10 ppm; (b) Heavier than air (vapour density 2.5) — accumulates at low levels in holds; (c) Bleach-like odour detectable at 0.5 ppm — if crew can smell it, concentrations may already be dangerous. IMMEDIATE ACTIONS — FIRST 60 SECONDS: (1) SHOUT AND CLEAR: warn all crew in the vicinity to MOVE AWAY UPWIND. Do not send crew into the hold without SCBA; (2) WIND AWARENESS: position crew UPWIND of the hold opening. Chlorine disperses downwind; (3) NO IGNITION SOURCES: chlorine in combination with hydrogen (from bilge gas) could explode — no smoking, no naked flames. However, chlorine itself is not flammable; (4) CALL THE MASTER: immediate notification; (5) SOUND GENERAL ALARM: if the release is significant or risk of spread to accommodation; (6) CLOSE THE HOLD: if it can be done safely from outside without entering — secure the hold to contain the release; (7) EMERGENCY SERVICES: contact port authority and emergency services (shore fire brigade with HazMat team); (8) IMDG EmS: EmS code for UN 1017 is F-C (non-flammable gas fire) and S-U (toxic gas spillage). S-U: keep people away from damaged area. Contact 24-hour emergency advice centre; (9) EMERGENCY CONTACT: the DG manifest must show a 24/7 emergency contact. Call them immediately; (10) DO NOT VENTILATE BY BLOWING AIR INTO HOLD: this could disperse chlorine gas to adjacent areas. Chlorine toxicology: chlorine is one of the most dangerous gases that can be encountered on a cargo vessel. WWI chlorine gas attacks used concentrations above 1,000 ppm — but even at 30 ppm, severe chest pain, vomiting and pulmonary oedema occur. At 430 ppm — death within 30 minutes. Critically: chlorine is HEAVIER than air — it accumulates at the lowest point (bottom of the hold). Crew near the open hatch may not immediately appreciate the concentration at lower levels in the hold. IMDG EmS S-U: the Spillage Schedule for toxic gases (S-U) specifies: "ELIMINATE all ignition sources. STOP leakage only if safe to do so. Move people from danger area upwind. Advise competent authority of potential hazard. Contact chemical experts." "Rag over the face" approach (option C): chlorine at dangerous concentrations is immediately incapacitating. A crew member who enters a hold with chlorine vapour above IDLH using a rag as protection will quickly become incapacitated. This would turn a dangerous goods incident into a rescue situation requiring entry into a toxic atmosphere — putting additional lives at risk. The USCG and MAIB have investigated several cargo incidents where rescue attempts without SCBA resulted in rescuers also becoming casualties. Ventilation with fans (option B): ventilating by blowing air INTO the hold could spread chlorine gas to adjacent spaces, including engine room intakes and accommodation. The correct approach is to CLOSE the hold and control the release, allowing emergency services with HazMat equipment to handle decontamination. Detection threshold vs danger threshold: the detection odour threshold for chlorine is 0.5 ppm. This is BELOW occupational exposure limits (1 ppm ceiling under COSHH). Detection does not mean safe — it means dangerous concentrations may be nearby.