Iron ore fines with a failing can test at the loading berth
MV Gulf Pioneer (Supramax, 33,000 t deadweight) is at anchor off Bandar Abbas to load 27,500 t of iron ore fines in bulk for a Far East discharge port. The shipper's declaration lists the cargo as Group A under the IMSBC Code, moisture content 10.8 per cent, transportable moisture limit 11.2 per cent, and attaches a certificate of moisture content and TML dated nine days ago. During the pre-loading inspection the chief officer finds the stockpile surface glistening, with free water standing in the tyre ruts, and 18 mm of rain fell at the terminal two days earlier. A can test on a sample taken 30 cm below the surface shows the cargo flowing and a film of water appearing within a minute of tapping. The shipper's surveyor says the certificate is valid, that the rain only wetted a surface crust, and that the vessel will lose the loading slot if she does not start within four hours. The forecast is for further showers.
1. May loading begin? Give the regulatory basis and the master's powers under the IMSBC Code.
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No. Loading should not start.
Grounds
- Certificate age. For Group A cargoes the certificate of moisture content and TML must be dated within seven days of the commencement of loading. This one is nine days old and is invalid on age alone, regardless of what it says.
- Rain since sampling. Eighteen millimetres of rain after sampling invalidates the moisture figure; moisture is not uniformly distributed in a stockpile and is typically higher near the surface and at the base, exactly where the grab will take it.
- Supplementary test. The can test is the Code's own field check. A sample that flows and shows a water film after tapping indicates moisture at or above the flow moisture point, whatever the laboratory number says.
- Visual evidence. Standing water in the ruts and a glistening surface are the classic precursors of liquefaction.
The master's powers and duties The master must not accept a Group A cargo without a valid declaration and certificate, and may refuse, stop or suspend loading where the cargo appears wet or does not correspond to the documents. The correct sequence is to refuse, require fresh sampling at the depth being loaded by an approved laboratory with the shipper's surveyor witnessing, obtain a new certificate within seven days, and re-run the can test at the ship's rail before each shift. Issue a letter of protest, and notify the manager, DPA, charterer and P&I. Loss of a loading slot is not a reason to sail a ship that may capsize; the master's judgement prevails and the company must be seen to support it.
2. Explain what the TML and the flow moisture point mean, and how a Group A cargo can put a ship over even though she left port with a positive GM.
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Definitions The flow moisture point (FMP) is the moisture content at which a sample liquefies under the Code's prescribed test. The transportable moisture limit (TML) is the maximum moisture content accepted as safe for carriage, taking the FMP and applying a margin (roughly 90 per cent of the FMP). A cargo is acceptable only when its actual moisture content is below the TML, and the can test is the shipboard check that the sample really is.
Mechanism Iron ore fines contain fine particles and void water. Under vibration from loading, the main engine and sea motion, the grains rearrange into a denser packing, pore water pressure rises, and the shear strength of the mass falls to zero in a localised zone: it behaves as a liquid. In passage, the ship's motion drives moisture upward, so a wet slurry layer forms under a drier crust. Every roll walks the slurry to the low side, generating a large free-surface moment. A few thousand tonnes of slurry shifting ten metres is tens of thousands of tonne-metres of heeling moment, which appears as a sudden, unexplained list.
Why the GM does not save you The intact GM may still be positive; the list comes from a moving free surface that was not in the departure condition. It cannot be pumped out, trimmed back or corrected at sea, and it tends to progress: each roll adds to the list until the deck edge immerses, water enters and the ship goes over. Many total losses have followed exactly this pattern.
3. Assuming the cargo is eventually re-tested and loaded, set out the precautions the master should require for the voyage.
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Loading Load only against a fresh, valid certificate and a satisfactory can test at the ship's rail; stop loading in rain and cover or reject wetted cargo. Trim the cargo to the hatch boundaries and to a level surface with no peaks or voids, so slurry cannot collect in one corner. Record the final moisture certificate, the can test results and any stoppages.
Stability and free surface Plan ballast so that at sailing all tanks are either full or empty. No slack tanks with a large free surface, and every transfer finished before departure. Keep the departure GM comfortably above the IMO minimum of 0.15 m, with an intact stability check against the IS Code criteria, so that some loss of GM can be absorbed.
Voyage Do not surface-ventilate a Group A cargo; it does not dry the body of the cargo and can worsen moisture migration. Keep hatches shut and check soundings, drafts and list at least daily, preferably each watch. Never enter a cargo hold: these cargoes deplete oxygen and can produce a dangerous atmosphere. Weather-route to avoid heavy weather and beam seas, reduce speed or alter course to limit rolling, and pre-plan a course change if the list begins to develop. Have the engine and steering ready, brief the crew on the warning signs, keep the distress and abandon plan current, and notify the manager and charterer of any change in the cargo condition, with a full record of observations.