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“Under certain conditions [fine particle cargo, containing high levels of moisture], nickel ore may become like a semi-solid or liquid, in a process termed as liquefaction. Then it starts moving like liquid inside the hold [cargo area] of a ship. If the hold is partly filled in such a condition, the effect [free surface effect] on ship stability will be bad. In this context, it may be noted that liquid cargo in bulk is carried by tanker ships, which are specially designed, considering safety requirements,” says P. Krishnankutty, Professor, Department of Ocean Engineering , IIT-Madras.
A merchant ship’s structure is supported by a steel base, the keel. If the cargo loaded or unloaded at a port causes a list to one side then on-board staff take in or pump out sea water from various ballast tanks to even the keel. Out at sea, the impact of waves can create rolling, pitching and other motions. A ship is designed to have a large self-righting capacity so it doesn’t capsize even during heavy rolling or pitching. “But a high list reduces the reserve stability considerably, which may lead to a sudden capsize of the ship,” points out Prof. Krishnankutty.
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