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CUTTING THE RISK OF VESSEL CAPSIZE AT SEA

Tuesday, January 21, 2020 

Totem Plus of Israel believes it has the answer to the real risk of large cargo vessels capsizing - an online stability measurement system that relies on actual measurements rather than possibly flawed calculations.

The company cites the total loss of the PCTC Golden Ray in September 2019, the capsize of the cattle ship Queen Hind in November 2019 and the grounding of the HoeghOsaka in 2005 as sharing one common factor: the accident happened very shortly after leaving berth. The MAIB report of the Hoegh Osaka clearly identified the cause, which can be attributed to nearly all such accidents: “…having departed port with inadequate stability”.

What is the reason that ships leave port without adequate stability, and what can be done to prevent it? Can ships measure stability, and not rely on assumptions? Online Stability by Totem Plus offers a solution.

Container ships, for example, have to rely on weight declaration by the shipper and trust the port operators that the containers loaded are indeed those declared. Car Carriers have very short stays in port and rapid stowage plan alterations can go unnoticed. And all vessels may have incorrect weight of liquids in tanks, for various reasons. Wrong data, when entered into the loading Instrument, will result in wrong GM which means that the actual stability of the ship is not as the officers believe, and in some cases can endanger the vessel.

Online Stability measures the GM by a dedicated automatic system that can carry out a quick 'inclining experiment'. The procedure involves moving ballast from one side of the ship to the other and back, listing the vessel to about 1 degree either side. This allows the resulting GM to be deduced from the amount needed for this small heeling angle. The whole process is carried out after cargo operations are completed, and takes 20 minutes or less - not a significant delay to any ship. The measured GM should be compared with the calculated GM from the loading instrument, and any significant deviation should be checked thoroughly as it means something is wrong.

Further, losing stability during a voyage is a major risk; examples of possible causes are fuel usage, cargo going overboard, ballast operations and more. Log Carriers for example are known to lose stability from water absorbed in logs on deck. Possibly the most prominent example is the case of the Cougar Ace, that lost stability and heeled to 60 degrees when ballast was pumped out during a pacific crossing in 2006.

The Online Stability system offers automatic online measurement of stability during actual sailing, in addition to the 'before leaving the berth' simulation. Prudent captains can check stability throughout the voyage, by using Online Stability to automatically and continuously measure GM, by careful monitoring of the ship’s rolling period, as the GM is directly related mathematically to this period. If the GM is out of allowed limits or changes without apparent reason, an alert is given.

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