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Tuesday, January 23rd, 2007. Lost containers.

Shipping containers washed up on the beach at Branscombe Devon following the beaching of the MSC Napoli.jpgAn incidental hazard of the salvage of the Msc Napoli, the London registered ship carrying 2,323 containers, at the centre of a rescue operation undertook last Thursday in the English Channel on Thursday after it was disabled when the engine room flooded more than 40 miles from the Cornish coast, is the Temporary Danger Area set up around the vessel extending to a range of 3 miles and 2000 feet, after the Maritime and Coastguard Agency decided to beach the 62,000-tonne Napoli in Lyme Bay, near Sidmouth, to prevent sinking, following the structural failure as it was being towed to Portland Harbour in Dorset for a salvage operation.
In this area - a World Heritage Site and also known as the Jurassic Coast, as Mark Rainsley had written a few days ago - vessels are warned of the navigation hazard posed by some of the 50 lost shipping containers washed aboard from the ship, and now drifting afloat perhaps raising a few inches above the surface.
More that 60.000 tank container ships roam the seas and oceans, and containers fall occasionally from the ships that carry them, something that occurs an estimated 2,000 to 10,000 times each year. The event is so usual that freight from lost containers is seen by oceanographers as an  opportunity to track global ocean currents.
To prevent the navigational hazard the French Navy and Elf Aquitaine, began in 1990 an investigation which resulted in a guide to predict the behaviour of lost containers and drums that fall into the sea. A general-purpose container is not impermeable. It is estimated that an empty container in good condition fills with water and sinks in about 30 minutes.
To determine the buoyancy of containers, their type are divided into four categories (Imo 1 to Imo 4). For a given mass of the metal container. The following values are averages for the weight of the product transported, beyond which the tank container sinks. These values are to be taken as default values when accurate data are lacking.
IMO 1: 17 400 daN, or a mass of 17.4 tonnes;
IMO 2: 18 800 daN, or a mass of 18.8 tonnes;
IMO 4: 23 900 daN, or a mass of 23.0 tonnes;
IMO 5: 13 350 daN, or a mass of 13.35 tonnes.
For general-purpose containers wich are non-impermeable, tests show that they fill with water and sink approximately 20 to 30 minutes after falling into the sea.
To determine the buoyancy of a loaded container, the total volume displaced must be found, i.e.:
- The volume occupied by the goods transported (the sum of the external volumes of the cases or drums);
- The volume of the securing devices and any pallet bases (lacking this, a volume of 500 to 1000 litres should be taken for a weight of 250 to 500 daN).
- The volume of steel in the container. The weights when empty, have the following approximate values:
• 20-foot: 2 100 daN, or a mean mass of 2.1 tonnes;
• 40-foot: 4 000 daN, or a mean mass of 4 tonnes, for volumes of steel amounting to 270 litres and 500 litres respectively.
The apparent weight, the total mass and total volume are used to predict if the container would sink, the emergent and submerged volume. Given the currents and wind speed and the estimated emergent volume, vector calculation predicts the speed and drift of floating containers.

Posted on Tuesday, January 23, 2007 at 09:52PM by Registered Commenter[Ignacio Wenley Palacios] in | CommentsPost a Comment

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