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WHAT HAPPENS TO CONTAINERS LOST OVERBOARD? HOW LONG DO THEY FLOAT?
Extract from ISCO-775 newsletter:
February 15 – We reviewed the typical causes and legal aspects of container collapse cases in June. In this article we address what happens to the containers once they enter the sea. How long do containers stay afloat? Is there any basis in fact for the myth that they “hover” below the surface?
The World Shipping Council’s 2020 report estimates that an average of 1,382 containers are lost at sea each year. The figure is based on a survey of the WSC members that represent 80% of the global vessel container capacity. The WSC assumed for the purpose of the analysis that the container losses for the 20% of the industry’s capacity that is operated by carriers that did not participate in the survey would be roughly equivalent to the losses reported by the responding carriers representing 80% of the industry’s capacity. The report, however, was issued before the One Apus stack collapse in December 2020 that resulted in the loss of more than 1,800 containers in the Pacific Ocean.
For how long will a container float? -Well, how long is a piece of rope?
Empty containers will eventually sink as they are not truly watertight. The question of how much time a container needs to sink is, of course, impossible to answer in a simple way – there are too many variables. The timespan depends on the type of cargo, the type of container and its permeability and resilience. However, the most determining factor is the extent of structural damage to the container after hitting the sea surface.
Some containers sink immediately, while there are stories of containers floating across the Atlantic – in one case, taking 15 months to cross the Atlantic from the Caribbean to Spain.
Once in the sea, water will enter through vents and seals. However,containers laden with lightweight, low density and buoyant cargoes can float for years even when holed and waterlogged. The cargo itself may have enough uplift to keep the container unit
Reefer containers are naturally tighter by nature for securing the correct airflow and atmosphere when carrying temperature sensitive cargoes. A reefer box may float until it is broken up, so damage during the incident, sea conditions and wave action will decide how much time before the reefer sinks.
Experience suggests that containers falling onto the sea from lower heights tend to float longer than containers falling from heights. The explanation is, of course, that the chance of containers falling from heights suffering structural damage is far greater compared with containers falling from lower heights.
In practice, this means that containers falling from small coaster vessels and barges can often be recovered prior to sinking. Containers falling from mega oceangoing boxships will often sink almost immediately after touching the sea surface. Hellenic Shipping News /
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