Sea Science: Technology to ease danger of submerged containers

Aug 11, 2017 by Scott McDowell

Sea Science: by Scott McDowell

Boaters and professional captains alike know that one of the most dangerous hazards at sea is colliding with a partially submerged shipping container that has fallen from a container ship. The severity of such an impact and the large number of reported container losses each year create a sobering impression of innumerable containers lurking in the ocean and releasing tons of floating debris.

Ninety percent of packaged cargo is transported by container ships, approaching $5 trillion worth of goods per year. The majority of containers are 20 feet long and are called TEUs (twenty-foot equivalent units) by the shipping industry. About 120 million TEUs were shipped in 2013 alone, and ocean transport increases annually.

Although container ships are the safest and most economical means of cargo transport, container losses do occur. From 2008 through 2013, an average of 546 containers were lost at sea per year, just during the course of normal operations. This equates to one lost for every 220,000 transported — certainly a low loss percentage.

Sometimes there are additional losses due to catastrophic maritime storms that skew the statistics. In 2011 and 2013, for example, two container ships broke up: one off New Zealand with 900 containers lost, and the other in the Indian Ocean with 4,293 lost. The latter, a 1,037-foot vessel built in 2008, was the largest container ship ever lost. When adding these two catastrophic losses to the routine losses in normal operations from 2018 to 2013, the average for that six-year period rises to 1,411 containers lost per year.

Loaded containers have considerable air space inside and therefore do not sink immediately when lost over the side. Some stay neutrally buoyant for days or months, posing major collision risk to underway vessels. Recovery of floating containers in the ocean is impractical, so it is best if they sink rapidly, intact and with contents inside. From a marine environmental standpoint, the worst-case scenarios are for containers to open at the surface or to sink rapidly and implode, releasing buoyant material that will reach the sea surface.

New designs of scuttling valves are being proposed for container installation. These would allow seawater entry near the bottom of floating containers and air release at the top, resulting in sinking within a few hours with no floatable debris released. With more than 100 million containers in use today, it would take years for retrofits to be implemented, but such valves would reduce floatable debris.

Intercontinental cargo transport by container ships continues to increase, and with the June 2016 opening of the wider lane in the Panama Canal, larger ships continue to be built. The canal now accepts vessels 1,200 feet long, 160 feet wide and 50 feet deep — vessels capable of transporting 13,000 TEUs. Dozens of container ships were constructed to this specification in recent years, each capable of transporting the equivalent cargo of 20 pre-World War II freighters.

There are 10 even larger container ships being constructed in 2017, with individual capacity over 20,000 TEUs. The 193-foot beam of the OOCL Hong Kong already prevents her passage through the widened Panama Canal, but the floating behemoths in this new size class are highly cost effective for freight transport via the Asia-Europe route.
The trend of larger container ships, along with the scrapping of hundreds of smaller (less than 5,000 TEU) vessels, has resulted in a newer fleet of approximately 5,300 vessels. The average vessel age is roughly 10 years compared with 25 to 30 years for tankers, bulk carriers and freighters. This has resulted in a safer container fleet, as well as improved guidelines for onboard stowage and lashing of containers aboard vessels.

The El Faro freighter, which sunk in October 2015 during Hurricane Joaquin off the Bahamas, was only 790 feet in length and carrying 33 crew, 391 containers, plus trailers and cars. It is possible that its 40-year service record contributed to construction fatigue.

Scott E. McDowell has a doctorate in ocean physics, a 100-ton Merchant Mariner license, and is author of Marinas: a Complete Guide, available at Comments are welcome below.