Maersk Sealand is actually the name of the company, not the ship. Sea-Land was the American company which started the container revolution half a century ago and were bought out by Maersk a few years back, since when a few of their ships have operated under the Maersk Sealand banner.
The whopper in the photo is heading down channel and will be bound for the Far East. Obviously there is a great imbalance of trade between East and West, with Europe's vast imports from China. A lot of containers have always had to be returned empty although there was a period when we used to send plastics and paper for recycling before the bottom fell out of that with the trade downturn. There are now a lot of boxboats laid up and a surfeit of empty containers around the world. Most of the boxes in the photo are therefore probably empty.
The containers seen on deck in the photo are the tip of the iceberg as the holds below are full of course. In order to maintain stability, they all have to be weighed and stowed accordingly. This is a very complex business as they also have to be in the correct order. The ship will load at a number of ports in Europe and discharge and backload in a number of ports in the Far East. Each container therefore has to be placed in exactly the right slot in whatever port it is loaded in to be accessible at whatever port it is discharged in. The principal UK container port is Felixstowe.
The reason they carry so many above deck is to reduce the size of the ships hull, which results in lower dues when transiting the Suez or Panama canals. A lot are lost overboard every year in heavy weather, Lloyds believes as many as 10,000. As each forty foot container is the thing which is hauled on the back of an articulated lorry, this equals the amount of freight traffic which passed through the Port of Dover on its busiest day ever.
The Emma Maersk quoted above, and her sister ships, are believed to have a capacity of 15,000 teu (twenty foot equivalent units) although Maersk likes to quote somewhat less for commercial reasons. This would equate to 7,500 forty foot containers or a higher number of forty and twenty foot units mixed, as is the norm.
I took some photos of one of this class, the Evelyn Maersk, as she passed ahead of us in the Dover Strait a couple of years ago, see url below. The Second Mate asked me to as his mum's name is Evelyn! He is in the second photo. The penultimate one shows the view from the Bridge, which is like looking down from a light aircraft, as the Emma Maersk departed from Odense fjord after leaving the builders shipyard.
http://shipsintheportofdover.fotopic.net/c1296266_1.html
