Competition in container transport led to the design of ships with lower GT, that carry more containers on deck than in enclosed cargo spaces. The tonnage-based dues for feeders are charged only for the cargo carried in enclosed spaces (cargo holds), while those stowed on deck are free from dues. As a result the feeders’ holds are kept as small as possible with a (too) low freeboard. It is an irony that the earning space, such as deck cargo space, is omitted from tonnage whereas desirable features such as crew space or forecastle or double-hull envelope are included. Ports, as always attentive on their earnings, since more and more cargo are being carried on deck, have started using other means than GT or NT to recover the dues. For container ships, many ports are using TEU as the basis, thus it was after all unnecessary to develop stupid rules so we are now stuck with a generation of unstable and therefore unsafe ships. Another reason for building of these minimized ships was that they could sail with three less crew.
Unstable due to small depth/cargo hold, low freeboard with a very small angle of deck edge immersion so that with a small list there is already water on deck and the large number of containers on deck. Add to that the fact that 10 - 20% of the containers are overweight. For a normal container ship this is not a direct big problem but for ships balancing on a knife point it can become vital like with the Dutch feeder Dongedijk which had in total 150 tons of overweight on deck and capsized in August 2000 near Port Said.
However, the overweight was not the only cause of the capsize. The ship also had a trim of 1.60 m and with a heel of only 2° to 6° water came on deck and also filled the gangways with tens of tons of sea water. After a rudder command the ship heeled and capsized.
All problems are gone if feeders got one more container layer in the hold and one less on deck. A result would also be a much larger freeboard and a safe and stable ship.
The 500-TEU feeder Deneb , while loading on 11 June 2011 in the Spanish harbor of Algeciras, suddenly capsized. The cause was too many light containers low in the ship and too many overweight containers high on deck. Of 150 containers 92 were overweight, in total 241 tons. A number of containers were 200 - 600% overweight! Hence the SOLAS VGW certificate requirement these days which were developed due to the sinking of the MSC Napoli in 2007, the capsize of the Deneb in 2011 and the sinking in July 2013 of the MOL Comfort in the Indian Ocean.
Investigation report of the capsizing of mv Deneb.