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« on: February 20, 2013, 01:08:09 AM »
Hi Dennis, Jadran and the others in this thread,
Let's face it, shipping is about economy, and as long as port dues, insurance, etc. are based on Gross Tonnage, owners will press for compromises between safety and economy.
The first vessel on the image Denis provided is unsafe by design. It is a container feeder type favoured by shipyards in the Northern Netherlands and their clients. In this design a low GT is reached by reducing the freeboard to such an extent that stability just meets the minimum allowed by the IMO Load Line Convention 1966. The tricky thing with rules, be it IMO, national or classification, is that you can design a ship where all the parameters meet the minimum as laid down in the rules. You can't call this a safe ship, however, due to its built-in vulnerability.
The experts (I'm not an expert) will remember the Dongedijk casualty back in August 2000, when she capsized shortly after leaving Port Said. The Dongedijk (IMO 9201877), built 1998, 2926 GT, 2926 dwt, l.o.a. 99,95 m, has a container capacity of 344 teu (two tiers in the hold and four tiers on deck).
The Dutch Maritime Safety Council (Raad voor de Scheepvaart) heard the naval architect Dr. Ernst Vossnack, one of its panel of experts, on the matter of stability. In essence, the Dongedijk was a "victim of the Gross Tonnage Rules", he argued. Vossnack campaigned for some years against the tonnage measurement convention rules, which have led to designs where more cargo is carried on deck than in the registered spaces below the hatches. He said the 1966 Load Line Convention was based on the ship type of the time, with a high free board. For ships like the Dongedijk an altogether new approach is needed.
The casualty occurred in a smooth sea when leaving Port Said. She fell on her beam ends because of a free surface in water ballast tanks, and also the accumulation of water on deck just forward of the bridge. Vossnack said this water came aboard because of the very low freeboard and the fact that the ship was trimmed slightly by the stern on account of the loading plan.
The ship was down to her marks when she left the Port Said terminal for the short voyage to Lattakia. As she worked up to her full sea speed she was overtaken by her own stern wave, which accumulated a mass of water around and under the aftermost container stack, which could not be seen from the wheelhouse. Altering course with a helm movement to port was sufficient to dip the deck edge and throw the ship on her beam ends. The 14 people aboard escaped by jumping overboard, as the freefall lifeboat was inoperative, and were saved by small craft in the vicinity.
A much safer design would have one extra tier of containers below deck, with the freeboard thus substantially increased. The reality, however is that such a design change would increase the gross tonnage from 2,926 gt to 3,800 gt. No shipyard could possibly sell such a design, Vossnack acknowledges.
(English text in part based on a news report in Lloyd's List, 11 December 2001)
All the best, Anton
PS: the late Ernst Vossnack, for many years head of Nedlloyd's ship design department, knew how to build a safe ship. See IMO 8503797 Norsun (now Pride of Bruges) and IMO 8501957 Norsea (now Pride of York) from 1987, which he designed for North Sea Ferries. Unlike many other ferries of this vintage they needed not be disfigured later with sponsons and duck tails for extra buoyancy.
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