Concern rises following re-investigation of Dongedijk: following an investigation into the...

The 93m Dongedijk capsized in perfectly calm weather when the vessel had just left Port Said. The Dutch Shipping Council investigated the accident and concluded that the ship was overloaded and that IMO stability criteria issues were not being met. Later, the captain and first officer were blamed

Although there is no dispute about these conclusions, the Dutch Ministry of Transport asked DUT to broaden the investigation into the hydrodynamic safety of small container vessels.

The project re-investigated the Dongedijk incident and also analysed the capsize risk in adverse weather conditions. The first phase, which consisted of calculations and numerical simulations, found that the design of the vessel is critical in a maximum load condition. Stability does not increase when the heel angle increases from 10 to 20. The combination of overloading, trim and changing course, caused water to flow on deck at only 5 of heel; this reduced the stability of the ship significantly.

In addition, water accumulated on the aft part of the main deck due to the speed of the vessel. Both effects were sufficient for the ship to heel more than 20. Containers were submerged and began to fill with water. Water also flowed into the engine room through vent openings.

Model experiments vital

Simulations were carried out to assess the stability of the ship sailing in waves. The loading condition was such that it satisfied all IMO stability criteria. As a result of studies into the capsize risk of frigates, MARIN has many years' experience in this area. FREDYN, the resulting software, was used to investigate the capsize probability.

Results suggest that the risk is higher than expected and also higher than deemed acceptable. The primary cause of simulated capsize events is the loss of stability when a wave, with a length approximately that of the ship, passes the vessel from astern and the crest is amidships.

The Ministry of Transport has been notified. MARIN strongly recommends verifying findings through model experiments, because numerical calculations can never be 100% reliable and because these conclusions clearly suggest that present day stability regulations may not ensure the safety of the ship in all conditions.