B2/​1997M The Cap­siz­ing of Self-pro­pelled Barge CARA at Raahe 25.5.1997

11.06.2003

The self-propelled, self-unloading barge ms CARA capsized at the dredging work area off the harbour of the city of Raahe in north-western Finland on Sunday May 25th 1997 at about 14:10. The barge, which is owned by dredging company Terramare Oy, was on it’s way from the dredger KOURA II to the offloading area.

The dredging work by Terramare Oy was nearing completion at Lapaluoto Harbour in Raahe at the date of the accident and the finishing dredging was going on in the harbour basin.

As the dredging was in final stage, the dredged cargo material was watery soil. The material was described as being ”very soft mud including much water”. It was the skipper’s responsibility to decide about the amount of cargo carried by the barge as well as to observe the loadline mark.

CARA had made trips from the dredger to the offloading area about once every hour through day and night. The driver of the dredger and the person who loaded the barge remember that it had a slight heeling angle to port when it embarked towards offloading area. The pilots at the nearby pilot station had been watching the movements of the barge, but they did not notice anything unusual,
such as heel, on this trip.

When the accident occurred, only the skipper of the barge was onboard. The skipper was very experienced in this work. He had started working for the predecessor of the company already in 1964. CARA departed from the dredger at about 14:05. The barge capsized either in a turn or immediately after it. There were no eye-witnesses for the accident. The rescue work was started immediately, because the upturned floating barge was observed by a pilot from the Raahe pilot station at 14:12. The skipper died and his body was found in the wheelhouse by a diver on the following day.

Heel of the vessel initiated by a turn led to the capsize to port. The vessel had a negative region in the stability from about six degrees of heel. In this region the heel increased without an outside heeling moment. The rate of heel accelerated simultaneously. The heel set the upper layer of the cargo to accelerating motion and with the larger heeling angle also part of the more solid cargo shifted and the stacks started to even out. When the heeling angle exceeded about 25 degrees,the cargo started flowing out to the sea from the hold.

The shift of the cargo as such, if it had happened slowly, would not have capsized the vessel, because part of the cargo would have flowed out onto the side deck and to the sea as a thin layer. Instead the cargo “collapsed” or shifted even in rotary motion. The fast heeling initiated the motion of the cargo mass as thick layer. This outflowing cargo, on the other hand, caused a reaction force, which increased the heeling moment. The heeling motion accelerated to so high a value that the vessel continued capsizing until it was upside down. Analysis showed that the capsizing was caused by the fluidity and the amount of the cargo. According to the calculations the capsizing with a very muddy cargo is possible with a mean draft of 2,27 metres, which is 16 centimetres below the permissible national loadline (traffic area domestic I).