Rhine blockage cleared by Mammoet

Mammoet Maritime recovered a 105 metre ship from the River Rhine in Germany after it sank and blocked downstream shipping for weeks.

On 13 January 2011, the Waldhof capsized and sank, with the loss of two lives. The ship was carrying 2,400 tonnes of concentrated sulphuric acid from BASF's plant in Ludwigshafen, to Antwerp in Belgium. The resultant blockage blockage created a backlog of more than 400 vessels.

Mammoet deployed 25 operatives and engineers from bases in the Netherlands and Germany. With them, they brought two sheerlegs, a crane pontoon, a tug and a pusher tug, winch pontoons and specialized equipment for dealing with the hazardous sulphuric acid.

The company stabilised the tanker by positioning wire ropes underneath it so it could be supported by the sheerlegs Amsterdam and Grizzly. Holes were then drilled through the hull to analyse the contents of the seven acid tanks.

It was discovered that chemical reactions had released hydrogen gas in the tanks. This posed a serious explosion hazard so Mammoet's specialists flushed the tanks with nitrogen gas to displace the hydrogen. following that, the tank contents were investigated. This showed that, due to the ingress of river water, there was a layer of dilute acid floating on top of the concentrated acid.

Submersible pumps were lowered through the 500 mm holes in the hull to mix the acid and obtain a uniform concentration. Mammoet personnel transferred about 550 tonnes of acid from the Waldhof to a tanker pontoon.

Due to distortion of the Waldhof's hull, it was decided, in consultation with the authorities, that it would be safer to discharge most of the remaining acid into the river, under an environmental permit.

The discharge had a negligible environmental impact, according to Mammoet, as the flow rate was controlled and a monitoring vessel nearby tested the acidity of the water in the Rhine.

On 13 February the Waldhof was refloated by pumping water from the tanks and righted using the sheerlegs. The vessel was then moved to a mooring nearby and handed over to the owners on 17 February.
Shipping authorities will investigate the cause of the accident.