The ships

The lifting into the water of the Ostrea at RDM in Rotterdam
The barrier had a revolutionary design. Many techniques had not been used before and if they had, it was not during such a large-scaled project as this one. There were no ships suitable for the construction of the storm surge barrier. For the building of the dam, several ships were designed, which were tours de force one by one. The ships were all ‘state-of-the-art’. Most of the ships were provided with a system which could automatically and very precisely determine the location of the ship. The bearing techniques for orientation were quite new. In addition, new techniques were used to identify the surface and the structure of the sea bottom. Equipment such as gyroscopes and accelerometers would have been indispensable. To process the data flows provided by the equipment, large computers were necessary.

Mytilus (mussel)

This ship made sure that the bottom of the Oosterschelde was compressed along the section were the barrier would be built. When the bottom is compressed, the sand and clay parts are compacted more closely to each other. The bottom becomes more solid. Without the work of the Mytilus, the barrier would not have been as firm. The entire compression process took place under water and continued twenty-four hours per day. The ship consists of five pontoons: a main pontoon of 18.9 metres long and four auxiliary pontoons with a total length of 32.9 metres. On the ship were lifting porches of fifty-five metres high. The lifting winches which were fixed to them had a pulling power of 120 tonnes. Vibration needles with a diameter of 2.1 metres and a length of eighteen metres were drilled into the bottom of the sea. The engine of the ship generated vibrations which were transferred into the needles. The needles transferred vibrations to the sea bottom, with a frequency of between 25 and 30 Hertz and an amplitude of 4 to 5 millimetres.   

Cardium (cockle)

Although the Ostrea was the most impressive ship of the fleet, the Cardium was the most expensive one. Nobody ever thought the ship would cost so much. The actual costs were eighty percent higher than expected. For this amount of money the Cardium carried out an important task: putting down the mats. These mats which were thirty-six centimetres thick, forty-two metres wide and two hundred metres long. The synthetic mats were filled with sand and gravel in a factory. The mat was moved to an enormous container, which was fixed to the Cardium. The mats were put on the sea bottom at a rate of ten metres every hour. An extra mat was put at the areas where the piers were to be placed. This was to protect the mats against wear, which could be developed through the opening and closure of the slides.

The Ostrea (oyster)

The Ostrea near a landing-point photographed from a bird's eye perspective
The Ostrea was the flagship of the Delta fleet. With its length of eighty-seven metres, the typical U-shape and a capability of 8,000 horsepower, it was the most impressive ship. The ship lifted the piers from the dry dock and sailed them to the place of the barrier. With the open side of the ‘U’, the ship manoeuvred around the pier. The ship could steer easily, thanks to its four screw propellers. On both sides there were two porches fifty metres high. The piers were fixed to these porches. The porches could not lift more than 10,000 tonnes however, whereas the piers weighed 18,000 tonnes. So how did the Ostrea put the piers in the right place? Fortunately, the levers did not have to lift the piers completely out of the water. The most important factor was that they did not touch the bottom of the sea during transportation. Because of the upward pressure of the water, the levers needed to provide less power.

Macoma (nun)

The Macoma viewed from the air
This pontoon, named after a shellfish, was situated exactly in front of the place where a pier would be placed. When the Ostrea had taken a pier, it moored against the Macoma. To offer the Ostrea some stability, the pontoon had a coupling mechanism with a power of six hundred tonnes. The Macoma also had a second function: an enormous vacuum cleaner was used to ensure there was no sand between the pier and the bottom. This was an extremely difficult job, because the tidal movements moved large amounts of sand each day.

Wijker Rib (fish)

This inspection ship originally plunged stone. During the construction of the Oosterschelde barrier, the Wijker Rib was multifunctional. It, among others, supported the small inspection vehicle Portunus. This vehicle was the size of a small van and could drive on the bottom of the sea with caterpillar tracks. The observations of the Portunus were transferred to the mother ship via an umbilical cord. The data was checked, processed and interpreted in the Wijker Rib.

Other ships

Jan Heymans viewed from the air
Jan Heymans
There were many more ships cooperating in the construction. The Johan V was a geotechnical reconnaissance pontoon, which was built especially for this project. It was provided with a drill and a diving bell. By means of a diving bell, samples of the sea bottom could be taken. Another ship, the Jan Heijmans, helped the Cardium place the mattresses. The Jan Heijmans was also responsible for the filling of the holes between the mattresses and the gravel. The Macoma worked together with the Sepia and the Donax I during the placement of gravel ballast mats on the bottom.