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The SEA Clam Technology

The SEA-Coventry wave energy team developed the first SEA Clam concept from 1978 onwards and tested the straight spine version on Loch Ness in 1982. This was declared by the Chief Scientist of the time as the most promising device to arise out of the national wave energy programme and to have the greatest potential for further development. This potential for further development was realised in 1984 when a large model of a circular version of the SEA Clam was tested on Loch Ness. The new configuration improved the productivity of the device by a factor of three with the same structural weight as the previous straight version. This remarkable improvement in performance was reflected in the predicted cost of power generated that was by far the lowest of the floating devices at the time.

1982 tests on Loch Ness of the straight SEA Clam

The early circular configuration of the SEA clam was a simple device that used the displacement of air to extract energy from sea waves. Twelve air chambers, the outer faces of which are formed by flexible rubber membranes, were placed around a floating ring structure. Differential wave action moved the membrane in and out forcing the air to be interchanged between chambers. Wells turbines placed in the manifolds between the air chambers extracted power from the air flow. The rigid torus structure, 60 m diameter and 8m deep, acted as a stable reference body and was designed to be moored a few kilometres offshore. Typically, a 25 MW scheme deployed off the west coast of Scotland would feature 10 SEA Clam units and produce over 50GWh per year of electricity.

SEA Clam wave energy converter model under test on Loch Ness

Following the successful test programme, full scale designs were carried out by experienced marine companies and economic hull structures were developed in steel and concrete. Detailed costings were produced and the energy capture efficiencies optimised by computer modeling. The design had advanced to the stage where full scale trials were considered.

Designs of the SEA Clam in Steel and Concrete

Development of the SEA Clam continued until the 1992 National Review of Wave Energy by Tom Thorpe on behalf of the former Department of Trade and Industry. This intensive review concluded that the electricity generation cost of the SEA Clam would be 8p/kWh, at 8% discount rate, making it the leading and most competitive floating device. Furthermore, the SEA Clam had potential of a much greater resource than the shore-based devices favoured at the time.

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