John Armstrong of from UK firm TidalStream says: “Even simple tasks such as replacing a circuit board or checking a sensor would require recovery of the whole turbine and its removal to base. The offshore wind turbine record, which involves site visits several times a year, suggests that the goal of fit-and-forget for tidal turbines, which see loads as great or greater, will remain unfulfilled.”

TidalStream’s 10 MW, deep-water Triton tidal power system, which was successfully trialled at 1:23 scale in May 2009, could be easier to access and maintain than offshore wind applications.

Each tidal power generating unit has 6, 20 m diameter tidal turbines mounted on twin floating vertical booms tethered to a gravity base on the seabed.

Armstrong explains: “The attachment to the base is hinged in all three planes so that the platform can swivel around to follow the tide, flex up in response to wave loadings and rotor thrust, and roll over into a maintenance position with individual turbines out for the water for access.”

After a 30 minute de-ballasting operation, the booms rotate to become the hulls of 1200 t catamaran, providing a highly stable work platform.