Underwater Blades

A prototype power station featuring RP blades is running in a northern Norway strait. Hammerfest Strom s 120 tonne submerged turbine uses similar principles to a wind turbine, with 10 m long glass reinforced plastic (GRP) blades capturing the energy of tidal currents. The installation is located in a narrow strait where the current speed is both fast and uniform. 

Access is much more of a challenge than for wind turbines, and therefore the turbines are built with a modular design allowing critical components to be lifted out of the water for maintenance or repair. The plant generates 700,000 kWh of power per year, which is enough electricity for 35 homes. (Website www.e-tidevannsenergi.com). 

Wind turbine blades represent one of the success stories for the RP industry with increasing market demand for longer blades. This has caused designers to incorporate carbon fibers adding stiffness, while blade manufacturers are moving away from wet lay-up processes to ensure that the several tonnes of materials that make up a blade can be processed safely and quickly. As a result the raw materials have changed from wet-lay up systems to prepregs and both wet and dry infusion materials (Chapters 4 and 5). 

Within this rapidly altering environment, there is the need to continually reduce costs and increase output. As final refinements are made to the process and materials, the focus switches to the mold as a means to deliver further improvements. At present blade molds incorporate several common features as follows  

1 two or three robust blade mold shells fabricated fi om RP materials, often formed over a male plug of the blade shape 

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Another important consideration for marine propeller design is cavitation, the rapid formation and then collapse of vacuum pockets on the blade surface at high speed, and its contributions to losses in propulsive efficiency. The phenomenon can cause serious damage to the propeller by eroding the blade surface and creating high frequency underwater noise. Cavitation first became a serious problem in the late nineteenth and early twentieth centuries... 

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