Fatigue resistant large hollow rotor blade for underwater energy converter

A method of counteracting the effects of variation in static pressure acting upon a hollow rotor blade or hydrofoil extracting energy from a moving column of water or other liquid within which the rotor of hydrofoil is located, the variation in static pressure being caused by vertical movement of the rotor blades or hydrofoils through the water column, the method comprising the step of equalising the pressure inside and outside the rotor blade or hydrofoil by filling any voids within the hollow rotor blades or hydrofoils with a liquid in such manner as to allow the external surface of said rotor blades or hydrofoils to expand and contract under the influence of external static pressure variations, whereby cyclic static pressure fluctuations caused by vertical movement of the rotor blades or hydrofoils through the water column do not cause fluctuating stresses in the rotor blades or hydrofoils.

A method for filling the voids in the rotor blades or hydrofoils for devices capable of extracting energy from a moving water column whereby cyclic static pressure fluctuations caused by vertical movement of the rotor blades or hydrofoils through the water column do not cause large fluctuating stresses as a result of air-filled or gas-filled voids, comprising the step of allowing the external surface of said rotor blades or hydrofoils to expand and contract under the influence of external static pressure variations.

A turbine rotor or hydrofoil of hollow construction, comprising means for enabling equalisation of internal and external pressures arising on the blades or hydrofoil during cyclic movement of the blade or hydrofoil through a vertical distance when located in a moving column of water or other liquid.