Abstract
The Clam is an offshore toroidal structure housing 12 air cells which are sealed from the sea by means of reinforced rubber membranes. For the desirable membrane lifetime of between five and ten years to be realised there are a number of conditions which must be met, including large vertical strength together with horizontal elasticity which permits flexibility without buckles and kinks. To achieve these characteristics two layers of reinforcing cords are laid at angles close to the vertical. This paper reports some mathematical modeling, together with small and full scale tests of membranes.