Systems are described for obtaining energy, especially electrical energy, from sea waves. An elongated elastic tube device (12) floats at the sea surface (20) (or at a shallow depth under it) and extends at least partially parallel to the direction of wave propagation (D). The tube bends as a wave passes by and such tube bending stretches and relaxes SSM (synthetic stretchable material) (44, 60, 62) which generates electricity in electrodes (46, 48) when its amount of stretching changes. Electricity from power takeoffs in the tube are electronically added.