There are 2 types of instruments that can generate electricity from wave energy: floaters and sitters. Salter's Duck and Cockerell's Raft are examples of floaters and Vickers 'Duct' is an example of a sitter. The Salter�s Duck design can extract approximately 90% of the energy from a wave. It is made up of a chain of about 25 floats. As they bob up and down on the water a pump is driven and electricity is generated. Cockerell�s Raft generates electricity by placing lines of rafts at right angles to the wave front. Between the rafts are hydraulic motors or pumps, which convert the energy to high pressure that then drives the turbines. Vickers 'Duct' consists of a submerged tube in which water rises and falls. As the internal pressure changes water is squirted out and electricity generated.