The yo-yo camera is a regular camera in a waterproof housing. It is attached to the structure that I pictured in my journal. There is a long cord attached to a weight. As the ship moves very slowly along the yo-yo camera is slowly lowered with a winch. The weight is on the bottom of the sea floor. When the camera frame is pulled up the weight pulls the cord that is attached to the camera and a picture is taken at the same time that a strobe light goes off for lighting. It's a really simple design but it works really well.