An Experimental Study on the Stability of a Catamaran Boat Equipped with an Underwater Camera

A catamaran boat with two hulls and a deck is expected to be an ideal watercraft for such marine monitoring tasks. We proposed a remote-control catamaran boat that uses flexible hoses. The flexible hoses could provide both buoyant force in the sea and a flexible shape for mobility. The boat length is 2.5m and the beam is 1.3m. It has been used in the inspection of the jetty, qual wall, and drainage pipe.To expand the applications and enable underwater photography, the boat is equipped with an underwater camera. In the present study, the boat and underwater camera were connected by a flexible rope. We measured the severity of shaking (acceleration) of the boat and camera during regular waves by a water tank test. Here, one of the accelerometers was fixed to the boat to measure the acceleration of the center of gravity on the x, y, and z-axis, while another accelerometer was fixed to the underwater camera with the same arrangement. The field experiments were then carried out at Hiratsuka Port to check the operation and underwater photography performance in real sea conditions.As a result, the boat’s acceleration and vibration at rest condition depend on the wave conditions, and compared to the boat, the underwater camera, which is connected by a flexible rope, accelerates reduction. Especially, the heave acceleration of the camera is decreased remarkably. Relatively low acceleration means a better condition for taking clear underwater videos and images, which could be of great help to underwater photography. We also compared the accelerations in cruising conditions during the head wave and the following wave. The accelerations when cruising in the following wave is smaller than when cruising in the head wave. The reason for this phenomenon is that when cruising in the head wave, the boat meets more waves per unit of time than it would at rest, which reduces the wave period and intensifies vibration. For practical use, keeping the position after reaching the desired location or while cruising in the following wave can help take relatively clear images and videos.