personal submarine, concrete submarine, the submarine provides not only a considerable diving depth of 300m, it also provides good light conditions and a dry living space inside that is at least at the same comfort level as any sailing or motor yacht. - In many aspects it is even better as there is no movement due to wave action and hot or cold weather conditions are equalized as the water around the hull maintains inside climate stable. Maintainance cost is similar or lower to a sailing yacht of same size.