 While the aft sponsons act as trimaran sponsons do, the front sponsons do not touch the water normally; only if the ship rolls to one side do they provide added buoyancy to correct the roll.BMT Group, a shipbuilding and engineering company in the UK, has proposed a fast cargo ship and a yacht using this kind of hull.Multihull designs may have hull beams that are slimmer at the water surface ("waterplane") than underwater.