This invention is type of dual-purpose boat, including cabin and hull. This boat is unique in that between the cabin and hull there is a lifting mechanism connecting the hull and cabin, at least one of which has been set up with a buoyancy regulating structure. This invention can be used as a regular boat, or if the cabin is lowered, this invention becomes a semi-submerged vessel that can be used for operational purposes or underwater sightseeing. When the invention enters shallow water or needs to navigate at high speed, the cabin can be raised to prevent beaching and to reduce resistance. The operation of this invention is simple and expands the single function of current boats.