The invention relates to an
underwater folding method for half ships, which belongs to the field of ship building installation and solves the problem that conventional lifting and a method of utilizing a
cart to move a ship cannot be suitable for folding two independently built half ships which are provided with independent reference lines. The
underwater folding method for the half ships utilizes
self weight of the half ships and difference of the
buoyancy center, the half ships are docked successively when a dock drains water outwards, the half ship docked later is docked with the half ship placed on the
pier first to serve as the standard, the fact that the distance between slits of a folding opening after docking is within a
welding slit range allowed by the standard is guaranteed so that
underwater docking of the half ships is finished; or a standard half ship is enabled not to float by the methods of ballasting, cabin breaking and the like, and after other half ships completely float, the other half ships are moved to a folding
station to perform docking and folding, and ultimately the precision requirements of a principal dimension, a
reference line precision, slits of the folding opening and the like are met after all the half ships are docked. The underwater folding method for the half ships effectively saves dock crane resources, is high in safety during the operation process, is simple and practical, and can be widely applied to various producing processes of large ships.