Ship's hull under construction undergoes various deformations, such as bending up and down or athwartships and shrinkage fore and aft. The major elements to cause such a deformation are (1) loading (hull weight and water weight), (2) temperature variation, and (3) shrinkage force due to welding. The deformation of ship's hull is complicated, because the above elements affect the ship simu ltaneously and the intensity of element itself varies with time. Thus, while the length of ship, for instance, varies every moment with atmospheric temperature and sun shine, it tends to be shortened as a whole due to the welding shrinkage force. Furthermore, because of the nature of wood, the ship's bottom lying on wooden blocks lowers with time even if the load be kept constant. The present paper is concerned with the result of deformation measurement on actual ships, theoretical investigation, and practictal applications in ship-building in connection with, for example, the hull supporting method on berth and the method to find the most favourable propeller shaft center line.