Initial Deflection of Hull

Abstract

It is well known that sagging deflections are induced at full loaded condition in aft engine ships, such as tankers. These sagging deflections cause the loss of dead weight even though there might be no trouble of ship strength. One of the factors inducing these sagging deflections may be considered the shrinkage caused by welding of block butts in constructing a ship on building berth. We call the deflection induced by this welding shrinkage "initial deflection". We investigated the initial deflections comparing actually measured deflection with theoretically calculated one for about twenty ships and found the initial deflections could approximately be represented by the following expression; δ=0.75L/Dn-77 (mm) where, δ=initial deflection L=length of ship D=depth of ship n=number of block butts To eliminate the initial sagging deflection, we decided to construct a ship in intentional hogging form equal to initial sagging deflection at the stage of ship construction on building berth. We have actually provided about twenty ships with intentional hogging deflections and obtained good results without any trouble.