The Deformation of Ship's Hull under Construction (No. 5)

Abstract

In this report, three subjects will be dealt with. First, an example of variation of transverse shrinkage of ship's bottom plating during progress of hull welding will be illustrated, which variation of shrinkage somewhat resembles that found in fore & aft direction.Secondly, an attempt will be made to explain results observed in actual cases of ship construcition which indicated that the ship's bottom deformation such as the rising of the stern was caused chiefly by welding the bottom in the vicinity of the deformation and was little affected by welding of the main deck & structures above the main deck.The third and major discussion will concern the influence of ship's deformation on the propulsion shafting. When main propulsion shaft bearings are out of line, many troubles should be anticipated, such as shaft failure, extraordinary wear-down of bush or bearings, vibration or whirling, and loss of power etc.Regarding the problem of untrue shaft bearing, the variation of bearing reactions and the bending moments in shafting corresponding to various alignment conditions were calculated on one ship. The comparison of the resulting calculations led to the conclusion that the most important thing is to equalize the bearing reaction and bending moment of shafting everywhere as much as possible. It is only of secondary importance to maintain all bearings on straight line.Another conclusion resulting from the calculation is that a faired deflection of bearing position such as deformation due to ship's hogging or sagging, even if the amount of deviation of bearing position from a reference line is remarkably large, will do little harm the shafting. Rugged deformation such as in case of stern bush wear-down or local deformation due to welding will be harmful to the shafting.