Abstract
For Small ships with large hatch openings, we have studied the deformations of the hatch openings and the effects of longitudinal and transverse members on the deformations. In this paper, developing these researches for larger ships with large hatch openings such as having the side stringers or second decks, we attempt to have optimum structures by changing the flexural rigidities so that maximum bending stresses in longitudinal and transverse members are equal to a allowable stress. For a ship having large hatch opening (No. 2 hold is consisted of single deck system with side stringers, No. 2 hold consisted of second deck system), optimum ship structures are determined on the consideration of the maximum bending stresses in each member being equal to the allowable stress (10kg/mm^2 or 12kg/mm^2). From these studies the following results are obtained. (a) The scantlings of transverse members such as deck beams, side web frames between upper deck and second deck, and bottom floors are too large, but those of longitudinal bottom girders is insufficient. Therefore, the scantlings of these transverse members should be decreased, and the bottom girders should be reinforced by the saved steel weight due to reduction of scantlings of these transverse members. (b) If scantlings of bottom girders are increased, these of bottom floors can be decreased by the reinforcement of bottom girders. (c) Since the bending moment of bilge in second deck system is larger than that in single deck system by second deck loads, the scantlings of side web frames connecting to bottom floors in second deck system should be enlarged than those in single deck system.
