7.30 thus introduced would tend to make results more rather than less conservative. The analysis of this section will proceed to develop an equation relating the thickness of the inner hull, the outer hull, and the bulkheads to the stress developed in the bulkheads. If thicknesses are determined for the inner and outer hulls, they may then be used for form a relation between the bulkhead thickness and applied stress level. Finally, the bulkhead thickness thus obtained may be compared to that originally assumed in Sections VII.4.3.1 and VII.4.4 to see whether the original approximation held any validity. In order to begin the current analysis, recall that the bulkheads are subject to stresses due to differential expansion of the outer and inner hulls. The stress arising from this interaction has a circumferential as well as a radial component. This is the normal loading condition for a bulkhead section. In addition to these stresses, a plate bending stress arising from the pressure load must be imposed upon the bulkhead in the event of a failure in the outer hull (Section VII.2.4, Figure 7.2). VII.4.5.1: Calculation of the Normal Interaction Stress - Bulkhead Thickness Relation: Since the mechanism of the hullbulkhead interaction is of major interest to the designer and is less easy to describe concisely than those procedures used in Sections VII.4.3 and VII.4.4, a complete derivation is presented here rather than being referred to an appendix. Note the free body diagram of Figure 7.10. The following analysis deals with radial component of the bulkhead stress and is strictly valid for only those bulkheads in the cylindrical section of the hull. In addition to those quantities defined on Figure 7.10 two new parameters will now be defined, P 1 and P 2 . These are related to P 1 and P 2 differing only in that the average contribution of the bulkhead radial force Pb is now included in the determination of total force per unit hull area. The total contribution of the bulkhead radial force to the hull loading is given by the sum of the contributions of the longitudinal and transverse bulkheads:
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