Weight Comparison of Ring- vs Ring/Stringer-Stiffened Cylindrical Pressure Hulls

Optimum ring-stiffened cylindrical pressure hulls have slightly lower structural efficiency than optimum ring/stringer-stiffened cylindrical pressure hulls for a constant ocean collapse depth. However, efficiency is achieved in ring/stringer-stiffened hulls with thinner walls which result in significantly higher wall stresses. Example steel and titanium hull designs are presented for collapse depths ranging from 2000 to 7000 ft. Titanium is superior in elastically stressed designs but alloys in either steel or titanium with sufficiently high yield strengths after welding are not available to develop the maximum potential structural efficiency of either configuration at deeper depths. A nondimensional structural optimization analysis which considers the several possible modes of instability and recognizes a number of practical design restraints (for example, a maximum ring/stringer height) is used to obtain these results.