Examination of Service and Stress Data of Three Ships for Development of Hull Girder Load Criteria

Book excerpt: This is a follow-on project to SSC-240, 'Load Criteria for Ship Stuctural Design', which proposed methods for the estimation and superposition of the primary loads and performed sample calculations for one conventional dry cargo ship. It involved the following bending moments: still-water due to weight and buoyancy; ships own wave train; quasi-static wave-induced, vertical and lateral combined; dynamic loads, including slamming, whipping and springings; and thermal effects. Here the service and full-scale stress data of three larger and/or faster ships (Containership SL-7, Bulk Carrier FOTINI-L and very large Crude Carrier UNIVERSE IRELAND) are examined for the purpose of the enventual development of hull-girder criteria. The examination is limited to extreme midship bending moment loads which are related to the ultimate strength. An assessment is made of the compatibility between the service and stress data of the distinctly different study ships and the analysis methods of SSC-240 and their assumptions for cargo ship type. Considerable insight is obtained into the probable correct mathematical approximations of the loads and their interrelationships. It appears that still-water bending moments can be approached probabilistically, however, considerable additional information on experienced loading conditions must be gathered to determine the statistical distributions. Additional effort is required to determine the suitable probabilistic expression and a synthesis method for the contribution of vibration to the extreme load. (Author).