An alternate method for the determination of aircraft carrier limiting displacement for strength

Abstract

Aircraft Carriers are currently exceeding design displacement limits, with minimal Service Life Allowance margin. Current aircraft carrier displacement limits are based primarily on structural strength criteria under very limited load and environment conditions. Traditional methods of determining hull girder displacement strength utilized an arbitrary safety factor of 15 percent which was allowed between the Calculated Primary Stress and the Design Primary Stress. The use of this safety factor and others has resulted in the establishment of a conservative displacement limit. This established displacement limit fails to provide an adequate margin of comfort for the addition of post construction weight to aircraft carrier hulls and does not provide an accurate indication of the actual hull girder displacement limit. A first failure analysis of fifteen sections of the newest aircraft carrier design (CVN 77) was conducted. The results of this analysis along with output data from the Ship Hull Characteristic Program (SHCP) were utilized in forming an alternate method for determining the limiting displacement for strength for aircraft carriers. Although the present aircraft carrier displacement limit takes into account numerous other limitations, this process deals only with the hull girder displacement limit for strength. This study does not provide a specific number for the displacement limit for strength for aircraft carriers; however, it does show that the NIMITZ aircraft carrier hull is potentially capable of sustaining significant additional weight without exceeding established Maximum Allowable Bending Moment limits.