As a part of the ongoing move by many U.S. shipyards to adopt zone-oriented ship production, the need for an accuracy control system has been identified. Recent research has indicated that the accuracy control system can form the basis for performing process analyses as a means of improving productivity. This paper reports the results of Maritime Administration-sponsored research to develop a set of variation-merging equations for a specific vessel construction project. The equations are presented for the stern section (block 6) of the U.S. Navy T-AGOS ocean surveillance vessels under construction at Tacoma Boatbuilding Company. Data collected in 1982 provided process means and standard deviations for the following stages of production: part fabrication, panel line, subassembly and subblock assembly. Based on these data and observed assembly sequences, variation-merging equations are written and analyzed for the assembly of subblocks 602 and 603 and for the assembly of block 6 (that is, joining of 602 and 603). The impact on the merged variation of altering the assembly sequence is also analyzed and reported. The analysis is used to predict rework type (gas cutting or back-strip welding), and probabilities. Although these equations are dependent on the shipyard and the design, the techniques and principles for their development are applicable for any shipyard and any design. As such, they form a case study which makes them suitable as a guide for shipyards undertaking analysis of assembly procedures using variation-merging equations.

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