The authors previously discussed (SNAME Transaction 2013) the fallacies of the U.S. Navy modifying an existing "parent" or "legacy" design as opposed to a new "clean sheet of paper" design. We explained that many acquisition executives believe that a so-called "modified repeat" design has fewer technical risks than a new design. Yet, this approach has frequently resulted in significant cost and schedule growth and/or serious technical problems during construction, in-service and during modernization. The authors will describe why traditional design and build margins and Service-Life Allowances (SLAs) for weight/displacement, vertical center of gravity (VCG), electric power, and cooling are necessary but not sufficient because they can still result in ships that are "too little". The authors will stress the need to include and place more emphasis on space and volume and relate these to "just right" design requirements for reducing work content in detail design & construction and in-service modernization. On the other hand, some recent new designs have also experienced unanticipated cost and schedule growth during construction as well as substantial technical problems. The authors will examine some of these new ship designs and highlight the fallacies of over-constraining arrangements through arbitrary size and displacement restrictions – another example of "too little." We will emphasize that displacement is NOT a good indicator of cost – a lesson learned by leading foreign navies years ago. The authors will scrutinize the "too much" syndrome of incorporating unproven technology into a new ship design before it is demonstrated, or at least fully characterized and the ship impact understood. The cascading deleterious effect of including multiple major unproven technologies inevitably results in cost and schedule overruns. Indeed, one entire class of ships has been described as a "failure" due to "too much" new technology going into the design before its time. The authors will also briefly describe the development and use of more physics-based design tools during early stage design. This can reduce the risks of a new clean sheet ship design through early rigorous design space exploration and actual design maturation. The authors are convinced from our experience on over fifty major naval ship designs that much of the unbudgeted and unnecessary growth in the costs to produce naval ships can be attributed to poor design decisions made during early concept design. Achieving the "Goldilocks effect" of "just right" design starts with a mature stable ship design earlier in the design process. This is critical for ensuring successful ship design, acquisition, construction, in-service and modernization outcomes.

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