Simulation-based design and virtual manufacturing based on 3-D digital mockup is an evolving technology that is widely used in mass production industries. The use of this technology facilitates design and production optimization by selecting from several potential design options and production strategies. This paper presents an effective usage of 3-D digital mockup systems for ship hull structures focusing on work strategy planning/evaluation. The newly developed system enables visualization and simulation of process planning for hull blocks, as well as interference checks in assembly stage and evaluation of production stage workability. A converter has also been developed to integrate data from CAD systems into commercial visualization/simulation software. The system has been applied to the production design of actual ships, and several useful lessons have been learned.