One of the most widely used methods for representing the shapes of ships and offshore plants is triangular mesh, which has a simple structure and is easy to visualize. In particular, lightweight models composed of triangular meshes are often used as a sharing medium for three-dimensional (3D) shape design results in the collaboration process among many stakeholders participating in the construction process. Currently, there are demands for visualizing the total shapes of ships or offshore plants for design review, interference check, construction monitoring, and securing maintenance space. However, this requires high computing power and much time due to the large size of the triangular mesh model. We have two general solutions as follows: simplifying the shape of the ship and offshore plant structure and reducing the size of the lightweight file itself. Between them, this study proposes a method for reducing the lightweight file. This method classifies the part types of the ship or offshore plant structure and then only stores the minimum triangular mesh information for each part type, excluding unnecessary information. Then, the topographic information of triangular meshes is stored together in the lightweight file to shorten the time required for restoration of the lightweight file.