Currently, fishing boats engaged in fishing activities off the coast of Korea are mostly made of FRP; furthermore, in consideration of the environmental protection, they are also being fabricated from recyclable aluminum. Presently, domestic aluminum coastal fishing boats are constructed after obtaining approvals from the Korea Maritime Transportation Safety Authority and Ministry of Oceans and Fisheries. For aluminum coastal fishing boats, tonnage regulations are observed depending on the size of the hull and house, and the shape is defined accordingly. This plays an important role in the initial ship owner's requirements, as the ship is built, and the ship structure can be defined by calculating the thickness that satisfies the regulations, based on the projected load on the structure. Herein, a design method and guideline for a 9.77-ton catamaran aluminum fishing boat that can utilize the deck area optimally in relation to the fishing utilization area are presented. Although existing research data are applied to the design and structure of small and medium-sized vessels for safety, in this study, design loads are applied by considering the structural shape of the fishing boat, and a joint strength analysis is performed to secure the safety of the vessel.