Abstract: This paper deals with the ultimate strength and reliability of high-speed ships built in composite materials. The Johnson's beam-column formula is extended to estimate the load-capacity of the top-hat stiffened panel. ‘Failure’ occurs when the total impact bending moment of the ship exceeds ultimate strength of the top-hat stiffened panel at deck or bottom. The reliability and the uncertainty effects in design variables are quantified by an effective response surface method. Some conclusions are drawn, which can be referred to in high-speed ship design and further study.