The committee for the Safety of Japanese Nuclear Powered Merchant Vessel is now investigating the theoretical and practical basis of subdivision and stability rules for nuclear powered ships which comply with the recommendation of SOLAS 1960. At the investigation of damaged stability of nuclear powered cargo vessels, loss of GM after flooding at midship part was calculated for many ordinal cargo ships by Prof. Mandelli's approximate method. However, it seemed rather difficult to arrange these obtained data in forms suitable for explaining how the loss of GM is governed by hull form and ship condition. The author prepared this paper to solve the said difficulty. In the paper he transformed the formula for GM loss provided by Prof. Mandelli into a none dimensional form, and found that the loss of GM is mainly governed by breadth-draft ratio before damage and by damaged length. And the author presented a chart from which we can approximately but easily and quickly estimate the loss of GM after flooding at midship part for cargo ship with ordinary hull forms.
