AbstractThe objective of this paper is to develop a computer‐aided optimal planning method for designing a marine heat and power generation plant which is composed of combining Diesel and turbogenerators, an exhaust gas economizer, auxiliary boilers and so forth. As there exist many alternative combinations concerning generators and boilers in constructing the abovementioned plant, it is important to determine the plant construction properly by selecting total numbers and scales of respective generators and boilers so as to optimize the long‐term economy of the plant.In this planning method, several design conditions are first set which are necessary for the planning of the objective plant, i.e. several patterns of ship's operational condition are set first, and both energy demands and steam output from an exhaust gas economizer are estimated for each pattern. Next, setting an alternative plant composed of combining generators and boilers adequately, the optimal operational policy for each pattern is determined by minimizing the fuel cost under several physical constraints based on linear and quadratic programming methods. Considering the results obtained above hierarchically, annual capital and operational costs of each plant are calculated, and the best plant construction is lastly determined by comparing the economy of all alternative plants.A numerical study has been carried out on a plant of a high speed container ship actually planned, and it is ascertained that to find the best construction of the plant the optimal planning method proposed here is advantageous compared with the conventional trial and error met