Examination of the patterns of ship traffic in public ports of Central America and Ecuador reveals that ships arrive at random and in close agreement with distribution patterns predicted mathematically by the Poisson distribution. Pursuing the premise that it is the function of a seaport to transfer cargo between land carriers and sea carriers at minimum total cost, and based on the randomness of ship traffic, the electronic computer has been used to determine the most economical number of berths for a seaport under various different conditions of ships in port, idle port facilities costs, and idle ship costs. Tables and graphs are provided that are intended to facilitate the mechanics of the port planning procedure and to assist management in making sound decisions concerning seaport development.