There may be a lor of studies on the economic design of ship for the most favorable combination of design basis on the owner's request. However, there are few on the economical ship's size and speed for the ship owner's stand point. This paper describes on the optimal ship's size and speed to the given marine commercial environments for the owner's requirement to the shipyard. As the result of the paper, the criterion curve of bulk carrier will also be used to assess existing ships for their profitability.