In the paper a numerical procedure developed in a Matlab® environment is presented, aiming at the definition of the main dimensions of a fleet of ships devoted to the transportation of a bulk cargo.

The procedure is meant to provide preliminary indication in the initial phase of feasibility studies.
The optimal dimensions are defined through a full factorial analysis. Relevant input data are information about the cargo to be transported (annual quantity, specific gravity, etc.), about the characteristics of the plants needed for cargo handling (weight, dimension, location on board) and about the route. The algorithm is based on a preliminary design modulus which provides solutions in line with requirements and preliminarily checked as regards basic trim and stability requirements.

The analysis includes, on the specific geometry considered, an evaluation of the seakeeping performances of the ship in the sea area covering the transportation route. The influence of adverse meteo-marine conditions reflects into an increase in the consumption and in a decrease in the average speed as compared with nominal values (in calm water). The inherent increase in running costs and the need for an incremented net weight nominal capacity to increase the probability of satisfying  the specifications in terms of annual actual transportation flow is accounted for.

A first set of results is presented, regarding a possible trade of Compressed Natural Gas in the North Sea area.