An approximate method for calculating the mean statistical service speed of container ships on a given shipping line and its application in preliminary design

During ship design, service speed is one of the crucial parameters in determining the operational economy of the vessel. As sufficiently exact calculation methods applicable to preliminary design stage are lacking, the so-called contract speed, the speed which a ship reaches in calm water, is usually cited. Żelazny (2015) developed a parametric method for calculating total ship resistance under actual weather conditions (wind, waves, sea current). This paper presents a parametric model of a ship’s propulsion system (screw propeller – propulsion engine) as well as a method, based on both the resistance and propulsion system models, of calculating the mean statistical value of a ship’s service speed under the seasonal weather conditions occurring on shipping lines. The method makes use only of basic design parameters, and may be applied in preliminary design phase of container ships.