SummaryThe assessment of hydrodynamic characteristics of a screw propeller in open water test is of crucial significance in the preliminary design stage of a ship. The open water characteristics can be accurately predicted by towing tank measurements. Taking into account the significant advances in computational fluid dynamics which has enabled the numerical assessment of the open water characteristics, the time and the cost of propeller design are significantly reduced. Open water characteristics can be assessed numerically using potential and viscous flow theory. The former one allows faster and simpler preliminary determination of open water characteristics. Within this paper, numerical simulations are performed for Gawn series propellers utilizing open source code OpenProp based on the moderately loaded lifting line theory and commercial software package STAR-CCM+ based on viscous flow theory. The latter one is more time consuming regarding the time required for the preparation of simulation as well as computational time. The obtained numerical results are compared with regression polynomials based on the experimental data. The validation of the results has pointed out that OpenProp can be used as practical and efficient tool in preliminary design of screw propellers.