In any ship propulsion system the propeller performs the essential function: transformation of torque, produced by the prime mover, into thrust force. Marine propeller, as an essential part of the ship propulsion system, is the essential component from the functional point of view. The propeller becomes an important safety ship component in case of storm and heavy weather. For this reason all of the world wide recognized marine classification societies gathered in the International Association of Classification Societies (IACS), prescribe the requirements for minimal propeller blade thickness from strength point of view and the procedure for its calculation in their Classification Rules and Guidelines. Each society has it own approach, where all of them are modelling the same physical phenomenon: ship propeller in water stream. The aim of this thesis is to compare the propeller calculation procedures by various IACS calculation societies, focusing on their results validated on a few selected propellers that have been proven in practice, to find out in what amount the different classification societies procedures really provide different calculation results for the thickness of propeller blades. The thesis shows that, though modelling the same physical system, calculations of required blade thickness in order to meet the stress criteria in accordance with various IACS classification societies give significantly different results.