This thesis points out the complexity of the design of small craft propulsion system, detection of errors and their correction. Within the technical description it can be found all the necessary data and details regarding the selection of equipment and engine auxiliary systems and a description of the selected system. With the propulsion engine there are the propeller shaft, propeller, sea and cooling water systems lubricating oil system, exhaust gas system. This work points out the theoretical part tied to four-stroke diesel engines. It describes the basis on which they are incurred, their development and implementation, all supported by examples and illustrations. Engine marinization is an adaptation of engines for salt or sweet water conditions which is common in marine engineering. For quality marinization, it is necessary to follow the rules and to give the utmost attention to the installation of the cooling system. It is possible to achieve good result with high quality installation. When modelling engine in commercial program the problems you may encounter are evident. After modelling graphs, that describe the current state of the engine, fuel composition, pressure, temperature, mass flow and other parameters, are displayed. This researchincludes the heat exchanger calculation and the schemes of the system.