Purpose of this thesis is to give an idea of the real facts and factors that have lead to real life choices in propulsion solutions. Development in technical field has created a wide range of alternative solutions for propulsion systems. Manufacturers offering these solutions often try to prove their application's financal and technical superiority by mathematical calculations. If these calculations are true, then there must be other hidden factors behind the decisions of remaining often with very conservative solutions. To find these hidden factors was the thing that inspired me in this thesis. Material sources for this thesis are mainly gathered from interviewing people from ship yards and shipping companies as well as propulsion manufacturers. In discussions I have used arguments from the opposition, and have tried to find answers to these. For information and reference different test results and marketing material from manufacturers as well independent sources have being used. Many document's shown or subjects being told cannot be directly published here due to information security. However, all this has given me a good insight into the facts and factors leading into the various outcomes in building projects.