The purpose of this report is to set forth data and practices for determining the performance of marine diesel power plants. This report is applicable to low or medium speed diesel of the two or four-cycle naturally aspirated or turbocharged types. It is intended that this guide be used for evaluating the performance of diesel propelled ships as compared with those propelled by steam or gas turbines. In order to simplify and standardize these evaluations, the ambient condition selected, the heat content of heavy fuel and other allowances used are the same as in the SNAME Technical and Research Bulletin 3-11 "Marine Steam Power Plant Heat Balance Practices". This report includes methods for comparing diesel performances when burning light, medium, and heavy fuel oil, as well as methods for determining performance when the ambient conditions are other than those selected as standard. Every effort has been made to keep this report as reasonable and fair as possible and close to the general practice of the industry, without curtailing individual initiative, When in the development of a design, specific data for a particular application becomes available, these data should be used in preference to the data given herein. Throughout this Bulletin, reference is frequently made to the SNAME Technical and Research Bulletin 3-11, "Marine Steam Power Plant Heat Balance Practices", where data on steam auxiliaries are required. ½ here referenced, it is referred to as T & R 3-11.