This paper describes a prediction method for the contribution of the main onboard machinery to the underwater acoustic signature of steel surface vessels that can be used during the design stage. There are two reasons for the development of this method. Firstly, a small acoustic signature is important for naval and research vessels, due to operational requirements concerning detection and interference with acoustic equipment. Furthermore, anthropogenic noise underwater is an issue that receives increasing attention from the international community. This is due to the increase of underwater ambient sound levels over the last decades and concerns about the impact on marine life. The method uses Statistical Energy Analysis to model the vibration levels on the hull, using a simplified representation of the vessel. These levels are converted into the source level of the vessel using the radiation efficiency. The method is validated with measurements. The simplification of the vessel is shown to perform well, compared to a complete model for the underwater acoustic signature. The output of the method shows resemblance to measurement values for frequencies of 200 Hz and up, but further validation is necessary to incorporate the method in the design process.