Vibration levels in marine propulsion units can be extreme and the mechanical seals needs to be designed to handle these. A customer had end-users facing extensive wear of seal parts and as such premature failure occurred. The application was analysed with regards to vibration levels and frequencies which in turn was forming a part of the design criteria for the new design. Before being put in use, the performance of the new design was verified on a shaking table ensuring the capability of the design in the application having no coinciding of the excited frequencies and the natural frequency of the mechanical seal.