The UPS system provides uninterrupted power supply to the critical equipment of the ship and consists of an UPS device and battery installed between the ship’s electric power network and the critical equipment. Normally, the UPS device is charged through the power network and in a black-out situation it will release the stored energy from the battery to the critical equipment.

This thesis presents the UPS-system that will be installed on M/S Wasa Express, its operating principle, operating requirements and dimensioning principle. The thesis also examines safety regulations related to the UPS- system and the operation of the hydraulic accumulator that is to be installed on the vessel. The purpose of this thesis is to familiarize with the UPS-system and ship’s electrical power production and examine the achieved benefits of the installation of system.

Due to the limited capacity of the UPS-system, the ship’s steering gears were excluded from the system, but their dependability is assured by installing hydraulic accumulators. These accumulators will secure the steering of the vessel in black out -situtation. This thesis presents the operating principle of the hydraulic accumulators and theory of selecting, dimensioning and installing the accumulators.

Improving the safety of the vessel is the main purpose of the thesis, and this will be achieved by installing the electric UPS-system and hydraulic accumulators. The thesis also evaluates other economical savings associated with the installation of the system, for example fuel and lubricating oil expenses and maintenance and overhauling costs of the auxiliary engines. The environmental friendliness of the vessel will be improved in the future by stopping the second auxiliary engine, which will reduce the emissions to the environment.