Method and a control arrangement for controlling vibrations of a propulsion unit of a vessel

A control arrangement for controlling vibrations of a propulsion unit of a vessel, the propulsion unit comprising:

• a frame construction having an upper portion and a lower portion, the upper portion forming an outwards from a hull of the vessel protruding support arm, the lower portion forming a longitudinal compartment having a first end and a second opposite end,
• a propeller shaft being positioned within the lower portion of the frame construction,
• at least one propeller being attached to the propeller shaft,
• a first electric motor driving the propeller shaft,
• the control arrangement comprising:
• at least one measuring device for measuring vibrations of the propulsion unit,
• a first torque controller for producing a torque control signal to the first electric motor,
• a first additional torque controller receiving as an input signal measured vibrations from the at least one measuring device,
• a first active vibration controller for producing a first auxiliary torque control signal based on the measured vibration signals, whereby
• the first auxiliary torque control signal is added to a first torque control signal produced by the first torque controller of the first electric motor, the first auxiliary torque control signal acting against the measured vibrations in order to attenuate said vibrations.