During the manoeuvre of the ship's berthing at the quay an impact may occur and the resulting emission of energy in the system vessel - fender device - quay. Exceeding the permissible energy value causes damage to one of these elements and results in an accident. During the manoeuvre part the vessel's kinetic energy is converted into the vessel's turning in relation to the contact point with the quay. The article analyses the effective mooring energy absorbed by the fender device in the aspect of loss of part of the vessel's energy during turning. The relationship between the vessel's turing radius and the hull curve has been presentes.