ABSTRACT
Figure 3 shows the ice-induced damage of a 1A ice class bulk carrier built in 1985, which has 4693 t DWT, a length of 91 m, a width of 16 m, propulsion power of 2600 kW and an average draught at incident of 5.95 m. The damage extended over the full webframe spacing of 2.8 m and three stiffener
1 INTRODUCTION
Ice-induced loads are known to have a strong stochastic nature due to the stochastic nature of ice strength properties and the ship-ice interaction process. As ice is formed in nature, numerous variables affect the mechanical and physical properties of ice. In addition ship operations in ice can have various forms: independent navigation or navigation with icebreaker assistance e.g. in level ice, ice floes and ridged ice with various amounts of firstyear and multi-year ice features. Furthermore, the physical process of ice breaking is not captured in all operative scenarios and ice conditions. Therefore, long-term full-scale measurements give the most reliable basis to evaluate the load level as a function of occurrence frequency (return period). Figure 1 shows an example of the long-term loads measured on-board MV Kemira during a 7-year period from 1985-1991. The transversely stiffened bulk carrier MS Kemira was built in 1980 to the highest Finnish-Swedish ice class 1A Super. In order to obtain these long-term loads MV Kemira was instrumented with shear strain gauges attached to the neutral axis of the frame where the difference between the two shear stresses on the same frame is proportional to the load on the frame between the gauges. The ship side-view and measurement locations are given in Figure 2, therefrom
spacings of 0.35 m resulting in a maximum deflection of 55 mm deforming the 15.5 mm thick plating and longitudinal HP profiles of the dimension HP200 × 11.5. The webframes of the dimension 600 × 10 have not been deformed significantly. Typical for ice-induced damages is the permanent deflection in the centimetre range experienced by the plating between frames, whereas the transverse frames have somewhat minor deformations.
