This paper deals with the mechanism associated with dents of ship hull plate caused by ice block contact. Authors carried out experimental researches on dents and tried to clear the mechanism of it. In these experiments, an ice block fixed in a open rigid box was pressed repeatedly against a model hull panel. By means of changing the box shape, they could obtain a variety of constraint degree relating toke block deformation. Test results were compared with full scale data and those of calculation.
For ice-going ordinary ships, it is not rare that various dents are experienced on the hull. The navigation period of icebreaker is longer and ice condition is severer than those of other ships, so the circumstances are same for icebreakers. Appearance of modern powerful icebreaker accelerate the seriousness of problem. As the power of icebreaker grows higher, the dent damages occur more often. Some reports say that damage due to bent, buckling or indent of bottom plates reaches78% of all damages of icebreakers which were necessary to be repaired. The mechanism of dents is an important problem to be solved for the safety of ships. Figure 1shows the flow chart of investigations in order to know the mechanism of dent occurrence. It is important for us to dear black boxes in this chart, so we should use every known information in known boxes and make some assumptions. As mentioned figure I, in the present state of affairs, we can understand little part on the mechanism of dents. We can give some reasons for it as follows: First, because of variety of ice condition we cannot decide what condition causes this damage. Second, as the problem is the interaction between ice and ship's hull, the mechanism is so complicated.