ABSTRACT The dynamic response of the Canmar Kigoriak to ramming multi year ice floes is determined from a three dimensional finite element representation of the hull and the surrounding fluid. Twelve ramming cases including three unsymmetric rams were analysed. Good agreement was obtained between calculated and measured flexural stresses at three longitudinal sections, for all cases examined. The comparison is less favourable for shearing stress distribution, particularly peak shears, though there is good agreement with the overall shearing forces at the measured sections. INTRODUCTION Recent theoretical investigations and field testing (Refs. 1 and 2) have indicated that the global ice forces generated when a vessel rams a sizeable ice floe may cause in addition to quasi static stresses, considerable cyclic stress amplitudes. It is important to quantify these dynamic effects, in order to establish appropriate sectional properties for vessels whose operational requirements include ice ramming. The relative merits of using sophisticated three dimensional finite element models as opposed to beam element idealizations to determine hull response to ramming forces has been the subject of topical interest. The Canadian Coast Guard Northern has recognized the need for further work in this area and contracted Canadian Marine Drilling Limited to examine this problem employing results from full scale impact tests data. Thework presented herein describes the development of one such detailed three dimensional dynamic model of the icebreaker hull structure and its hydrodynamic coupling to the surrounding fluid. The primary objective' of the work is to obtain a set of stress time histories at predetermined locations in the vessel for a number of symmetric and unsymmetric ramming cases, to enable a detailed comparison to be made with measured values and those obtained from a beam model (Ref. 2). References and illustrations at end of pap A super element approach has been used to model the entire hull structure and to provide three dimensional modelling of the surrounding fluid while the response of the structure to the impulsive loading is determined using the Method of Modal Superposition. FINITE ELEMENT IDEALIZATION The modelling requirement called for a detailed description of the hull structure and surrounding fluid in order to fully define the global response of the vessel to impulsive loading. At the same time interest was concentrated on specific instrumented parts of the structure to enable a detailed comparison to be made between the calculated and measured stress time histories at the locations of interest. There was thus no need to evaluate all of the element stresses throughout the course of each ram, indeed it would have been prohibitively costly, computer wise to have done so. Instead recourse was made to the general super element program SESAM 69 (Ref. 3) whose principal strength lay in its ability to utilize sizeable substructures or super elements to define the entire structure in an economical fashion.