| Résumé | The global ship impact forces on the CCGS Amundsen are quantified here for 44 impacts with multi-year ice floes in the Beaufort Sea. Global impact forces were derived from an inertial measurement system called MOTAN. In general, global forces of up to 9.0 MN were measured for maximum impact speed from 3.1 to 10.2 kt. Most of the impacts were conducted with two floes of known thickness and strength. Only two floes were sampled during the two-week program, but they characterized a wide spectrum of multi-year ice. Floe B1S1 was the thinner of the two floes (7.2 m), quite warm, saline and relatively weak (the depth-averaged borehole strength of the two test holes was 7.3 MPa and 4.5 MPa). Floe B1S2 was thicker (8.0 m), colder, less saline and stronger (the depth-averaged borehole strength of the uppermost 7 m of ice was 22.0 MPa). As anticipated, global impact forces and ship accelerations were higher during collisions with the thicker, stronger floe than the weaker floe, for comparable ship speeds. The highest surge acceleration (1.03 m/s²) occurred during the final ram with Floe B1S2 which was conducted at a maximum impact speed of 6.7 kt. That collision generated the highest global impact force of the program: 9.0 MN. The highest heave acceleration (0.84 m/s²) and sway acceleration (0.46 m/s²) occurred during rams with Floe B1S1, while transiting to a natural harbour within the floe. Global forces from 18 impacts with isolated multi-year floes floating in open pack ice were comparable to many of the rams with Floe B1S1, for a given impact speed. Comparison of the Commanding Officer’s expected ice severity for the 18 impacts indicated that even experienced personnel can have difficulty ascertaining the competency of multi-year ice. Impact forces and accelerations measured by MOTAN on the CCGS Amundsen were comparable to MOTAN-derived measurements on the CCGS Terry Fox from oblique impacts with bergy bits. The maximum heave, surge and sway accelerations on the CCGS Terry Fox were respectively 0.57 m/s², 0.56 m/s² and 1.24 m/s² during the Bergy Bit Trials, with measured global impact forces of up to 10.6 MN. Global impact forces and accelerations on the CCGS Amundsen during this study were not nearly as high as the impact forces measured by other instrumentation systems on ships operating more aggressively in Beaufort Sea multi-year ice. |
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