The paper addresses methods used to analyse full scale trials for performance determination of ships in ice. Furthermore uncertainties resulting from assumptions taken in the early stage when ice model tests are typically performed are discussed. In a first step the difference between model test based prediction and final determined performance from ice trial are shown for an example ship for which both results are available. The main assumptions are critically reviewed and possible reasons for deviations between the prediction and final outcome of ice trials are systematically assessed. The performance of ships in ice determined by model testing based on single combinations of speed and ice thickness is compared to full scale trial results. Furthermore the effect of generalizing impact friction and snow cover which is usually generalized for the model based prediction is determined by different methods. Finally a comparison between the propeller-ice interaction based on model tests and full scale trials is made to assess possible sources and magnitude of deviations between the performance prediction in early design stage and the final trial results.

The paper shows that even though the prediction of icebreaking resistance by theoretic means and by model testing is well established comparisons between performance results obtained from ice trials sometimes deviate in their values and trends from those predictions. Besides testing uncertainties also missing parameters and testing methods can be identified as reasons for differences in the results. Recorded time series of propeller ice interaction in full scale and model scale are compared and analyzed. Different scaling approaches are applied to the model scale torque trends and compared to the full scale data. The results of the comparison between full scale and model test results show the limits of the current methods and encourage to take a closer look at additional parameters with stronger influence on ice performance. Additionally the comparisons of ship performance and propeller ice interaction of model and full scale data will improve the understanding of the transferability from model to full scale data.

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