CASPPR's ice numeral is calibrated so that a value of zero corresponds to ice navigation at a speed of 3 knots. If the ice numeral becomes negative, the waters are judged hazardous for navigation. The relation between the ice numerals and the ship speeds obtained from the experimental voyage of the Kandalaksha reveals that, despite some variance, the ice numeral is a good predictor of ship speed (Figure 4.4-3; Yamaguchi, H., 1995). In this simulation, CASPPR's ice numeral was modified to include the influences of flexural and compression strengths of ice, ridge size and ridge distribution. To distinguish this numeral from the Canadian numeral, the numeral was named "ice index". The ice index is calculated by
I = IA + IB + IC
Where
IA = Basic ice parameter of ice thickness, ice age, and ice concentration
IB = Ridge parameter of ridge sail height and ridge density
IC = Strength parameter of flexural and compression strengths of ice
Figure 4.4-3 Correlation between ship speed and ice numeral obtained by the full-scale tests with the Kandalaksha
Normally the correlation between the ice numeral and ship speed is gleaned from operational data. Since no data is available for ships in the conceptual design stage, the correlations between the ice indexes and the three types of ship in the simulation were derived theoretically. In these calculations, a code developed in the ISNROP called NEWSIM2 (WP-155) was used to determine ship speed under various ice conditions. Loss of ship speed should be expected due to the presence of ice in waters adjacent to the official Russian NSR, such as the Barents Sea and parts of the Bering Sea. Because data from these waters were not included in the data set provided by AARI, the ice conditions were estimated from NSR data from adjacent waters, in which ship speeds had been obtained. In open waters, a uniform speed was assumed to be attained as shown in Table 4.4-4.
Figure 4.4-4 shows an example of the calculation for 50BC. Because the possible ice conditions corresponding to each ice index are numerous, a range of ship speeds is given for each ice index. The discrete probability distribution of the ship speed corresponding to every two pitches of ice index was then developed as shown in the figure, where the ship speed probability distribution for a certain ice index was indicated in five speed-levels. Once the relation between ice index and speed is known, the distribution of ship speeds can be easily determined following a flow chart as shown in Figure 4.4-5, where the data were utilized for a given year and month in each 20NM segment of the route.
