For floe size, the mean values were used. As for the ship category, the cargo vessels were assumed to be classified as Type A and the Arktika type escort icebreaker was assumed to be classified as CAC1. Navigation under conditions of high ice concentration often suffers from ice pressure caused by winds and currents. In such cases, the ship incurs a great loss in speed and may be in danger of besetting. As the predominant impact of the ice pressure effect is on the parallel body of the ship, a correction factor for this effect to the ice index, CCO,, was introduced according to the length of the parallel body. The factor CCO is shown in Table C-5. When navigating ice-covered waters, ship masters tend to avoid severe ice areas and try to find open leads. This routing effect should also be taken into account in the ice index. Routing decisions will be made depending on the conditions of ice thickness and concentration. The correction factor for routing effect, Cma was then introduced, as shown in Table C-6. As the higher the ice concentration, the greater the difficulty in changing ship course, a greater penalty was assumed for higher ice concentrations. Ship speeds were arranged in a two-rank ice index. Since ship speeds corresponding to arbitrary ice index rank were distributed among a range of speeds, the variations were arranged in five ranks in terms of probability distribution. Results for three ship types and the Arktika appear in Figure C-6. Because a single ice index may correspond to several ice conditions, ship speed was derived from a distribution of a certain range of ship speeds corresponding to an ice index rank.
