where, Hs is thc mean ridge sail hcight in meter, γ and δ are Weibull's paramcters that was determined using ridge sail height distribution function data Romanov and Gavrilo. γ and δ are given by equation (2.2.7) and (2.2.8) . 　 　 Ridge density (parameter 16-18) Ridge density D〔1/km] is obtained by equation (2.2.9). 　 　 where, T is hummock and ridge concentration in conventional units (1 to 5), Hs is mean ridge height (parameter 13). Mean, minimum and maximum ridge density are determined using equation(2.2.9) and observed hummock and ridge concentration data. 　 The envirnnmental data used for the voyage simulation The parameters required for the ship speed calculation code from WP6 were adopted in this simulation. The selected seven parameters are cold sum, mean first-year ice concentration, mean multi-year ice concentration, floe size, mean ice thickness, mean ridge size, and mean ridge density. The cold sum data were not used directly for this simulation. Those data are used to estimate the ice bending and compressive strength. As floe size, average value of 40 years was used. 　 2.2.3 Fulfillmnent of environmental data and interpolation of lacking data The reliability of the simulation depends on the fulfillment of the environmental data and the reliability increases with increase of the fulfillment rate. The yearly fulfillment rates of the data along the whole segments are shown in Table 2.2.5. Based on the data fulfillment analysis, the data were cut out or interpolated method as follows. 　 (1)As for cold sum, mean first year ice concentration, mean multi year ice concentration, mean ice thickness, floe size and mean ridge size, those data in which the data fulfillment mark lower than 50 percents are not used. Cut out data： N route 1953-56, 61-63, 72 S route 1953-56, 62-64, 72 　 (2)The data of the year in which the data fulfillment was from 50 to 100 percents are interpolated in the direction of segments or months. 　 In the case in which the data are lacked more than five consecutive segments in the direction of segments or months, the average data of about 40 years of the segment are used. As to ridge density the average data of 40 years of the segments are replaced for the lacked data, since the average of fulfillment is low as 27 percents.