for this simulation is set as 3knots. Fig.3.1.1 shows the relation between the mean ship speed and ice index of 25BC, 40BC, and 50BC. From the relationship, the Ice indexes to operations that need an escort of icebreakers (INC) are defined as -4, -4, and -1 to the cargo ship 25BC, 40BC, and 50BC respectively. If the ice index for a cargo ship in the route segment is more than INC, then a cargo ship can navigate independently (named Independent voyage mode). On the other hand, if the ice index is less than INC, it is supposed that the cargo ship cannot navigate independently and needs icebreaker support (named Escort mode).
It is assumed that an icebreaker can escort a cargo ship without any standby time at the starting point of the segment. In recent years, observation technology for sea ice including satellite has made remarkable progress, so it is plausible to predict the ice condition and to set up an icebreaker arrangement at the appropriate destination. The decision for terminating icebreaker escort is assumed. Even though a cargo ship can voyage in the segment next to the escort mode segment, it is realistic to make the judgement considering predictable ice condition at precedent segments. Accordingly, we assumed a cargo ship might have icebreakers, escort maximum for one day even if ice condition betters. About 10 knots of voyage speed is assumed as a proper average speed referring from WP5 report to the voyage speed of SA-15 class when she has escort by the Arktika-class icebreaker in the moderate ice condition. The simulation code search the existence of other escort mode segments among the next 12 segments (the distance of 240NM), when the voyage is judged to be independent mode from escort mode only by ice-index. If it finds any difficulty to make an independent voyage within the next 12 segments, the assistance of icebreakers is continued (named Watching Mode). When it does not find any problematic segment within the neat 12 segments, escort mode would be switched to independent mode at the next segment. Fig. 3.1.2 summarizes the decision of algorithms used to judge the mode. Also, Figure 3.1.3 shows the example of escort decision.
Assumption for ship speed and required engine power
Ship speed is estimated using the calculation model corresponding to three types of voyage modes (Independent voyage/ Escort / Watching). At an independent voyage mode segment, the ship speed distribution is estimated based on the relation between ice index and ship speed. The distribution of fuel consumption, which is necessary to calculate fuel cost, can be calculated based on fuel consumption rate, required power, and voyage time. In order to obtain the distribution of required power to the distribution of ship speed ; 1)speed-power curve at open water is referred when the ice concentration of the segment is zero, 2)speed - power Curve at ice covered water when the ice concentration is greater than zero respectively.
The distribution of navigation speed in the segment of escort mode or watching mode is coincident with the distribution of icebreaker speed. It is estimated using the relation between ice index and ship speed for icebreaker, A distribution of fuel consumption is estimated based on a fuel consumption rate and a required power in broken channel for a cargo ship and a navigation time. The power of cargo ship in broken cannel following the leading icebreaker is estimated as 10 % increase of one in open water, considering the friction and interaction of ice pieces.
Cost description methods
The following two ways of cost evaluation are attempted.
Monthly Voyage Simulation (MVS)
A ship operation cost may vary considerably by season and year. A cost required for one voyage is calculated as the first step to examine the trends for navigation days, icebreaker escort times and costs etc. In this calculation, it is assumed that voyages are always in a
