As mentioned above, the ship's speed under icebreaker escort is derived from the relation between ice index and ship speed of an escorting icebreaker. The horsepower of the three cargo ships in channels opened by a leading icebreaker was assumed to be 10% higher than in open water, and their fuel expenses were calculated on this basis.
Calculation of shipping cost
The index generally used to calculate operational costs is the freight rate. Freight rate is the sum of yearly average cost per ton of cargo and an anticipated profit per year. For example, the freight rate for cereal shipped to Japan from the Gulf of Mexico is expressed as 12US$/t. As a ship operational cost often varies considerably with season and year, if the ordinary approach is applied to operational cost estimation for the NSR, no definite data will be available for operational costs in each month and each route segment. It is assumed, therefore, that every voyage starts at the beginning of a month and the monthly costs are then calculated for a single voyage. On this monthly data basis, the freight rate is derived from the annual cost and a number of possible voyages. In the cost simulations, the freight rate does not include a profit margin. Full-load voyages are assumed in all cases. Cost evaluation is carried out in one of the two following ways.
Monthly voyage simulation
To examine trends in ship speed in each month and each route segment, the monthly costs for a single voyage were calculated. In each case, Yokohama was used as the starting point and Hamburg the destination, and the ship was assumed to leave port at the beginning of the month as stated above. In voyages of longer than one month, data of the following month was used, except data on ice conditions, which were taken from the month in which the ship left port for the sake of continuity. These single-voyage simulations based on monthly data for each year was named the monthly voyage simulation (MVS). In the regional routes, Dikson and Tiksi were used as the starting points. In these calculations, cost data (Table 4.4-5) provided on a yearly basis were divided into monthly or daily costs as appropriate. The computer program calculated the hours under way in each segment, which yielded the costs required in the segment (Figure 4.4-6).
Annual serial voyage simulation
The freight rate is usually calculated from the costs required over a specified period and the total transporting cargo volume as their ratio, usually on an annual basis. In these calculations, a serial voyage operation between Yokohama and Hamburg for a year was simulated, and the voyage started at Yokohama on January 1. The anchoring days at each port are selected from the actual operation data. At the end of the year, if the ship was in the middle of a journey, the time was extended until the ship reached port, and the equivalent number of voyages per year was calculated. When the month changed in the middle of a simulation, the data of the new month were used. This simulation was called the annual serial voyage simulation (ASVS). In selecting the optimum route for the voyage, which included alternative NSR routes as well as conventional routes via the Suez Canal in severe ice conditions, the final freight rate was deduced from the annual serial voyage simulation. A flow chart of the calculation program appears in Figure 4.4-7.
