Since this speed is considered the critical speed at which a ship could usefully operate, the regulations define that at ice numerals less than 0 the ship is considered to be navigating dangerous waters. In the experimental voyage, however, the Kandalaksha delivered speeds of 4-9 knots at an ice numeral of 0, indicating that the Canadian ice numeral is set more conservatively (with a higher safety margin) than anticipated. For summer navigation in the presence of melted ice, CASPPR would normally correct its formula for calculating the ice numeral. The Kandalaksha's results suggest that a greater correction for the ice numeral may be possible.
[9] The tactical diameter in ice concentration of 4-6 was roughly the same as in open water (Figure 5.13). However, in more severe ice conditions the ship was unable to manage a 360｡?urn.
[10] As a rule, measurements were conducted at three-hour intervals of natural conditions such as meteorological, hydrological and ice conditions as well as salinity of the surface water. Variations in salinity along the route are shown in Figure 5.14. Salinity along the coast from the Sea of Okhotsk to the Bering Sea is approximately 3.2%, a value in the normal range, but upon entering the Chukchi Sea salinity values dropped precipitously, falling to a low of 0.2% in the East Siberian Sea. The causes of this phenomenon are thought to be melting of ice and especially the inflow of fresh water from the rivers of the mainland. In some locations, particularly the boundary between the Chukchi Sea and East Siberian Sea, sudden changes in salinity are observed, where turbulent vortices are generated by the complex interactions of river flows and ocean currents.
While the ship followed a course further offshore, salinity again rose and became much more uniform. Each sea has its characteristic sea surface temperature and salinity. Water masses in these seas can thus be divided clearly in the T-S diagram (Figure 5.15).
