IAis a basic ice parameter depending on age, thickness and concentration of ice. IB is a ridge parameter, defined by sail height and ridge density. IC is an ice strength parameter, which is a function of flexural strength and compressive strength of ice, to be estimated by cold sum.
Calculation of ice index
The calculation procedure of IA is almost the same as the Canadian ice numeral. The ice multipliers given by the CASPPR for CAC4 and Type A were revised, as shown in Table C-2, which lists the various types of first-year ice and their definitions, along with the ice multipliers for each ice type and ship category. The formula for calculation of the ice index is as follows, using the ice multipliers for first-year ice and multi-year ice given in Table C-2, where Cf is concentration of first-year ice and Cm is concentration of multi-year ice.
IA＝(corresponding ice multiplier for first-year ice)×Cf＋(corresponding ice multiplier for multi-year ice)×Cm＋2×(10−Cf−Cm) (1)
Ridge parameter IB can be obtained as following. Cr is defined as an index from 1 to 10 of ridge concentration, where the ridge profile is assumed as shown in Figure C-5. Ridge concentration as defined in the environmental parameter 16 is designated by Dr, and Cr is defined according to formula (2).
Cr＝Wk×(Dr/1000)×10 (2)
If ridge width Wk is approximated by Wk＝20Hs,
Cr＝(Hs Dr)/5 (3)
IB approximates according to formula (4).
IB＝F(Cr)×(Cf＋Cm) (4)
Where F(Cr)＝-2×(Cr/10)
In CASPPR's reckoning, if an area is 1/3 covered by ice ridges and ice concentration (Cf＋Cm) is 6 or over, 1 is subtracted from the ice multipliers in Table C-2. If the area is fully occupied by ridges, i.e. Cr ＝10, the formula (4) will give IB value twice as high as CASPPR's one.
Ic, an index of ice strength, is defined according to Table C-3 and formula (5). The lower the air temperature, the greater the penalty and the higher penalty for multi-year ice is counted.
