Finnish-Swedish ice class rules require resistance estimation of ship navigation in a brash ice channel with a certain condition; channel width and thickness are specified in the rule. Some conditions such as size and shape distributions of ice pieces are not specified in the rule, but will affect a ship resistance; investigation of effect of these parameters is required to develop a more exact evaluation method of resistance values with experiments or with calculations. We investigate the effect of these conditions against ship resistance using a numerical estimation method we have developed based on physically-based modeling. We also develop a method to prepare a channel filled with ice pieces, which are placed randomly but do not penetrate each other. The channel resistance under irregular ice arrangements is compared with that under regular arrangements. Results of the numerical simulations show that arrangement of ice pieces and existence of a stopper block at the further end of the channel do not significantly affect the ship resistance. Effect of the number ratio of spherical and cubic ice pieces is also investigated; the more the spherical ice pieces are, the less the resistance is. This suggests that an appropriate ratio should be chosen, but the ratio is not obvious. Further investigations are required.
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