Icebreaking ships encounter various ice environments during their operations. So, in order to keep their navigating schedules, it is very important item to estimate ship performances and to evaluate the ability to transit the given sea route at ship design stage. At ISOPE 1994 in Osaka, the author presented a paper on the ridge transit performance of the icebreaking tanker and discussed the effects of ridge field on the transit ability.(Nozawa,1994) In this paper, using the same model ship, an practical estimation method of ship resistance in broken ice sea is reviewed and discussed based on classical theories by Kashitljan et al. and Enkvist.
Icebreaking merchant ships, observation ships and oceanographic ships transiting the ice sea, encounter various ice environments, namely, level ice, broken ice, ridge ice and open water. As for ship resistances in the level ice and ridge ice, many researchers studied and published their results. But there seems to be a few paper about the resistance in broken ice sea. It is important to make an estimating method of the resistance in broken ice sea for transit simulation as well as in the level ice because icebreaking ships frequently encounter the broken ice field and the ice covered channel broken by the icebreakers. This is the main purpose to present this paper. According to the sea ice nomenclature by World Meteorological Organization, the definition of concentrating of ice (hereinafter abbreviated as "CT":ice coverage,0.1–1.0) is as follows. Compact ice(10/10), very close ice(9/10–10/10), close ice(7/10- 8/10), open ice(4/10–6/10), very open ice(1/10–3/10), open water. Not only" concentrating of ice" but also "extent of ice "relates to the ice resistance. The broken ice size treated in this paper is supposed considerably small (the size is about 20–30m or broken ice by icebreaker).