Pack ice as defined in the report indeed constitutes a certain percentage of ice types, but this definition implies relatively large ice floes but does not include so-called broken ice - smaller floes which broken and pushed away by ship, which are frequent over NSR in all seasons especially in summer-fall and which is more appropriate for simulating motion behind an icebreaker.
Narrow leads and fractures always exist in virtually any ice conditions. Although their areal concentration can be negligibly small, their importance may not be ignored since experienced navigators never miss a chance to take advantage of the leads/fractures by-passing severe ice and formidable features. As a result, the route-specific (i.e along the pach of ship) ice conditions are considerably easier than region-specific (average over a rigion) ice condition. Leads, fractures, polynyas and other openings contribute most into this difference. Although this difference was aknowledged in 2.6.4 this was done based on a wrong assumption that ice thickness and concenteration are the main factors in selecting an easier path. The main obstacles to by-pass are usually breccia fields, hammocked ice, embedded multi-year features and so on. And the main features to by-pass throughout are leads, fractures or cracks of any widths, and other openings. When the ship is wider than the fracture or crack, she is moving by further widening the fracture like in a too-narrow channel. Formulations for level ice resistance are not applicable for this mode. Resistanse in broken ice and in widening a channel has been well described by Ryvlin and Kashtelyan (see e.g. Ryvlin & Kheisin. Tests of Ships in Ice).
5. Section 2.7. It is unclear why legal assessments are based on an L2 ice class vessels and what correction should be made to ajust it to L1 or higher ice classes.
6. Tables 4.1.2 and 4.1.3. It looks amazing that the freight cost in October is less than that in September.
