An approximate comparison is presented by Table 4.1-1 of the literal designations of ice classes between those employed by the Russian and other classification societies.
* A vessel belonging ice resistance category L1, or equivalent ice class used by other classification societies, may be permitted to travel, under the control of icebreakers, along sections of the Western area of the NSR up to 125｡?, and along individual sections of the Eastern area of the NSR during the summer navigation period, if navigation conditions are favorable.
* Icebreakers are permitted to navigate the NSR under ice conditions that correspond to the designation of their respective ice class. On a case-by-case basis, the Administration (Headquarters) may permit the operation of an icebreaker under more severe ice conditions than these envisaged by its ice class. Such permission would be granted following a review of the appropriate documentation, provided by the owner of the icebreaker, confirming that the state of the hull, machinery, and systems of the icebreaker satisfy navigational safety requirements in the NSR area and preclude the possibility of sea pollution.
* Class-L2 vessels may be permitted as an exception, upon special decision of the Administration (Headquarters), in the summer navigation period in the Western area of the NSR under favorable navigation conditions. Operation in ice of class-L2 vessels in the Eastern area of the NSR is not permitted.
Structure
* All vessels must have a double-bottom floor throughout the entire width of the vessel and over the entire length between the forepeak and afterpeak bulkheads. Tanks in the double bottom and double sides may not be used for storage of petroleum products or other harmful substances.
* The cargo tanks of tankers with deadweight greater than 5,000t used to transport petroleum products, as well as the cargo tanks of chemical carriers and gas carriers, must be situated at a distance of not less than 0.76m from the outer sheathing of the vessel hull. Tanks in the double-bottom floor and the double-sides of tankers may be used as tanks for isolated ballast, or must be kept empty.
* The hull of the vessels must have a shape appropriate for navigation in ice-covered waters. If hull shapes are different from these recommended by the Russian Rules, operation of such vessels on the NSR must be approved by the Administration. Bulbous bows are not accepted.
* Russian ships built before 1981 are subject to special inspection by the Administration.
* To ensure the possibility of close towing of the vessel by an icebreaker, additional supports to the sheathing and framing must be provided in the bow part of the vessel hull. It must also be possible to fasten a tow line to the tip of the bow. If necessary, devices should be provided for removal and stowing of anchors onboard the vessel (Figure 4.1-10).
Engine
* The time taken to reverse the main propulsion engine (in maneuver mode), or to switch the blades of the controllable-pitch propeller from full ahead to full astern, must not exceed 45 seconds.
* In reverse (full stern) operation, the main propulsion engines must provide at least 70% of the rate of revolution of the forward running mode.
* The propellers must have at least four blades and be made of stainless steel or high-strength bronze. Detachable blades are preferable.
