* When a convoy is formed of ships with equivalent icebreaking capability but different widths, the commercial vessels are arranged in descending order of width, with the widest ships at the front and the narrowest at the rear.
* The worse the ice conditions are, the smaller the number of escorted ships is and the smaller the distance is between ships.
* If any of the ships in the convoy is prevented by the ice from moving forward, the icebreaker frees that ship by passing on the side of the ship.
* During the operation described above, great care must be taken to the ship-to-ship interactions between the icebreaker and the distressed ship.
* Similarly, in the same situation, when the icebreaker moves at low speed, a hazard of damage exists to the hull, propulsion system, rudder etc. of the distressed ship, due to ice blocks in the water between the two ships.
Under extreme ice conditions, particularly when wind or tides cause pressure to form in the ice, the channel created by the escorting icebreaker may close up before the escorted ship has time to pass through, curtailing the speed of the vessel and causing frequent stoppages. In these cases the escorting icebreaker may be obliged to tow the escorted ship. Although this towing is sometimes performed using a cable, under extremely harsh ice conditions a method developed uniquely by Russia is used, known as close-towing or fork-towing (Figure 4.1-9). In close-towing, the icebreaker tows the escorted ship with its bow attached directly to a notch in the icebreaker, called the stern notch (Figure 4.1-10). According to data regarding the towing of an SA-15 commercial ship by the nuclear icebreaker Arktika through 160-200cm first-year ice, the convoy was able to muster a speed of only two knots without towing, but was able to improve this speed to four knots using close-towing - the same as the Arktika's speed when navigating alone (WP-107). When the escorted ship's displacement exceeds that of the escorting ship, the escorting ship is known by experience to suffer a decrease in maneuverability. The largest ship that an Arktika-class nuclear icebreaker can escort using close-towing is the S-15 class ship with displacement of roughly 25,000t.
When navigating in ice-covered waters by convoy, especially when using close-towing, the ratio of breadths of the icebreaker and the escorted vessels is important. During ice navigation, though the conditions of the ice and the contours of the ship are factors as well, in level ice a ship will form a channel behind it that is slightly wider than the widest point of the ship. Therefore, if the escorted ship is wider than the escort ship, the edge of the channel will come into contact with the forward shoulder of the vessel, causing friction and new resistance components, as the shoulder part cannot break ice effectively. It is therefore important to ensure that the widths of the two ships do not have this sort of proportion to each other. On this point, it is interesting to observe the widths of Russian icebreakers and icebreaking commercial ships.
