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Year


Kind of damage


Dents with cracks


Dents,


corrugation without cracks


Holes in plating


Damage to rudder blades


Damage to shafts, deadwoods


Damage to steering


arrangement


Damage to other shipboard equipment


- - - - - - 7 8 1.9 10.1 6.3 1.3 5.1 19.7 5.6 - 1.4 25.7 8.8 0.9 - 5.4 9.6 1.4 - 7.4 2.9 2.9 1.5 4.7 4.7 2.4 0.8 6 9 2 8 12 7 4 6 11.4 6.7 1.9 2.9


1981 1982 1983 1984 1985 1986 1987 1988 21,5


26.8 55.7 46.5 32.7 31.9 32.9 50.7 30.9 54.4 55.9 23 31.5 45 31 32 Average 31.8 43.8


provide assistance and communication, weather


information, amount of


icebreakers, their technical characteristics. Experience of ice navigation of a piloted vessel’s crew is very important to avoid possible accidents. During Arctic ice navigation an


icebreaker executes navigation, anything from one to three or more transport vessels (in autumn). Te route of navigation of vessels has a large range to cover: more than 1000 miles, including a river section of about 300 miles. Caravans consist usually of vessels of


• Diagrams determining the parameters of safe ice pilotage when a vessel rides aſter


ballast») determining possible safe speed in case of unassisted navigation in ice. Tese diagrams involve all kinds of ice cover that vessels are capable of overcoming without icebreaker assistance.


an icebreaker. Tey are used also to select the power plant operation mode.


Te tactics of ice navigation is an outline of


special methods to provide safe transit in ice conditions of single vessels without assistance of an icebreaker or as part of a caravan (a group) of vessels under the icebreaker’s navigation. The actions of navigators who choose


the route, mode and speed of the vessel, determine the safety in ice. Navigation in very open pack ice is less challenging (compactness 1 - 3 points), as the vessel can easily manoeuvre, passing by separate ice floes. Navigation in open pack ice (4 – 6 points) requires skills to choose in-time directions of open-water canals (fractures) located closed to the general course of the vessels. Te task of navigation in close pack ice (7 – 9 points) is to detect and use the weak ice areas to pass. Such areas can be the strips of open pack ice, small fractures and water paths in compact pack ice, strips of less strength, less hummocked and more broken ice.


The Naval Architect July/August 2011 Icebreaker navigation is still the main


way to provide vessels with successful and safe winter navigation in heavy ice conditions.


Icebreakers carry out


navigation of single vessels and caravans as well as the creation and maintenance of the navigational ice channels in areas near ports. Te task of the icebreaker master is to


minimise losses of navigational speed of a caravan that consists of different types of vessels. Choosing the route depends on the information about the real ice conditions on the route and the forecast (ice and wind) for the passage period. Te master should choose the general direction of motion and then divide it into separate parts depending on its ice conditions. On each part of the route, the master can apply their own tactical methods of navigation and pilotage. Well-planned routes provide for the successful traffic of cargo vessels in icy conditions. If the ice conditions are complicated or suddenly gets worse, the ice navigation of a big caravan becomes impossible, and it is necessary to determine a place of moorage for a vessel or a group of vessels in advance. Tactics of ice navigation of a caravan of


vessels is based on using all the available information, including the technical data of the vessels in caravan and their amount, ice conditions and its forecast, means to


different types, power and hull strength. To pilot such a caravan, the main principle is that under collection of a caravan: the vessel with the highest strength hull should precede the vessel with a weaker hull. If several icebreakers navigate the caravan, the weakest vessels proceed aſter support icebreakers. Te more powerful and higher strength vessels travel aſter the main icebreaker. To avoid delays in navigation due to ice chipping around the weak vessel, icebreakers should tow the weak vessel so that the speed of the caravan does not decrease. Prominent features of arctic winter


• Polar night demands application of the spotlighting within caravan and eliminate


navigation that is necessary to take into account to provide the safety of transport vessels are as follows:


helicopter surveillance of ice conditions. • Low air temperatures (up to -40o


С)


• Snow and ice coating of the hull and superstructures worsens the stability of


decrease the strength of metal, including tugs and strings that complicate all towing operations and cargo handling.


• Jamming of an icebreaker in a difficult ice area that demands a long time to free


vessel and complicate all deck operations.


slows down the assist for vessels nipped by ice.


navigation


The newly raised problem of arctic is


rendering icebreaker


navigation to large-capacity tankers, which have a larger hull breadth and so increases the breadth of icebreakers, and consequently


57


Table 3. Statistics (%) of accidental ice damage in winter navigations.


Feature 4


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