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January 2011 www.sname.org/sname/mt of 15 knots. Extra care had to be taken when designing the propellers to meet the opposing requirements of icebreak- ing at low speed and transiting open water at high speed. Figure 1 shows the shaft power-speed curve. Bollard pull. Adequate bollard pull is an important feature of icebreaking ships. Therefore, in addition to providing ade- quate propulsive power, we settled for relatively large propeller diameters and high over-torque characteristics of the propulsion systems. Figure 2 shows the ice thickness-ship speed curve. When recom- mending a required bollard pull of 190 tons, we took into account a one-knot margin. For commercial and other technical con- siderations, we opted for a design bollard pull of 180 tons. Over-torque. Present day icebreakers are almost always of the diesel-electric configuration. This type of propulsion enables better power management so that best possible system automation and redundancy can be achieved. All main diesel engines have their own cooling and fuel systems to ensure sufficient redun- dancy. It is also the icebreaker operators standard to provide for over-torque capability. Our design allows for 40% over-torque capability. Without this capa- bility, once the propeller stalls during icebreaking duties, the main generator engines will stall, leading to dangerous consequences. The chosen 40% electric motor over-torque adds considerably to the ships price but is the only sure way to ensure the ships operate successfully in heavy ice conditions. Larger fuel tank capacity. Connected with the higher power we proposed, the fuel oil capacity had to be increased pro- portionally. A ship that is smaller than the one we proposed would not have enough space to accommodate the autonomy of fuel supplies as stipulated by the owners requirement. Also, for added protection from accidental oil spills, fuel tanks were located inboard of double side and double bottom spaces. is is especially important in the fragile arctic environment. Outfitting. The icebreaker is provided with equipment specific to working in the harsh arctic environment. For exam- ple, the vessels towing arrangement is designed with high-power winches with auto mooring capability, and there are two bow thrusters that ensure success- ful operation in heavy conditions. This also secures redundancy of navigation with joystick steering near the oil termi- nal and in rescue operations. The ship also features heating of accommodation areas through a dual- channel heated ventilation system. e central heating of the ventilation air is arranged with steam boiler. Additional redundancy is arranged with electrical heating radiators in each accommodation space that is adjacent to external bulk- heads. Insulation of all spaces is designed for low temperature operation; in general, the thickness of rock wool insulation in the accommodation area is 150 mm. Special attention is paid to insulation arrange- ment so that condensation is avoided in +35 to -45°C outside temperature range. The cool bridges are built so that decks and bulkheads have a minimum 500 mm breadth insulation bridge. Double-glass thermo windows and additional winter glasses are installed in all cabin and ser- vice space windows. e navigation bridge windows also have electrical defrost heat- ing and warm air blowers. Model tests We selected the Finnish Technical Research Centre towing tank and Helsinki Technical University ice basin facilities for their independence and impartiality to carry out resistance, pro- pulsion, and ice model tests. Model tests in ice were carried out with 2 ice thicknesses, namely 1.0 m and 1.7 m. For the 1.0 m ice sheet, propulsion and resistance tests ahead and astern were Icebreaker BUILDERKeppel Singmarine OWNER/OPERATOR LUKOIL DELIVERY December 2008 CLASSIFICATION Russian Maritime Register of Shipping (RMRS) LL7 notation DIMENSIONSLENGTH OVERALL 100 mLENGTH LOAD WATERLINE 92 m BREADTH MOLDED 21.7 m BREADTH LOAD WATERLINE 21 mDEPTH MOLDED TO MAIN DECK 13.3 m DRAUGHT DESIGN10.5 m CREW 28 persons DEADWEIGHT 3,150 tons BOLLARD PULL 180 tons OPEN WATER SPEED 15 knots MAIN DIESEL ENGINES 4 x 5,760 kW (approximately 23 MW) AZIMUTH STERN THRUSTERS 2 x 8.4 MW BOW SIDE THRUSTERS 2 x 800 kW ELECTRICAL VOLTAGE 6.6 kV/440 V/230 V/60 Hz SPECIFICATIONS: VARANDEY