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October 2011 www.sname.org/sname/mt surface on a round trip (average of loaded and unloaded condition) is reduced by 16% compared to the baseline design. is is estimated to reduce fuel consumption by 11% as the main resistance is from friction on the wetted hull surface. To facilitate trim and list control during cargo operations, Triality has ve longitudinal cargo sections, i.e., two longitudinal bulkheads more than the baseline design, and is intended for up to three cargo seg- regations. e oil outow index is improved by this arrangement com- pared to the baseline design, which N F B O T U I B U U I F D P O T F R V F O D F T P G B possible accident involving an oil spill are reduced. Each cargo tank is loaded/unloaded along its full length, thereby eliminating the need for water ballast to control hull-bending moments. The ballast-free design has no possibility of using ballast water to adjust the trim, but Triality incorpo- rates some 3,000 tons of freshwater onboard, which in a closed system can be shifted between the fore peak and aft peak tanks as needed. The Triality ballast-free hull design results in a heavier hull structure. e increased hull steel weight is estimated to be in the range of 4,000 tons depending on the detailed baseline hull design. Current practice for VLCCs is a single-screw arrangement with a propeller diameter of up to 10 m. e Triality draft at the aft perpen- dicular in the unloaded condition is 9 m or less, and has therefore been designed with a twin propeller arrangement, with propeller diam- eters of approximately 7 m. This has the added benet of propulsion redundancy, which increases safety. For improved propulsion eciency, one propeller is placed forward and overlaps the other. LNG fuel LNG-fueled ships have operated successfully for a long time. For example, LNG tankers using boil- o gas for propulsion have operated for some 30 years. There are cur- rently just 23 vessels in operation, other than LNG carriers, which are fueled by LNG. ese are relatively new vessels and all have been built during the last 10 years. All of them are small and operate in the coastal waters of Norway, and another 20 vessels are on order. Rules for such propulsion have existed for the past 10 years. The IMO has already developed interim guidelines for gas-fueled ships and the technical content is to a great extent based on and identical to the rule developments carried out by the Norwegian Maritime Directorate and DNV as pioneers in this field. These guidelines are intended to become International Gas Fuel Code at a later date. ere is a perception that LNG fuel for ships is an alternative for short-sea shipping only. However, the Triality project demonstrates that LNG fuel also is a viable option for ocean-going shipping. The Triality model has two slow-speed, two-stroke dual- fuel MAN main engines?ME-GI engines. MAN ME-GI engines have operated successfully on land for power plants. In the gas mode, these engines burn 5% oil as pilot fuel to ignite the gas. e engines S F R V J S F I J H I Q S F T T V S F H B T B U approximately 300 bars, at a tem- perature of some 45°C. An exhaust gas recirculation (EGR) system has been developed and successfully tested by MAN and is assumed installed on Triality to reduce the NO X emissions. Two engines represent increased redundancy compared to a standard VLCC. Wartsila is also working on a ver- sion of a two-stroke engine with similar output. Triality uses marine diesel oil (MDO) as pilot fuel. MDO back-up capacity for 10 days of pure oil fuel operation is included in the design. Using MDO rather than heavy fuel oil (HFO) as pilot and back-up fuel has an additional cost, but it also has the benefit of avoiding complex heavy fuel oil installations, including asso- ciated heating arrangements. e auxiliary engines are dual- fuel engines for low-pressure gas. The boilers are of the triple-fuel type, enabling the use of MDO, natural gas, or recovered VOCs from the cargo. e LNG fuel is contained in 2 x 6,750 m 3 C-type pressure tanks located in deck houses on the aft part of the cargo deck. C-type tanks have been widely used as pressure ves- sels. e deck houses include tank insulation and are inerted by nitro- gen. Detailed studies may reveal that it is more favorable to locate the e Triality hull shape has low block coecients of 0.6 and 0.52 in loaded and unloaded conditions, respectively.