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Feature 2 | PASSENGER AND FREIGHT FERRIES


compliant, thereby avoiding the additional regulatory costs associated with non HSC-compliant, comparable-speed vessels of traditional construction. Although the economic recession and fuel


price volatility have halted the trend towards higher design speeds in other sectors of the shipping industry, swift transit speed remains an important competitive factor in the shortsea ferry business. Passenger expectations are an overarching consideration, and the indications are that there is a still a desire among passengers not to have to travel at speeds under about 16knots. An aluminium hull form, it is contended, allows higher speeds to be obtained for the same propulsion-related costs as those entailed with steel-hulled tonnage. While conferring relative cost savings,


Austal’s designers have also sought to ensure that the new medium speed ferry range would ensure the high levels of manoeuvrability, stability and seakeeping demonstrated by the faster catamarans and trimarans turned out by the Henderson yard and its associated USA builder. So as to confer the requisite manoeuvrability in harbour, the proposed trimaran features drop-down azimuthing bow thrusters, while the catamaran can be specified with a drop-down thruster or tunnel thrusters, according to an owner’s wishes. In addition, high-liſt rudders are aligned with the propellers in each of the designs. As one of the pre-eminent drivers of


aluminium-hull fast ship technology, the Western Australian firm suggests that the dimensions of a typical multi-hull not only allow for a more open, comfortable passenger space, but also demonstrate superior stability and hydrodynamic efficiency compared to a monohull. The nomination of controllable pitch


propellers in conjunction with multiple main engines presents operating and scheduling flexibility, suited to the particular needs of ferry services, where traffic composition can change substantially from day to night and from summer to winter. Te arrangements mean that power can be better matched to needs at any one time, for instance allowing full-speed navigation on all engines during day passages, or reduced engine operation for night crossings when the emphasis may be on freight carrying. To achieve further efficiencies, propellers that are not being used may be feathered, reducing drag and


90


Stern view of the medium speed version of Austal’s 102m trimaran, with three controllable pitch propellers driven by medium speed diesels.


fuel consumption. A drive-through configuration has been


adopted for the new design range, using both bow and stern doors, in recognition of the importance of expeditious turnrounds to both service performance and vessel productivity. Fast turnrounds bear significantly on total round-trip times, enabling operating speed to be kept to more economically-favourable levels. The trimaran member of the medium


speed family is a variant of the 102m next generation design, of which the first representative has now been completed and is lying for sale at the company’s Henderson yard. Te intake capacity of the new version is almost identical, at 1165 passengers and 145 cars plus 190 truck lane-metres, or alternatively 254 cars all-told. However, whereas the original design is installed with three examples of MTU’s potent 20V8000 high-speed diesel driving Wartsila LJX waterjets, the new addition to the portfolio would be laid out for three medium-speed main engines of 320mm-bore, driving controllable pitch propellers. Engine choice could be Wartsila’s 9L32


type or MAN’s 9L32/40 diesel, to deliver speeds of up to 25knots at 600dwt. By contrast, the existing 102m vessel is attributed with a 39knot speed, albeit at 340dwt. Overall fuel consumption of the medium speed trimaran, including the generators, is stated as no more than 2.1tonnes per hour at 85% maximum continuous rating(MCR) of the


main engines. Te existing vessel is attributed with a 4.9t/h consumption on the basis of 39 knots at 90% MCR on 340dwt, and with ride control fitted. The 100m catamaran of the medium


speed range has been conceived for operators requiring a somewhat higher deadweight without the need for the superior, rough weather seakeeping capabilities afforded by the trimaran. With a maximum deadweight of 800tonnes, the catamaran has seating for 1000 passengers and 154 cars plus 205 truck lane-metres. Maximum utilisation of the garage spaces for cars would equate to 208 units. Four medium-speed diesel engines would


form the propulsive power installation, using seven-cylinder examples of the 320mm-bore designs also favoured for the new trimaran offering. Te options are the Wartsila 7L32 or MAN 7L32/40, driving controllable pitch propellers. In combination with Austal’s refined, lightweight catamaran hull form, overall fuel consumption, including that of the auxiliaries, would be just 2.17t/h at 85% MCR on 800dwt. From an environmental perspective,


each vessel in the range is eligible for Green Passport classification notation, a feature that is available for all ships from Austal. Te largest catamaran ordered to date from the Australian yard, BornholmerFaergen’s 113m, 40knot newbuild due for handover next year, has in fact been specified to Green Passport credentials. NA


The Naval Architect September 2010


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