Feature 1 | TUGS Meet the fuel saving family
Te first two designs of a family of fuel-saving harbour tugs have been launched by IJmuiden, the Netherlands-based Offshore Ship Designers (OSD). Te Azistern family builds on lessons learnt during the OSD-led Green Tug project of 2009.
deliver 65-70tonnes bollard pull from a 31m loa hull and will be powered by two 1950kW diesel engines driving twin azimuthing stern thrusters. Te Azistern 2465 delivers 60-65tonnes bollard pull from a similar propulsion arrangement, but with a more compact 24m hull and a lower maximum speed. According to OSD the Azistern 3065 will be around 15% more fuel-efficient than comparable modern tug designs, due to the optimised hull shape. According to OSD the expected fuel efficiency saving for the Azistern 2465 is around 15-20%, but as the company has not conducted model tests yet this is only a prediction. Te shape of the Azistern hull is a direct
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result of the Greentug project. During the development of the Greentug design, the hull form went through computational fluid dynamics (CFD) optimisation. Furthermore, 1:10 scale model tests took place in a basin at MARIN (Maritime Research Institute [of] the Netherlands). As a result the form of the hull has been optimised for a 7-8kt mobilisation speed without compromising tug tasks. The challenge of hull form optimisation is to minimise drag and optimise the propulsion configuration, without sacrificing the manoeuvrability and sailing astern capabilities which are very important to tugboats. The hull form is optimised by performing the CFD calculations for up to seven different hull form variations. MARIN used its RAPID software to evaluate and optimise the pressure distribution and resulting wave pattern for different hull shapes. Both tug hulls have a hard chine
form which has undergone extensive tank testing to optimise energy saving
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he first two designs are the Azistern 3065 and the Azistern 2465. Te larger vessel (Azistern 3065) will
1:10 model scale tests of the Azistern 3065 have been carried out at MARIN (Credit: MARIN / Offshore Ship Designers).
during transit. It also results in a very low wash, which is important in a crowded harbour. The optimised hull results in less resistance and therefore better fuel efficiency. Te Azistern range uses conventional technology combined with highly optimised hull forms to deliver fuel saving and low-wake
TECHNICAL PARTICULARS Azistern 2465
Length, oa.........................................24.60m Beam, mld.........................................11.15m Depth hull at ½ L.................................4.60m Draught design...................................5.40m Bollard pull ahead.........................65tonnes Bollard pull astern ..........................60tonnes Speed, max transit.............................11.5kts Tank capacities Fuel oil .................................................75m3 Fresh water.........................................15m3 Lube oil .................................................3m3 Fi-Fi.............................................2 x 1200m3
harbour tugs. Te vessel’s propulsion is flexible to the customer’s needs and can feature either diesel-electric or hybrid propulsion depending on the operational requirements. To ensure that the vessel is simple to
build and maintain in shipyards around the world, a conventional machinery package has been specified. However, attention to fuel saving and efficiency is evident in the attention to detail. Uncluttered decks equipped with twin forward and aſt winches and good visibility ensure ease of handling for the three-man crew. The Azistern 3065 has a maximum
transit speed of 13kts and BP up to 70tonnes ahead and 65 astern and a 300kW bow thruster. Te compact hull has a gross tonnage of 423gt and a design operating draught of 5.40m. Te Azistern 2465 has a design draught of 5.4m, and a transit speed of 11.5kts, but its smaller hull size gives it increased ability to manoeuvre in crowded harbours. OSD previewed a scale model of the
Ship & Boat International July/August 2010
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