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Feature 2 | TUGS


Diesel-electric harbour tug drives green agenda forward


Low emissions remain high on the agenda as Offshore Ship Designers (OSD) sets to work on designing a 32m loa, 70tonne bollard pull, low-emission diesel-electric harbour tug, the Azistern 3270 DE, for IJmuiden-based Iskes Towage & Salvage, writes Nicola Stuart.


strong emphasis on lowering emission levels for harbour tugs in particular, as they are oſten required to operate in waters close to densely populated areas. Emission regulations in regions such as the US and Norway are stringent and, while the rest of the world is yet to demand the same level of reductions in emissions, operators such as Iskes Towage & Salvage are keen to be more environmentally friendly. Te contract is for two harbour tugs, which


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will be used for harbour tug duties in addition to some offshore duties. With this in mind, the design specifies the inclusion of a larger working deck; a low-resistance, low-wash hullform with good seakeeping characteristics; low fuel consumption and low emissions. While many OSD tug designs are around 30m loa, the Azistern 3270 is a larger 32m to facilitate its dual role. A relatively large deck crane has been included in the design brief to enable the tug to perform maintenance work for wind farms at sea and it will be fitted out with accommodation for a crew of seven. Te tugs will be built at Damen Shipyards, Hardinxveld, and delivery is expected in mid-2013. Iskes, also a leading partner in the original ‘zero emissions’ fuel-cell powered Green Tug


TECHNICAL PARTICULARS Azistern 3270 DE


Length, oa .........................................32.30m Length, wl ..........................................31.20m Breadth, mld .....................................12.50m Depth, mld ..........................................5.10m Draught, design ..................................4.10m Draught, keel ......................................5.35m Bollard pull ......................................70tonnes Diesel gensets ..........................3 x 1500ekW


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peaking with Ship & Boat International, Marc van der Zwaluw, general manager at OSD Holland, notes that there is


The adoption of hydrogen fuel cell technology will not become viable for harbour tugs until regulations and infrastructure can be put in place to support it.


project, will handle the operational aspects of the Azistern 3270’s design such as deck layout; accommodation and bridge layout.


Refined hullform Despite the successful work in developing the Green Tug design, Michiel Wijsmuller, managing director of OSD, says: “We can see the market is not yet ready for fuel cell power for harbour tugs, but we can take from the development work other aspects of the design which minimise emissions. Tis vessel will have a very refined and efficient hullform and a sophisticated power management system which will ensure that the gensets always work at their best efficiency.” Marc van der Zwaluw explains


that


adoption of hydrogen fuel-cell technology for the harbour tug industry is still some way off as the infrastructure to support it is not yet in place; greater access to hydrogen supply will


be needed for refuelling and regulations have yet to be fully realised. For vessels such as the Azistern 3270 DE, which will also have an offshore role, fuel cell-operation would restrict the vessel’s range. It is estimated that the design will see a


reduction in emissions of around 30% over conventional harbour tugs, says van der Zwaluw. He takes care to point out that this is only a guide figure; there are still decisions to be made on final battery size and engine configuration and so the figure will vary accordingly. With the aim of producing as low emissions


as possible, OSD has refined the hullform of the Azistern 3270 DE design using computational fluid dynamics (CFD) to optimise its resistance for transit speeds of 7-10knots. During onboard measurements, on one of Iskes’ tugs, OSD has calculated that as much as 35% of fuel consumption is used during transit. With the


Ship & Boat International January/February 2012


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