Feature 4 | DIESEL-ELECTRIC AND ELECTRIC PROPULSION No shortage of alternatives
David Tinsley rounds up some of the latest attempts by propulsion unit manufacturers to balance low emissions with minimal complexity and maintenance requirements.
D
riven by considerations of overall vessel efficiency, emissions and hull space utilisation, operators and
designers are making increasing recourse to electric propulsion solutions. Nonetheless, it is oſten contended that such systems entail a high degree of technical complexity and elevated investment and life-cycle costs in comparison to conventional direct-diesel engines. In an initiative aimed at advancing the
practical appeal of electric drives, Norwegian company Inpower has developed an innovative system design featuring fewer components. Its patented PhiDRIVE system consists of the smallest possible number of components, and draws on technology applied in modern hybrid vehicles. Tis direct drive electric propulsion system
is distinguished by the use of permanent magnet-type generators. Since a power cable, dubbed the ‘electric shaſt’, is the only connection between the prime mover and the propeller, PhiDRIVE reduces the use of power electronics and cuts system energy losses, while providing better hull utilisation than diesel-electric or conventional mechanical drive arrangements. Efficiency gains and installation compactness, leading to improved power density, also stem from the adoption of permanent magnet machines. The repowering, in 2011, of
the 49m
Norwegian double-ended ferry Eiksund provided the debut installation for PhiDRIVE. The novel propulsion system retrofitted to the ford ferry combines PhiDRIVE with the azimuth rim-driven thruster(ARDT) design developed by compatriot company Brunvoll. In what constitutes the first example of rim-driven thrusters being used for main propulsion, an ARDT unit is fitted at each end of the vessel. Previous applications of rim-driven technology had been to tunnel thrusters. The thrusters have a variable speed,
controlled directly by the speed of the diesel generators through the Inpower Phi DRIVE ‘electric shaſt’ system. Te melding of ARDTs and Inpower’s drive system is reported to produce benefits including: a reduction in
30 In fact, the elimination of ‘wet stacking’ is
Stadt’s diesel-electric propulsion system, Stascho, has found its way onto the 34m purse seiner Meloyfjord.
investment and maintenance costs; minimal space requirements; improved propulsive efficiency and manoeuvrability; and reduced noise and vibration levels. The propulsion replacement project
for the Norwegian ferry, and the support provided by government agency Innovation Norway, allowed Inpower to fully validate and commercialise the PhiDRIVE system, and has presented new opportunities for the further development of azimuth rim- driven thrusters for main propulsion.
From bus lanes to the waves In a seminal development for the marine industry, Seattle-based Northern Lights is offering a new propulsion solution based on BAE Systems’ HybriDrive technology, applied to date in over 3500 transit (urban) bus applications worldwide. Offering benefits such as reduced pollution
and design flexibility, the hybrid electric configuration uses power control electronics to feed energy from the diesel generator directly to electric propulsion motors, or to a bank of batteries for later direction to the propulsion or auxiliary consumers. The energy storage element enables periods of vessel operation without the engine running, and optimises energy flow and utilisation. The HybriDrive marine system can be
sized and customised to a user’s precise needs and can also be configured as an auxiliary power system to deliver a vessel’s service AC power without the energy waste and pollution associated with engine under-loading.
regarded by Northern Lights as one of the main attributes of hybrid arrangements. Te system enables the engine to operate at its optimal fuel curve at all times, helping to ensure that power demand is met without large variations in load, and resulting in reduced maintenance over time.
Fishing for business During October 2011, the Stadt Stascho diesel-electric propulsion system gained its fourth order in the Norwegian fishing vessel market through the commissioning of the purse seiner Meloyford. The compact size and low noise
characteristics of the Stascho diesel-electric system are well suited to the requirements of vessels employed in fisheries and research. Te 34m Meloyford was built at the Blaalid yard in Norway and draws 1400kW of propulsive power from five gensets. Tree previous purse seiners have been equipped with the Stascho system, which was first employed in the 86m seismic research ships Sanco Spirit and Sanco Star. Stadt’s development of its new AC drives was
shaped by a bid to reduce system complexity and extent, with the parallel targets of increasing reliability, reducing downtime risks and extending service life. Although the company’s bypass-switching technology was seen as key to ensuring low energy losses, subsequent results and independent verification have led Stadt to promote the Stascho solution as incurring negligible or zero losses, rather than being simply of ’low loss’ character. In the Stascho drive system, sinusoidal
voltage and current is supplied to the electric motor and back to the switchboard. Tis results in very low harmonic disturbances in the main switchboard and motor, and dispenses with the need for transformers and filters, giving rise to a more compact configuration.
Battery back-up Scotland’s marine industries are putting down a new marker for more environmentally-
Ship & Boat International January/February 2012
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