Feature 4 | ALTERNATIVE PROPULSION
of anchor-handling tug/supply (AHTS) vessels. The main goals are to minimise total installed main and auxiliary engine power and to engender efficiency over the ship’s full operating range. The concept is illustrated in application to a 91m class of AHTS, the Vik-Sandvik VS491 CD design. In a hybrid configuration, the twin controllable pitch propellers can be driven by a combination of diesel engines and variable-speed electric motors. For each shaftline, one Wärtsilä main diesel engine and one electric motor are connected to a Wärtsilä gear. The propeller can be driven by the diesel engine, the electric motor, or by both. The main engines have a power take-off
(PTO) at the front end, driving a 3000kW shaft generator at a nominal speed of 720rev/min. With this arrangement the main engine can be used as the propulsion engine at variable speed, or at constant generator speed, or as a generator driver disconnected from the propeller. The reduction gears necessarily have two clutches each, one for the diesel engine and one for the electric motor. A hybrid diesel mechanical and diesel
electric propulsion system developed by the Ulstein Group of Norway is due to make its seagoing debut in 2009 through the deliveries of two DP2-class, A122-type vessels conceived for both anchor-handling and offshore construction tasks. Installed with 19,500kW of engine power to achieve a considerable bollard pull of 260t, the innovative design embodies powering arrangements based on two main diesel engines and five main genset drives. The rationale for the hybrid powering
system is to permit the vessels to switch between diesel-mechanical and diesel-
Fuel-cell passenger vessel Alsterwasser on the Hamburg waterway system.
electric propulsion in accordance with changing power needs across the operating profile, while combining the two in hybrid mode so as to achieve maximum pulling power. The dual power provisions capitalise on the main strengths of each mode in a breed of vessel subject to very substantial and rapid changes in power requirements, promising savings in overall fuel usage, with attendant benefits in reduced environmental impact. California is about to see the service
entry of a hybrid, diesel-electric tug, which will use batteries and an active power management system to minimise engine running, with attendant savings in fuel and atmospheric pollutants. The arrangements are predicated on the considerable amount of time overall that tugs spend on standby and in mobilisation and demobilisation phases. As a modified version of Foss Maritime’s
Dolphin-class of 78ft harbour tug, the so-called Green Dolphin (see Tugs feature on page 24 for more information on this vessel) hybrid features two 600hp battery packs coupled to two 402hp generator sets. The battery system will be brought into play at lower power demand. The Green Dolphin’s modular design can be applied as a retrofit technology for existing tugs, and also enables recipient vessels to incorporate future energy storage improvements such as enhanced battery packs and hydrogen fuel cells.
SkySails system fi tted to Michael A (credit: SkySails).
40
LNG usage grows Norwegian initiatives to use LNG as a marine fuel are expressed in the gas engine systems in a new generation of
double-ended ferries built to serve the country’s west coast highway network, and in the uptake of LNG-burning plant in small coastal gas carriers and offshore support vessels. Most recently, Seatrans has specified an LNG-fuelled Bergen main engine for each of two ro-ro equipped multipurpose freight carriers ordered in India for subsidiary operator Sea-Cargo. Stringent
requirements relating to
nitrogen oxide (NOx) and sulphur oxide (SOx) emissions, stipulated by the Norwegian ministry of transport and communications for ferry connections on the national highway network, have prompted the adoption of
‘cleaner’
powering systems. Pivotal to these is the usage of LNG fuel. The government has encouraged
the development of the gas supply infrastructure along the coast, bringing Norwegian-derived LNG within the reach not only of fjord ferries, but also coastwise traders, offshore support ships, and other vessels. There are, of course, economic merits to the strategy, given Norway’s role as a leading gas producer, in addition to the benefits of alternative fuel usage in helping the country to achieve environmental targets in cutting carbon dioxide (CO2
),
NOx and other atmospheric pollutants. The five double-ended ferries delivered
by Aker Yards in 2007 to Norwegian transport group Fjord1, to connect sections of the country’s main western road network, use reciprocating main machinery capable of burning both LNG and diesel fuel, within an electrical power generation and propulsion system. The core technical stipulation for the
Ship & Boat International November/December 2008
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