Marine Log - February 2008 - (Page 35)

PROPULSION EVOLVING PROPULSION OPTIONS FOR DIESEL ELECTRIC SHIPS O ver the last several years, dieselelectric propulsion systems have become increasingly more popular in offshore vessels. Recognizing this trend, Germany’s Schottel GmbH began development of a ducted version of its Twin Propeller Schottel Combi Drive (SCD). Back in 2006, Schottel unveiled the Twin Propeller SCD. Five vessels with 16 units are currently in service and another 10 vessels will be introduced with the Twin Propeller SCD by 2009. The Twin Propeller SCD is used in vessels that operate at medium to high speeds. The ducted propeller version, says Schottel, is better suited for vessels that operate at the lower speed range and at static thrust. For example, the ducted Twin Propeller SCD is well suited for diesel electric-powered offshore vessels such as anchor handling tug supply vessels (AHTS), seismic research vessels and cable ships that often operate their engines at partial load and dynamic positioning mode. One of the advantages of a diesel-electric propulsion system is its power management system, which ensures that only the required power is generated and distributed to the various units in the vessel. In combination with a ducted fixedpitch propeller, as in the SCD, such a system offers greater efficiency, especially in the low load range. In a diesel-electric fixed-pitch system, the required thrust is generated via the electric motor speed. The generators run at the optimized operating levels—as do the fixed-pitch propellers. Furthermore, for low to medium vessel speeds, a welldesigned fixed-pitch propeller with frequency control is more efficient at the rated speed than a controllable pitch propeller. The diesel-electric concept allows for a more flexible design of the vessel’s interior, resulting in a substantial increase in usable space. One of the first shipowners to place orders for the ducted Twin Propeller SCD was Great Offshore Ltd., Mumbai, India. It ordered a 150-ton AHTS with diesel-electric propulsion with two ducted SCD 3030’s at Bharati Shipyard in Mumbai. The two SCD 3030 units have a power rating of 3,300 kW each and are supported by two retractable SRP 1212 ZSV Rudderpropellers, each rated at 1,500 kW, and an STT 1 transverse thruster. Great Offshore will put the new vessel into service at the end of 2008. VOITH SCHNEIDER PROPELLERS AND DYNAMIC POSITIONING For its 85.8m diesel-electric Platform Supply Vessel (PSV) Edda Fram, Norwegian offshore vessel operator Østensjø Rederi AS took a different approach. Handed over by Spain’s Astilleros Gondan AS in Sept. 2007 and classed by DNV, the vessel is equipped with two diesel-electric driven VSP36R6 Voith Schneider Propellers. Propulsion power is supplied by two 2,500 kW AC asynchronous water-cooled propulsion motors. It was the first such vessel to use VSP’s Nozzled single Schottel Combi Drive 2020 The 85.8m Edda Fram was the first platform supply vessel to be outfitted with Voith Schneider Propellers for propulsion. A sister vessel under construction at Astilleros Gondan will also be fitted with VSP36 R6 Voith Schneider Propellers. Joint testing conducted earlier by Østensjø Rederi AS and Voith Turbo Marine at Marintek and SVA Vienna showed the excellent propulsion efficiency of the VSP solution across the entire operational draft and speed range. Tests also showed that considerable fuel savings was possible across the offshore supply vessel’s entire operating range. Additionally, the VSP showed excellent sea-keeping behavior. The VSP also offers: • Redundancy • Controllability • Fast and extremely precise thrust control for DP mode • Long service life and reliability • Built-in CP characteristic allows the optimum adaptation of the entire power train to the different operation modes. Voith Schneider Propellers offer quick FEBRUARY 2008 MARINE LOG 35 www.marinelog.com http://www.marinelog.com

Table of Contents Feed for the Digital Edition of Marine Log - February 2008

Marine Log - February 2008 Contents Editorial Second Thoughts Update Inside Washington Cruise Growth: Driven by Megaships and Europe Another Piece of the Short Sea Transport Puzzle Putting Together a More Advanced Jones Act Tanker Evolving Propulsion Options for Diesel Electric Ships In Search of Smarter Shipbuilding Seatrade Peview Events Newsmakers Tech News Contracts Website Directory Infodirect ML Marketplace Opinions

Marine Log - February 2008

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