Podded Propulsors Gain Wider Acceptance

The growing uptake of integral electric-driven, podded propulsors in the most capital-intensive sector of the cruise shipping industry, has forever altered the established position of conventional propulsion systems in an important segment of the market. Having established a foothold in the offshore sector, the concept will no doubt find increasing application with the next upswing in investment by the offshore oil and gas industry. Once conservatism has been overcome in various quarters of the shipping business, and once the net acquisition costs of such systems reach more acceptable levels for a broader band of the shipowning community, usage of the technology will no doubt spread to other spheres. The relative paucity of orders for podded drives in areas where precision handling is paramount, as with icebreakers, cableships, ferries and specialized tankers, belies the extent to which such systems are being written into draft proposals or discussed at the project planning stage. The concept is especially apposite to vessels with varying service profiles, particularly where high maneuverability is required. The long-term sales impact of the industrial commitment from the design engineering and manufacturing side cannot be understated. In each case, podded propulsors are the products of pairings entailing major players in propulsion and electrical engineering, entailing direct or indirect links with leading shipbuilders, in certain instances. As a progression on thruster technology, the basic principle is that the conventional shafting, propeller and rudder system is replaced with a 360-degree rotatable thruster unit also encapsulating the electric motor. Space savings are thereby achieved within the hull, while the efficiency losses from reduction gearing, long shaftlines, rudders, stern thrusters and also brackets and bossings are eliminated. The market is opening up not only because of the improved propulsion efficiency, design flexibility and also reduced noise and vibration conferred by the generic type, but also because of its virtues in generating high steering forces, and achieving extremely high levels of maneuverability, invariably at lower power cost than with conventional arrangements. The first cruise ship application of podded electric drive was Carnival's 70,400-gt Elation, commissioned in early 1998 and fitted with two 14-MW, Finnish-developed Azipod propulsion units. The most widely employed system to date, Azipod was originated by ABB Industry and Kvaerner Masa-Yards (KMY), but Italian shipbuilder Fincantieri is also a shareholder today in the system's proprietary company. Current newbuild references include the entire Carnival group program, Royal Caribbean's prestigious Project Eagle series, as well as Hapag-Lloyd's Europa, all at KMY yards, and Holland America Line's sister to the Rotterdam from Fincantieri. The Finns, with a long track record in thruster technology, were the leaders in the podded drive concept, first applied in the form of a 1.5-MW Azipod unit to a Finnish waterway service vessel in 1991. Although the competing Mermaid system is building market share, the Azipod name is wholly synonymous with what must rank as one of the marine industries' most innovative, pragmatic developments over the past decade. As a measure of its influence, the Azipod system figures in each of the substantial number of cruise ship newbuilds currently in hand and on order at KMY. By April this year, confirmed orders for the device had totaled 40 units of an aggregate 487,000-kW, including a total of 29 in 13 cruise ship applications. The adaptability of the Azipod technique is implicit in a design range which extends from just 500-kW to approximately 25-MW. The commissioning towards the end of last year of two Azipod-equipped ice-strengthened platform supply vessels, for operation in the Caspian Sea, underlined its versatility. While each of Royal Caribbean's Voyager of the Seas-led Eagle class is being equipped with three 14-MW pods, the biggest unit power concentrations specified to date are the 19.5-MW motors in each of the twin Azipod installations for the shipowning group's Vantage-class from Meyer Werft. The newbuilds in Germany will have added distinction as showcases for the U.S.-engineered combined gas and steam turbine, integrated electric drive system (coges). The coges concept is similarly being used for the Millennium cruise ship program at Chantiers de l'Atlantique, but with propulsive effect to be conveyed by 19.5-MW Mermaids. No longer just a fabled creature of the sea, the Mermaid is now an embodiment of advanced marine technology, which has caught the eye of the cruise ship and offshore sectors. Following its milestone selection for Royal Caribbean's Millennium cruise ship newbuild project in France, the Mermaid pod propulsion system has been specified for Radisson Seven Seas' luxury cruise vessel from the same yard, Chantiers de l'Atlantique. Parented by Kamewa, as the Swedish arm of the Vickers group, and electric drive specialist Cegelec, the system now has a rather broader ownership spread, as a result of the creation of the new Vickers-Ulstein Marine organization and Alstom's takeover of Cegelec. In-house connections play a vital role in business development, as demonstrated by the current level of recourse to Mermaid for newbuild orders at Chantiers de l'Atlantique, the primary shipbuilding entity within Alstom. The latest contractual reference in France calls for the delivery of two 8.5-MW podded electric drive, azimuthing units for the $280 million, 46,000-gt Seven Seas Mariner. It underscores the growing popularity of podded systems, which eliminate the need for long shaftlines, rudders, rudder machinery, and stern thrusters, freeing large amounts of space onboard, and which provide much greater maneuverability and steering capability than the conventional alternatives. Due to be ready for delivery at the beginning of 2001, Seven Seas Mariner will become the largest vessel operated by Radisson Seven Seas, in a project involving the participation of the Monaco-based ship management company V. Ships. The 360-cabin newbuild will become the industry's first all-balcony, all-suite cruise vessel. She testifies to the positive view of the cruise ship market held by the Minneapolis-based Carlson Group, which plans to expand the Seven Seas fleet by one vessel per annum over the next five years from 2000. The first two Millennium-class 85,000-gt cruise ships booked with Chantiers de l'Atlantique by Royal Caribbean are intended for operation with its subsidiary Celebrity Cruises. The project signals the introduction of gas turbine propulsion and the coges concept to the cruise market, and will employ two 19.5-MW Mermaid podded units. The build program at St. Nazaire has been extended as a consequence of options on third and fourth Millennium being exercised recently by the Royal Caribbean group. While the initial ships are expected in June 2000 and January 2001, deliveries of the second pair into Celebrity's employ are slated for August 2001 and March 2002. It is understood that the technical design of the latest additions to the workload will be identical to that of the first two vessels, which points to the likelihood of a further tranche of contracts for the Mermaid system before too long. With the Radisson cruise ship deal, the sales tally for Mermaid reached 18 units in a comparatively short period of time, while Royal Caribbean's new additions to its Millennium program hold out the prospect of orders for another four 19.5-MW drives. Podded propulsion is also to be adopted for the two 48,000-gt cruise ships just ordered from Chantiers de l'Atlantique for operation with Festival Cruises of Greece. It is understood that consideration is being given both to Mermaid and to a rival system. Mermaid achieved its market breakthrough last year with a four-unit installation on the Sedco Forex semi-submersible drilling exploration platform Sedco Express. Each of the rig's azimuthing pods is rated at 7-MW. The Sedco Forex deal involved two such platforms, and the company went on to order a similar package of four pods for a third rig. The Mermaid propulsion arrangements form part of a package from Kamewa and Cegelec encompassing main distribution switchboards, automation and dynamic positioning systems. Development work on Mermaid constituted one of the most extensive projects in the history of Kamewa's Hydrodynamic Research Center in Kristinehamn, Sweden, where model testing of azimuthing thrusters has been conducted for decades. "The testing has ensured that Mermaid offers the lowest possible noise and vibration levels," said Mermaid Propulsion project manager, Jan Pettersson. "This, in turn, means an unusually high level of passenger comfort. Safety is increased by excellent maneuverability, and superior crabbing and crash-stop capabilities," he added. While Germany's premier shipping group, Hapag-Lloyd, selected Azipod drive for its prestigious Europa cruise ship project, the German contender in the field of podded propulsion systems has achieved its market breakthrough courtesy of a Swedish shipowner's newbuild project. The endorsement of the German-engineered alternative is all the greater in its significance for the prominence of Scandinavian technology in the field. The solution devised by steerable propulsion specialist Schottel in conjunction with electrical engineering group Siemens differs substantially from the other options available through the adoption of tractor and pusher propellers at each end of the podded drive. The Siemens-Schottel Propulsor (SSP) is due to make its operational debut next year, having been selected for Rederi Donsotank's 19,500-dwt chemical product tanker booked with Shanghai Edward Shipyard in China. The contract for the newly-developed pod was actually awarded by the shipbuilder, which is partly German-owned. Since the main contestants in the market have been successful in attracting serial contracts, repeat, batch and potentially volume production will impact on manufacturing economics and enhance the competitiveness of the relevant products. Significantly, therefore, Schottel has made dedicated provision for the output of SSP units from the facilities of Wismar Propeller und Maschinenbau, acquired from Dieselmotoren-Werke Rostock. Renamed Schottel-Antriebstechnik, the plant will be the subject of a five-year DM 30 million investment program, and will be the point of manufacture, assembly and testing of SSP propulsors. The Swedish tanker recipient of the entirely German-conceived system, in its SSP7 configuration with an output of 5.1-MW, will be constructed to the highest ice class notation of Det Norske Veritas for year-round duties in the Baltic trade. One of the characteristics which favored SSP's selection for the Donsotank vessel, designed by the Uddevalla firm FKAB, was its ease of fitting, a factor salient to its use in a project in China. Modular design and the avoidance of complex air cooling arrangements, makes for a relatively straightforward installation. Perceived strong points of the concept, from the contractual owner's standpoint, are improved efficiency compared with conventional propulsion systems, outstanding maneuverability and ice-going capabilities, low maintenance requirements, and space-saving attributes, enabling more of the hull envelope to be used for cargo carrying. Schottel and Siemens have jointly developed the 360-degree rotating SSP using the SVA institute in Potsdam for tank and cavitation tests. It is claimed to offer 10 percent higher propulsion efficiency than conventional systems, and is targeted at applications in the 5-30 MW range embracing the cruise ship, large ferry, reefer, products and chemical tanker, icebreaker, and offshore and sectors as well as the naval market. The forward, or tractor propeller is located ahead of the bulb, and some of the rotational energy in the flow downstream is recovered by the strut and two fins on the bulb, with water then flowing through the aft propeller to gain added thrust. Besides the twin propeller technology, the other pillar of the system is the slim-line, highly efficient development input from Siemens, in the shape of a permanent magnet, longitudinal-flow motor (LMF). Each end of the armature is coupled directly to a propeller so that the two propellers rotate in the same direction. A fourth European pairing, drawing together Germany's STN Atlas Marine Electronics and the now UK-owned, Dutch propeller and waterjet specialist Lips, has developed a podded system known as Dolphin. The initial offering was based on five basic sizes from 9 to 19MW.