Gearing and coupling specialists exploit advances in materials and machining technologies to create systems offering higher efficiency, capacity and reliability
A comprehensive range of marine gearboxes from Renk extends from reversing units designed for inputs of 2,500kW to main gearsets for naval vessels capable of transmitting up to 40MW. The German specialist has also successfully promoted its Power-Take-Home (PTH) solutions for propulsion installations based on four-stroke or two-stroke engines.
Over 60 tankers have been supplied with such systems, and 14 x 16,500 dwt ships for Harren & Partner are specified with Renk RSVL 1060 gearboxes having PTO and PTH modes. The speed of the MAN 6L48/60 four-stroke main engine (developing 6,300kW at 500 rpm) is reduced to 107 rpm for the propeller shaft.
In addition to a PTO for driving a generator, the gearboxes are equipped with two multi-disc clutches and another gearwheel set. The shaft generator is configured to operate as a motor and provide a PTH drive mode – turning the propeller at 71 rpm – when fed with power from the 1,400kW diesel gensets. The extra cost of the system compared with a twin-screw installation for securing redundancy is low, Renk reports.
For propulsion plant based on a two-stroke engine directly coupled to the propeller, without reduction gearing, Renk suggests mounting a tunnel gear in the shaftline. The low speed of the main engine is thereby raised to a higher speed to drive compact standard generators for electrical power supplies.
As with the four-stroke engine installation, two multi-disc clutches and an additional gearwheel set are required to drive the propeller in PTH mode at reduced speed. Only a clutch in the shaftline is necessary to disconnect the engine when the PTH mode is deployed.
Single-input/single-output reduction gearboxes are available from Wärtsilä with input ratings up to 24MW in vertical and horizontal offset shaft configurations; twin-input/single-output sets can be delivered with up to 3.8m horizontal offsets. Special gearing solutions can also be designed and delivered.
Gearboxes can be supplied with built-in multi-disc clutches and one or more PTOs for driving shaft alternators, compressors or pumps. For single vertical and horizontal sets the standard PTO is primary driven (the PTO rotates whenever the engine is running); for twin-input/single-output sets the PTO is optionally primary or secondary driven (the PTO rotates whenever the propeller shaft is rotating). Two-speed PTOs/PTIs are available for the SCV75 to SCV142 gearbox types.
Most Wärtsilä gearsets are purpose designed with an integrated hydraulic system for both the gearing and the CP propeller. A separate hydraulic power unit for the CPP is thus superfluous, reducing installation costs at the yard and operational costs for the owner. For safety reasons, the gear mechanically drives the main pump for the propeller. All gears can be interfaced to a separate hydraulic power unit.
Gearboxes have been built to its own-design by Wärtsilä since the early 1990s at its Rubbestadneset factory in Norway, where recent investment has expanded production capacity and flexibility. A new extension houses assembly, welding and testing resources. Production is also undertaken at a facility in India.
A wide range of gearboxes is offered by ZF Marine which has manufacturing locations in Italy (ZF Padova and ZF Hurth Marine), Germany, Brazil and China (ZF Nanjing Marine Propulsion). Couplings, shafting, propellers (fixed pitch and CP) and controls can also be supplied, enabling customers to secure a complete integrated system from a single source.
Programmes are dedicated to different marine sectors, the Pleasure Craft portfolio providing mechanical gearboxes for sail and river boats (10kW to 100kW ratings) and hydraulic gearboxes (100kW to 1,400kW) for motor yachts. A SuperShift facility provides fast and smooth control while SmartCommand electronic control for CANbus installations facilitates automatic trolling and easy docking modes. A range of two-speed transmissions serve craft requiring fast acceleration.
Compact Fast Craft gearing solutions (1,400kW to 11MW) address the requirements of high speed ferries, military vessels and megayachts, where the design focus is on quiet running. Transmissions for defence vessels can be supplied to meet stringent shock standards or noise and magnetic signature limits.
A special range of horizontal, non-reversing systems are typically specified for waterjet-driven fast ferries, a sector from which ZF Marine continues to earn valuable business. A recent reference, the 112m-long Incat-built wavepiercing catamaran Norman Arrow, features four ZF 60000 NR2H reduction gearboxes, each transmitting power from a V20-cylinder MAN 28/33D engine (9,000kW at 1,000 rpm) to the Wärtsilä LJX 1500 waterjets.
Each gearbox is rated for a maximum input power of 12.4MW, the design having to suit the machinery room layout and satisfy space and weight limitations. A significant weight saving – reportedly more than 70 per cent – was also realised by using Centa composite shafting.
Triple ZF 53800 gearsets will serve an Auto Express 102-class trimaran fast ferry building at Austal in Australia with a propulsion plant based on three V20-cylinder MTU Series 8000 M71L engines (9,100kW at 1,150 rpm apiece).
Heavy duty Commercial Craft gearboxes (100kW to 16MW) are designed for propulsion plant in workboat, offshore support vessel, tug, inland waterway and deepsea cargo tonnage sectors. A new range of such gearboxes suitable for medium speed diesel installations from 2,000kW to 16MW was evolved from 2000, designed by ZF Marine in Germany and produced by ZF Padova. These units are now assigned to the joint venture company ZF-NMP in China in association with Nanjing Highspeed & Accurate Gear.
Large ZF heavy duty gearboxes are either reversing, non-reversing or direct drive (without a clutch), with a choice of single, double or triple PTOs for driving auxiliary machinery.
The ZF W17000 series was recently extended by W17100 and W17200 models with a higher reduction ratio range (up to 7.2:1), the series having previously been available for continuous duty commercial applications in reduction (NR) or reverse-reduction versions with a ratio range from around 2 to 4.5:1 and power inputs from 2,300kW to 3,000kW at 1,200 rpm.
Another new ZF Marine transmission, the 9000 series, is available in a number of configurations: parallel offset (vertical and horizontal), down-angle and vee-drive. With reduction ratios from 1.5 to approximately 5.2, the range is said to be suitable for all types of fast vessels and workboats with engines having ratings up to 3,700kW at 2,100 rpm.
Another German specialist, Reintjes, covers the gearing requirements of workboats, cargo ships, patrol and SAR craft, megayachts and fast vessels with an extensive standard programme supported by tailored solutions and two-speed designs. Designs are available for engine input powers up to 20MW.
Among optional facilities, an intelligent gearbox system (IGS) can monitor the change in propulsion speed and the current shifting pressure in the multi-disc clutch; as a result, says Reintjes, there is always an optimised pressure build-up and thus the maximum possible torque, whether while manoeuvring at low speed or during crash stops.
A trolling valve facility (GADS) – or regulated active speed control system – provides the operator with access to a propeller speed much lower than that achievable at the minimum engine idling speed. A PTO/PTI combination is also offered.
A new series of gearboxes is being progressively rolled out by Rolls-Royce, the latest 950AGHC model having a rated input torque rating of 130 kNm and up to 530 kNm of output torque. The basic single-input/single-output configuration with built-in clutch and thrust bearing is retained, while PTO options enable shaft generators to be driven. Provision is also made for electric motors to feed in power via a PTI for emergency propulsion or form part of a hybrid propulsion system.
Complementing and supplementing the established range, the new series benefits from design changes that mainly targeted increased stiffness and a more modular construction. The power, torque and shaft offsets were determined after an extensive analysis to address current and anticipated market demands in terms of engine power/speed and propeller rpm for a wide range of offshore, merchant and fishing tonnage.
Large reduction ratios are inherent in the design, the new 950AGHC gearbox offering a maximum ratio of 6.3:1, which is higher than the earlier series with this torque rating. Three more sizes are planned to join the new programme, while three models in the previous series continue in production to cover an overall torque band from 90 kNm to 1,200 kNm.
Texas-based Lufkin Industries has specialised in designing and producing gear drives since 1939, and is also active in repairing gearboxes of virtually any make. Its Power Transmission Division offers gearsets with weights from 300lb to 250 tons for input power ratings up to 62,500kW.
Lufkin’s programme for single- and multi-low, medium and high speed engine applications embraces single, reverse and two-speed forward drives with flexible shaft arrangements. Designs for SWATH and other specialised drives are also available, along with ‘drop in’ replacement gearboxes to fit existing installations.
A diverse range of tonnage – ferries, workboats, offshore supply vessels, anchor handlers and cargo vessels – is targeted, recent references including a pair of Lufkin RS2100HG gearboxes for the twin-screw pusher tug Robert T; three RS2118 drives for the triple-screw pusher Captain Otto Candies; and two RS2500 drives for the twin-screw pusher Western Navigator.
A pair of Lufkin RS2850 HG gearboxes with a reduction ratio of 7.515:1 serves the oil products barge pusher Ruth M Reinauer, each set transmitting power from a V16-cylinder MTU Series 4000 M60 engine delivering 1,735kW at 1,800 rpm. The articulated tug-barge system was completed in April by Senesco Marine for service on the US East and Gulf coasts.
A range of gearboxes manufactured by Mekanord complements the Danish company’s CPP propulsion system programme in serving engines with outputs from 150kW to 4,410kW. The portfolio includes two-step gearsets with reduction ratios up to 10:1; twin-input/single-output designs; gearboxes with extra long servo movements for large sailing yachts equipped with feathering propellers; horizontal offset gearboxes; and compact units for fast vessels.
Hydraulic servo systems are fully integrated in the gearsets for CPP pitch control, easing installation, operation and maintenance. Particularly high reduction ratios can be provided to serve low rpm/large diameter propellers and achieve higher thrust and efficiency. The gearboxes can also incorporate up to four PTOs, each with an independent hydraulic clutch, as well as PTIs to facilitate hybrid propulsion systems.
Austrian elastic coupling and torsional vibration damper specialist Geislinger recently delivered its largest-ever viscous-type damper, a Vdamp unit with an outer diameter of 1.6m for a Korean-built two-stroke engine installation. Only 19 working days were required between contract signature and delivery from the company’s Salzburg base, both enginebuilder and classification society DNV also giving approval within the same time period.
Type approval for the complete Vdamp range was recently gained from DNV, reflecting high quality standards from design to production. Vdamp units in low speed engine applications protect the propeller or camshaft against damage from torsional vibrations. Extensive research and testing was carried out by Geislinger on the silicone oils used, resulting in a calculation model enabling the damper to match the torsional vibration behaviour of the given system.
Highly torsionally flexible RATO couplings from Vulkan are designed to compensate for axial, radial and angular displacements of the connected engine or gearbox, with the torque transmitted by shear. The torsional stiffness and damping characteristics foster fine tuning of the torsional vibration behaviour of the drive system. The flexible part of the coupling may be single and/or multi row, depending on the size and stiffness.
RATO couplings – available with a maximum nominal torque rating of 2,000 kNm – will serve the world’s largest ropax ferries, due to enter service with Stena Line next year from Wadan Yards in Germany. A 33.6MW twin-screw propulsion plant is based on four MAN 48/60CR medium speed engines arranged in father-and-son pairs driving CP propeller shaftlines via Renk gearboxes.
Each 8-cylinder father engine will be connected to its gearbox through a Vulkan RATO-S 562Z coupling, while the 6-cylinder son engines will be connected through RATO-R382Y couplings. In addition, the gearbox PTOs will drive a 3,350kW shaft alternator at 1,800 rpm via a RATO-R 232Z coupling. The respective nominal torque ratings of the couplings are 250 kNm (for the father engines), 180 kNm (for the son engines) and 20 kNm (for the gearbox PTOs).
Composite shafts are another speciality of Vulkan, which reports a growing market for these lighter weight (and increasingly lower cost) systems in diverse applications.
Two new sizes of Centax-SEC couplings – the 188 and 288 – have extended Centa’s Super Elastic Coupling (SEC) range. The couplings are based on a highly flexible Centax element made of natural rubber or silicone and available in a number of hardness levels. In combination with a membrane link or bolt coupling, and a variety of flanges and hubs, solutions can be offered with high elasticity in all directions and a wide range of torsional stiffness.
SEC couplings can be applied in main, auxiliary and special-purpose drives for all sizes of vessel, installed between engine and gearbox or generator, or between gearbox and propeller shaft or waterjet. MP
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