As more vessels are built with hybrid propulsion for operations in shallow waters and inland waterways, there are greater demands on thruster manufacturers to come up with solutions
Veth Propulsion and Twin Disc have together developed propulsion that uses both diesel and electric inputs, and propulsors for shallow-water vessels. These are increasingly required because water levels have fallen over recent years in rivers, and ports are developing their resources more effectively by opening shallower areas to marine services.
“The effects of climate change mean the water levels of many European rivers have declined dramatically in recent years,” said Twin Disc vice president for sales Timothy Batten. “The capability to operate in shallow waters is increasingly vital, otherwise vessels may be unable to operate on their usual routes during the summer months,” he told Riviera Maritime Media.
“Normally you need a certain amount of space for the 360° steering of the azimuth thruster, with extra space between the bottom side of the vessel and the top side tunnel construction of the hull,” Mr Batten continued. “Also, with a low draught, because of the drag, it is less efficient to use a tunnel as you might with a conventional vessel.”
Veth Propulsion identified a solution, using smaller propeller diameters but maximising the available space and creating a small tunnel underneath sleek gondolas for every azimuth thruster, to achieve the same effect and benefits.
“The hull resistance is much lower than vessels using a tunnel, to be able to sail on low draught,” Mr Batten explained, using as an example propulsion on inland tank barges Oranje Nassau V and Oranje Nassau VI.
“Working with our naval architect and the project’s naval architects, the aft hull was designed so that it was capable of sailing at a very low draught,” Mr Batten continued.
“Most notably, three L-drives were each mounted inside gondola-shaped moldings, each with a shallow tunnel, thus enabling it to operate at a reduced resistance despite the smaller under-keel clearance.”
Veth and Twin Disc are increasingly working with naval architects on different newbuilding projects, often to optimise the stern section. “We provide drawings in Autocad or 3D for the naval architects so they can easily incorporate our products in their design,” said Mr Batten.
“We prefer to be involved in the process as early as possible to discuss how the vessel will operate, for product selection and system configuration, etc. We would like to be viewed as a partner in the project rather than just a supplier.”
These collaborations become more important when vessels are built for specific missions and require exacting propulsion systems rather than relying on conventional shaftline configurations.
“There is no one-size-fits-all,” Mr Batten explains. “Now more than ever it is important to have this type of conversation with propulsion suppliers earlier in the design process and to select a partner that will guide and work with you along the way.”
Hybrid propulsion developments
Collaboration is also becoming more essential as vessels are built to meet tougher environmental regulations and requirements.
“It is wise for vessel owners operating in these areas to consider hybrid electric propulsion to ensure compliance,” said Mr Batten. “It is also important to understand how the vessel will operate and what type of propulsion system suits the mission.” These should include lifecycle-cost calculations and total cost of ownership considerations.
Veth developed a compact hybrid thruster with two permanent electric motors fitted on the aft side of the gearbox for vessels driven by both diesel and electric.
“These short e-motors contribute to a very small footprint of the thruster,” said Mr Batten. “The e-motors can also be used as generators to charge the batteries when running on the diesel engine.”
Its marine control drive, a free-standing slipping clutch used in thruster propulsion systems, has a power take in (PTI) specifically designed to be used for electric propulsion. “Either of these options are suitable for tugs and offshore support vessels. We are also on the forefront of electric propulsion with fully integrated and semi-integrated electrical L-drive thrusters that allows designers to utilise more below-deck space for other uses,” said Mr Batten.
Twin Disc developed its Master Clutch product line for parallel hybrid propulsion on vessels with a conventional shaft line or vessels using propulsion systems with reversing transmissions.
“The transmission has a PTI on the back of the primary shaft for an e-motor input, and power is transmitted to the propeller shaft via the standard forward and reverse clutches, allowing for standard transmission modes of operation,” Mr Batten explained.
“An integrated clutch is mounted between the diesel engine and the input of transmission that allows the vessel to operate in electric mode without back-driving the engine,” he continued.
“In addition to being able to operate in diesel, electric and boost mode (diesel and electric together), this arrangement allows the e-motors to be generators whenever the diesel is running, even during idle with the transmission in neutral.”
For serial hybrid or diesel electric propulsion on vessels with a conventional shaft line, Twin Disc developed reduction gearboxes based on proven marine transmission designs.
“These provide reduction for the electric motor speed to match the propeller speed requirement,” said Mr Batten. “This allows the selection of standard speed electric motors with the advantages of smaller size and lower capital expenditure.”
Propulsion technology and hybrid systems will be discussed and presented during Riviera’s series of Webinar Weeks and virtual conferences during 2021 - use this link to access details and register for these events