Naval architects must collaborate with propulsion package specialists to optimise a vessel’s engines, generators, propellers or thrusters
A ship’s efficiency can be improved through integrated propulsion systems, designed from engine-to-wake. Naval architects must consider power requirements for a vessel’s operations, whether this is for voyage navigation, or tackling adverse weather and sea conditions, or operations such as dynamic positioning and towage. Designers should then bring in propulsion system providers to incorporate optimised propellers or thrusters and engines, or hybrid propulsion systems.
These were some of the aspects of ship design a panel of experts debated during Riviera’s Propulsion packages: the full package? Propulsion packages critically assessed webinar.
This webinar, sponsored by Berg Propulsion, was held on 26 February as part of the Marine Propulsion Webinar Week.
On the webinar panel were Berg Propulsion product director Emil Cerdier, Veth Propulsion product manager for thrusters Bastiaan van Zuijlekom, Servogear managing director Torleif Stokke and Saga Cruises Capt Kim Tanner.
Mr Cerdier said there are three areas central to vessel optimisation: product; system; and operational efficiencies. Product efficiency is about minimising mechanical and hydrodynamical losses.
“System efficiency is based on how to find the best combination of equipment for a specific application,” said Mr Cerdier, “and operation efficiency is about how to make sure operators use the benefits and possibilities of the technical solutions.”
Mr Cerdier said Berg Propulsion designs its products in collaboration with partners – vessel operators, yards, designers and suppliers.
“We also look at what our internal business needs are and what new technologies we can incorporate,” he said. “Based on this, our product definition team creates a requirement specification and hands over to engineering.”
In parallel with the design work, Berg Propulsion conducts computational verification studies using finite element modelling and fluid dynamics to check reliability and performance.
“The next step is a pilot build, where we verify the production process and run physical testing,” Mr Cerdier continued.
“After that we do a field follow installation with a customer where we follow the performance of the product and make necessary adjustments if needed.”
Mr Cerdier explained how Berg Propulsion had redeveloped the nozzle on one of its azimuth thrusters to improve efficiency.
“We studied the nozzle attachment system on our second-generation thruster and came up with improvements for generation three,” he said.
“These improvements led to an increased efficiency that means you reach 3% higher bollard pull with the same input power, or need 5% less power to reach the same bollard pull.”
These products should be linked within an integrated propulsion system on vessels, with engines optimised to generate the power required by propellers or thrusters. These can be supplemented by batteries, shaft alternators and booster motors in a hybrid system.
“It is very important to give an accurate picture of the pros and cons of different options,” said Mr Cerdier. Berg Propulsion offers its VesselCalc software for these comparisons.
An operator would input operational and contractual requirements, followed by the operational profile of the proposed vessel. This would include hours of operation per year and percentage of time the vessel is in each operation mode.
The next stage is to input the resistance data for the hull to give accurate performance predictions. The type and configuration of propulsion system is also inputted, including number and size of propellers, revolutions and input power.
“And lastly, you configure the power generation and conversion system,” said Mr Cerdier, “including the main engines, gensets, batteries, shaft alternators and booster motors.”
He continued: “The system will then produce a report, including the major factors for a comprehensive comparison between the optional configurations.”
Berg Propulsion used VesselCalc to develop propulsion design for a hybrid harbour tug. “It became clear that the lowered fuel consumption and maintenance cost resulted in a quick return of investment,” said Mr Cerdier.
“To reach efficient operations, the key is to look at all aspects,” he said. This includes the efficiency of operating these systems in different modes.
“The crew has a major impact on how fuel efficiently the vessel is being operated,” he continued. “Proper training is a key factor to leverage the incorporated design concepts.”
Mr Cerdier also thinks automated and active systems should be used to “continuously analyse the conditions and automatically adjusts to optimise efficiency.” Data from these could then be used for comparing propulsion performance across a fleet to increase efficiency and up-time.
Veth Propulsion’s Mr van Zuijlekom emphasised the benefits for vessel efficiency of involving propulsion manufacturers and integrators during ship design.
“We should be getting involved at the early stage in design and construction and finding out what customers and designers want,” he said. “We can provide flexible and efficient co-operation for system integration.”
Naval architects can use their knowledge and technology to provide more space on vessels for cargo and passengers. Or they can use propulsion technology to design shallow draught vessels.
By involving propulsion providers designers can “implement a comprehensive solution, a full package,” said Mr van Zuijlekom.
This involves adding value to the ship’s performance over its entire lifespan. “We give designers more freedom and flexibility, by saving space for cargo or passengers,” he said.
Veth offers two similar 550-kW rated propulsion drives in different designs. Its VL-550 is 3,500 mm tall, of which 2,450 mm is the drive motor. But its VL-550i is 1,600 mm tall with just a 410 mm high motor.
“We integrated the permanent magnet motor in the thruster top section,” said Mr van Zuijlekom. “This is an optimum-shape pod with no vulnerable motors or planetary gears under water.
“There are no sliprings, no main motor, flexibility in positioning, just one gearbox, and no high-frequency underwater noise and the permanent magnet motor has optimised rpm.”
These technologies reduce capital expenditure on the main engines and generators and provide solutions to ship design challenges. “Develop solutions instead of just propulsion,” said Mr van Zuijlekom. “Develop ships instead of just solutions.”
Servogear’s Mr Stokke commented on developments in electric-driven propulsion for high-speed vessels, such as fast ferries with hybrid propulsion, or those powered by batteries.
“We are looking into what is possible from using electric-power instead of conventional diesel in variable power ranges,” he said.
“An electric engine in combination with a gearbox gives reduced weight and reduced capital expenditure,” said Mr Stokke.
He thinks it is more cost-effective to improve the efficiency of the propulsion package than invest in batteries with more storage capabilities.
It could be better “to design a 15% more efficient propulsion system, rather than buying a 15% larger battery-package,” Mr Stokke said. “Focusing on the entire system, as well as components, gives reduced capital expenditure.”
“It is more cost-effective to improve the efficiency of the propulsion package than invest in batteries with more storage capabilities”
He offered examples of Servogear packages during his presentation, including High Speed Transfer (HST) Marine’s new high-speed crew transfer vessel HST Ella, a hybrid Chartwell 24 design. This will have Servogear transmission with two Catepillar C32 main diesel engines and two Danfoss generator motors. These will drive two propellers with integrated rudders for a top speed of 32 knots. “We can supply everything except the main engines,” said Mr Stokke.
Another example is Medstraum, an all-electric fast passenger vessel developed under the EU-funded TrAM(2021) project and equipped with Servogear.
“This will be an all-electric fast ferry to operator on batteries only,” he said. “It will charge 1.5 MWh batteries at dock and has a speed of 25 knots.” These batteries will feed two motors rated 550 kW at 1,380 rpm to drive two 1,375 mm-diameter propellers on a carbon-fibre bracket: “Weight is essential for high-speed vessels,” said Mr Stokke.
In a third example, Mr Stokke said Servogear was supplying the Hydrogen Viking retrofit project, which will involve replacing diesel generators on a superyacht. In this project, hydrogen fuel cells and batteries will be installed, powering two Danfoss EM-PMI540-T4000 motors. These will turn 1,075-mm diameter propellers through Servogear HDE 220 (2,95:1) gears. Hydrogen Viking could have a top speed of 35 knots.
The benefits of cruise ship podded propulsion
Podded azimuth propulsion provides huge advantages to cruise ship operations, but there are maintenance disadvantages.
Saga Cruises Capt Kim Tanner spoke about the benefits and challenges from a user perspective. He is a master on Saga Cruises newbuild cruise ships Spirit of Discovery and Spirit of Adventure. These have podded propulsors able to rotate 360-degrees for manoeuvring and docking.
“They provide more lateral movement for moving vessels alongside or getting into smaller ports,” said Capt Tanner. This means there are less requirements for employing tugboats to manoeuvre a cruise ship into port.
“There is potential for increasing the portfolio of harbours cruise ships can enter,” he continued. “There are also increased efficiencies, with less time spent performing each manoeuvre.”
Podded propulsion is also better for environmental aspects of cruise shipping. “Efficiencies lead to less generator run-time, they can be kept running at optimum speed,” said Capt Tanner.
There are also lower emissions, as fewer generators are required for electric propulsion compared to using main engines and conventional propellers.
“Pods create less noise and vibration, which equals less impact on sea life,” he said.
There are also advantages in ship design as there is more engineroom space, while layout benefits stem from propulsion motors being exterior to the vessel, with no long propeller shafts.
There are also “certain maintenance advantages, such as no pedestal bearings or common shaft alignment issues” said Capt Tanner. “All of this should inevitably lead to cost savings in the long run.”
However, podded propulsion comes with challenges to both newbuild projects and throughout the life of a cruise ship.
“Initial installation costs are normally greater than those of conventional drives,” said Capt Tanner. “There are elevated technical risks, as the arrangement of the electrical system is more complex.”
Additionally, pod maintenance often requires higher levels of preparation and expertise, and there can be a greater risk of system damage in case of seal leakage. There are also challenges with maintenance, as ships need to be taken to a dockyard for maintenance or replacement of podded azimuth thrusters if there are technical issues or damage.