Battery power, new hull shapes and a focus on underwater noise are all helping to reduce noise and vibrations
Combating noise and vibrations on passenger ships has become ever-more effective – and a major way is through using battery power.
Using full battery and battery hybrid propulsion is rapidly growing and having a significant impact on cutting noise and vibration.
The fully electric e-ferry Ellen was delivered in Q3 this year to ferry operator ÆrøKommune, and besides the environmental effects, there have been strong benefits when it comes to noise and vibration.
ÆrøKommune information officer for renewable energy Halfdan Abrahamsen tells Passenger Ship Technology, “I am pleased to report it sails wonderfully. I’ve had the chance to sail with Ellen numerous times, both in better and worse weather conditions, and each time I have been pleased with the smooth sailing.”
He adds “Since the passenger deck is so close to the sea surface, passengers experience very little wave action. Also, the lack of significant vibrations is noticeable. You can still feel a slight mechanical effect from the drivetrain, which is bolted directly onto the hull, but it is very little in comparison to regular ferries, it is just a slight vibration, not a rumble. In the passenger salon, if you sit midships you can hear a whine from the drivetrain, but as you move up or down the salon, it is almost unnoticeable.”
He says the passenger salon is acoustically well designed and dampened, and that “you can have a normal conversation without problem, and you cannot hear what everyone else is talking about because of the acoustic dampening”.
Mr Abrahamsen says that passengers have expressed “over and over again how pleasant Ellen is to sail with”.
Comments posted on the ferry operator’s facebook page on the quality of the ride include (translated from Danish, from the page):
In the future, vibrations could theoretically be lowered even further. Mr Abrahamsen says “Like I said, the engines are bolted directly to the hull – possibly, with the right kind of dampeners between the engine and the hull, vibrations might be reduced to be unnoticeable. But that will be for some future designers to figure out. In any case, it is certainly significantly less than on a regular ferry.”
Hull shapes and low vibration
As electric drive technology has improved, quiet, low-vibration sailing has become an important marketing tool – but it is not always down to the drive system. Baleària’s third LNG-fuelled high-speed catamaran ferry, Eleanor Roosevelt, is to be launched on the Mediterranean in 2020. The Spanish shipping company worked with Australia’s Incat Crowther to come up with a next-generation shape that makes light work of the waves and keeps passengers in comfort.
According to Baleària, the 123-m hull features “behaviourial enhancements”, primarily in the form of a third central hull that houses a retractable T-foil. “The shape of the ship was specially designed to considerably reduce vertical acceleration for more comfortable journeys by lowering vibration and noise to unprecedentedly optimal levels,” the ferry company says.
Similarly, Ulstein’s X-Bow design is another example of how the shape of the hull can assist – or even exceed – the capacity of the driveline in cutting vibration and noise levels. The latest commission of an X-Bow ship, now running to more than 100, is for Lindblad Expeditions, working with National Geographic. The 124-m polar vessel will be launched in 2021.
As Ulstein says, the shape is the reverse of a conventional bow because it leans backwards instead of forwards. “An X-Bow vessel cleaves the waves, significantly reducing noise and vibration.” Also, not insignificantly in view of IMO regulations about providing a good working environment for crew, Ulstein says the design “is more comfortable for the crew,” mainly because there is much less slamming.
And sometimes it is not just the noise that passengers hear that driveline manufacturers must consider. In Ontario, Canada, Blue Heron Cruise’s latest ferry has been proving the value of a high-speed engine mounted on the equivalent of shock absorbers – pre-engineered rubber mounts designed to cut vibration and noise in Unesco-designated Bruce Peninsular. Here environmental restrictions are also measured in the decibels clocked by the local community living along the shore. The ferry can hit 40 knots.
Cutting underwater noise
Class interest in underwater noise has blossomed, with five class societies now including notations on this topic – Bureau Veritas, RINA, DNV GL, Lloyd’s Register and ABS.
Bureau Veritas (BV) introduced its class notation NR 614 – URN in 2014 and updated it in 2018. BV launched this voluntary notation to help ship operators and ship builders measure and reduce underwater radiated noise.
Commenting on the fact five class societies have now launched notations on the subject, BV head of measurement department Eric Baudin says “This is a good size, the industry is starting to acknowledge several different notations, maybe it would be good to harmonise and propose something that is coherent in regard to fauna. In the close future class societies may work on that.”
He singles out another reason that would push the uptake of such notations: two Canadian ports, Port of Vancouver and Prince Rupert have launched port tax reductions to reduce underwater noise due to the endangered South Resident Killer Whales off the cost of British Columbia.
Mr Baudin comments “Vancouver has set three voluntary speed reduction campaigns together with noise measurements and has published comprehensive reports. Canada itself is still very active in this area and has submitted several information papers to the IMO MEPC and organised several dedicated workshops.”
Mr Baudin says in January 2019, Canada organised a workshop at IMO on this topic, involving 150 people. “This looked at how to integrate technical aspects to move forward and set up guidelines for new regulations in the future. Interest is great enough to make this a short-term or medium-term issue,” notes Mr Baudin.
A challenge in reducing underwater noise is balancing this with energy efficiency. Mr Baudin says “There is a compromise between ship efficiency and the design towards underwater noise which might face some competition but would boost innovation, which was acknowledged at this workshop.
“There is a move for speed reduction, which means less noise from cavitation from the propeller, so this could be solution to the compromise between noise reduction, energy efficiency and gas emissions.”
The French Government has also issued a shared agreement involving ship operators that addresses pollution from ships to the ocean, where underwater noise has been specifically addressed. Nine French shipowners have already signed this agreement: Brittany Ferries, CMA CGM, Corsica Ferries, Corsica Linea, La Méridionale, Louis Dreyfus Armateurs, L’Express des îles, Orange Marine and Ponant.
Mr Baudin says “It is an active plan supported by Armateurs de France, the big shipping lines are saying let’s do it together and nine shipowners have signed the action plan and are working on main issues and proposing actions. Among the actions there is specifically an underwater noise and class notation related to this. This suggests that using a notation for your ship is a good option.”
Snapshot CV: Eric Baudin (Bureau Veritas)
Eric Baudin heads the onsite measurements section within the service department of Bureau Veritas Marine and Offshore, managing marine and offshore measurements-based activities from research and development projects to onsite assessment and technical assistance. He joined Bureau Veritas in 2000 as onsite measurement engineer. He graduated as a mechanical engineer from Conservatoire National des Arts et Métiers de Paris. Mr Baudin has managed several EU projects for BV, including two focusing on underwater noise: SILENV and AQUO. He joined the IMO workshop for underwater noise guidelines in 2013 and the initiative Racket in the Ocean in 2016.