Designers are listening to the underwater noise debate

Paul Gunton
Paul Gunton
ShipInsight

14 March 2019


Back in early February, I wrote about a technical workshop that focused on the effect of underwater noise on the marine environment. It took place in January at IMO’s headquarters in London and was organised by Transport Canada and its findings will be provided to the Marine Environment Protection Committee’s 74th meeting in May.

Since that workshop – perhaps because of it – ship noise has become a more common theme in engineers’ and shipowners’ plans. I have been prompted to revisit the topic because it made an appearance in the mainstream media in the UK, where the BBC carried a news item last week about research conducted in the waters around the UK, Ireland and western Europe. It resulted in the first map of this region that showed where shipping noise is particularly significant.

That news item relates to a 10-minute segment at the start of a regional TV programme that is available online until 2 April; it is only accessible in the UK.

That programme interviewed Dr Nathan Merchant, principal scientist and team leader for the Noise and Bioacoustics Team at a UK government agency, the Centre for Environment, Fisheries and Aquaculture Science. He told me yesterday (13 March) that a scientific paper is being prepared based on its research, which he expects will be published in August.

He had also spoken at the January workshop, where he said that as many as 130 marine species have so far been identified as being affected by underwater sound and his new study will complement the extensive work that has been done in western Canada and which was discussed at the workshop.

In that region, whales are particularly at risk from noise and action is being taken to encourage ships to reduce their noise – for example by slowing down – and to avoid sensitive areas. This enhanced concern in that region about noise is already having an effect: three weeks ago, we reported that Wärtsilä’s EnergoProFin propeller cap has been listed in Vancouver Fraser Port Authority’s EcoAction Program for 2019 in the ‘vessel quieting’ category because of the effect it has on reducing propeller cavitation.

As a result, ships fitted with the device will qualify for a 23% discount on harbour dues at the Port of Vancouver. That is quite a large chunk of change.

Two days after that news item was published, ferry operator Scandlines announced that it will replace all the thrusters on four hybrid ferries serving Puttgarden in Germany and Rødby in Denmark with new units that it says will produce less noise and vibration, thanks to the thrusters’ homogenous water flow. “The exchange lessens the environmental impact significantly,” its statement said, improving the conditions for harbour porpoises.

“Furthermore,” it went on, “easier water flow during propulsion ultimately reduces emissions, including CO2.” In all, 16 thrusters will be exchanged for Rolls-Royce Azipull units at a cost in excess of €13M, starting in Q3 this year.

They will, no doubt, also save fuel and money, although the statement does not discuss that, which is significant: Scandlines clearly decided to convey a wholly environmental message, with underwater noise trumping emissions as its headline-grabbing news hook.

While propellers are an obvious focus for noise-reducing efforts, a break-out group during the January workshop looked at other sources of machinery noise and what could be done about them. I took part in that discussion and heard some in the room suggest that podded systems are not necessarily quieter, especially those that have their motor inside the pod.

But much of our time was devoted to the fact that large two stroke engines, bolted to the hull, inevitably transfer noise through the hull into the surrounding water and it appears that very little work has been done towards understanding that process.

Leading our discussion was Kai Abahamsen, senior principal engineer at DNV GL and his summary report to the workshop reflected a point made by the engine manufacturers in our group: that two-stroke engines are chosen on the basis of their efficiency and economy, not their noise.

So there is little incentive for machinery OEMs or shipowners to invest in noise reduction and the group’s report suggested that some legal or economic incentives will be needed – such as the scheme offered in Vancouver. Mr Abahamsen had earlier told the group that Vancouver’s initiative was a factor in a significant boost in requests from passenger ship operators for DNV GL’s SILENT-E class notation.

One technology that our group did think had potential to reduce noise was air lubrication. It reduces hull resistance, and thus engine power and noise, but it also partially separates the hull and its vibrations from direct contact with the water. “That is really a very promising noise control measure to investigate further,” Mr Abahamsen said in his summing up.

I believe the workshop was an important event. It felt like the start of something significant; an event that will be remembered as the moment when something changed in our appreciation of the environmental impact of underwater noise and a determination to do something about it took hold. More important, though, is what has happened since: if the examples I have mentioned are signs of a new approach to ship design and engineering, I am proud to have been a small part in starting that process. I look forward to seeing how this is reflected in the workshop’s eventual report to MEPC 74.