Hush hush: How yacht owners are enjoying the sound of silence

15 January 2021

Today’s buyers are increasingly demanding when it comes to reducing noise on board – but just what is possible?  Charlotte Hogarth-Jones takes sound advice from industry experts

Speak to any yacht builder, or designer, and the story’s the same. “A term we’re hearing more and more from owners’ representatives is that their client is ‘allergic to noise’,” says Willem Jan van Cappellen. He’s the co-founder of Van Cappellen Consultancy, which works with independent clients as well as the likes of Feadship, Lürssen and Oceanco on sound projects for particularly large yachts. “At first, noise was just part of the building specs. It was a case of  ‘let’s put some numbers in there that sound reasonable, that will give us a reasonably quiet boat’,” he says. “But in some of today’s projects, it’s one of the most important parameters.”

In fact, the company has worked on several yachts in the past year and a half, “all incredibly large, two of which were Feadships”, that Van Cappellen would consider “right at the limit of what’s actually possible”. One of them was a 110 metre which ended up with decibel levels measuring around the 30s or 40s – even directly above the engine room.

Heesen worked closely with Rolls-Royce on the in-build Project Cosmos (above and below) to address cavitation issues around the propeller design to reduce noise

Often, this fixation on noise stems from owners who’ve been burned in the past: poor experiences on charter yachts, for example, or a current yacht with less sophisticated technology that’s been grating on them for the best part of a decade. “One particular owner came to us with his 15-year-old boat and said: ‘I can hear exactly which specific generator, on which side of the boat, is running when I try to sleep at night in my master cabin,’” laughs Marnix Hoekstra, co-director of Dutch design studio Vripack. “When it came to designing his new yacht, we went down to crazily low noise levels.”

It’s becoming more common for owners to bring their own independent acoustic consultant to the table, while shipyards such as Lürssen have a dedicated acoustic department. Much more is possible today owing to technological advancements across the board – from propellers through to air-conditioning systems – and one of the things that’s had the most significant impact, says Bart Bouwhuis, also co-director at Vripack, is the ability of consultants to calculate noise.

“In the very old days it was guessing really,” he says. “We’d just add in more and more insulation until the boat was quiet. Now you can calculate, and then specify, and then calculate again to look at what effect that had. That’s really helped to push things forward.”

And, if you’ve got a louder yacht, it might also be affecting you in more ways than you think. Professor Barry Smith, who founded the Centre for the Study of the Senses at the University of London and consulted for Heesen on their 50-metre yacht Home, has done significant research into how noise affects us. “The senses modify one another; there’s a lot of cross talk,” he explains. “So there are odours in shampoo that make your hair feel softer, for example, and in the same way sound can also have a very destructive effect on the way you taste things. It reduces your sense of salt, sweet and sour by about 10 to 15 per cent.” If you’re not convinced, he says, try eating on board a plane with white noise blaring in your ears, and then try again with noise-cancelling headphones. You’ll find your food tastes better, and the same is true on board your yacht. That perfectly cooked eggs benedict and freshly squeezed orange juice as you leave the harbour might not taste as delicious if there’s something buzzing in your ear.

But how loud is too loud? As a scale of reference, 49 decibels is roughly the sound of gently falling rain. At around 89 decibels, you’ll start to notice it and feel a bit uncomfortable – that’s the same level as white noise. And when you reach 120 decibels, it will start to feel pretty unpleasant. That is the same level as the scream of an F1 car going around Monaco, which used to be an unbelievably loud 145dB.

So what can be done if you want to make your next yacht super-silent, or improve conditions on board your current boat? One thing’s for sure, we’ve reached the pinnacle of what can be done with insulation, and experts are no longer focusing their efforts here. As Mark Cavendish, Heesen’s director of sales and marketing, puts it: “It’s a trade-off between what’s acceptable and what’s practical, and I think owners would get irritated by the impact on the loss of internal volume if you started applying more substantial quantities than we use currently.”

Home was the first Heesen to feature hybrid propulsion, with a super-quiet diesel-electric mode
Credit: Jeff Brown

How we use insulation may be getting more sophisticated, but there’s a general feeling that it’s just a Band-Aid masking a larger problem. As Bouwhuis puts it: “You buy an engine, which costs money, and then you buy insulation to solve the problem which you created! It’s kind of a negative spiral. And now we’re starting to question that.”

For many, the answer lies in battery power. Systems where the yacht’s “hotel load” can be run off batteries are a simple and increasingly common solution for those in search of peace.

The new Magellano 25 by Azimut is a good example of this. Owners can choose to include an optional “hotel mode” that promises zero emissions and absolute silence when the yacht is stationary. With the engines and generators off, the batteries will power the hotel load so there’s no low-grade rumble or fumes when you find that idyllic anchorage. Depending on the owner’s needs, consumption can be moderated by activating only compulsory utilities – the lower the consumption, the longer it will operate as “zero emissions”. The system can last about four-to-six hours during the day, and six-to-eight hours at night.

Heesen, meanwhile, is installing a much bigger battery bank on 80-metre Cosmos, which is in build. The batteries are charged by the generators, and the idea is that the yacht will be able to run fully quiet under their power for short periods of time, while also operating the yacht’s hotel load. Vripack also employed a battery system on a refit of a 70-metre yacht two years ago, for an owner who was particularly disturbed by noise, vibrations and odours coming from the generators, during lunch and dinner. The replaceable, hidden-away bank can now be activated whenever the owner desires.

The Azimut Magellano 25 Metri
Credit: Vincenzo De Cotiis

Of course, batteries aren’t the dream solution we might like them to be. “There’s a big trade-off,” says Cavendish. “Batteries are big, bulky, heavy, and are they ecologically viable? I don’t think they are.” Alternative fuel cells might be the answer, he suggests, citing a 13-metre sailing yacht he saw recently that used a methane fuel cell to produce 12V DC power. “The by-product of this thing was a bit of heat and pure water,” he says. “If you could scale that thing up, it’d be pretty awesome.”

Vripack is also looking at alternatives to the standard lithium-ion batteries, for a special 60-metre luxury yacht project that it’s calling Project 0. The owners have requested a 100 per cent fossil-fuel-free-yacht – no mean feat – and Vripack is in the research and development phase of the project. It has teamed up with nearby start-up Suwotec and they are investigating a bio-based battery that makes use of graphene, salt, leaves and sand. When you’re done with the battery, you simply walk up the beach and empty it. And, because it’s not solid-state, it can be made into any shape desired – it could be poured into a keel, for example.

But with the noise advantages of batteries, it’s no surprise that owners are turning to hybrid propulsion systems more and more. “We’re seeing a real demand for those systems, and the reason has to be noise, because you basically don’t get your money back,” says Christopher Swanhart of DLBA Naval Architects in Virginia. “We’ve done the sums and most often you save on fuel, but the systems are so expensive that you’re lucky if you break even.”

Heesen’s Project Electra, now Amare II, can cruise silently at 9 knots in electric mode

On the 110-metre Feadship mentioned by Van Cappellen earlier, a diesel-electric propulsion system was “a very significant factor” in reducing the noise. “What we did was design a good, solid foundation for the generator sets and put them on very soft mounts,” says Van Cappellen.

Heesen’s Home has a hybrid propulsion system, which registered decibel levels of around 46dB when the batteries were activated. And its new 50-metre yacht Amare II also operates a diesel-electric system, with the engines off up to about 10 knots. “Essentially then you’re back to that at-anchor harbour mode with just the generators running,” says Cavendish, “and they benefit from being in their own sound cocoon boxes, so you get a double hit on noise and vibration running under generators alone. It’s a fantastic system for keeping noise down.”

If you’re not about to invest in a new hybrid yacht, however, all is not lost. There are lots of ways to make improvements on board. The propeller design, for example, can have a significant impact, according to Van Cappellen. “Shipyards typically choose a propeller manufacturer that they’ve worked with before, but on another Feadship we worked on recently, for an American client who wanted a very silent boat, several manufacturers were consulted to see who came up with the best proposal.”

If your yacht’s louder than you’d like, “investigate what the source of the noise is, otherwise you’re just throwing money at it blindfolded”, he says. “It’s probably the propeller or the exhaust. People typically think, OK, let’s look at dampening treatments, acoustic carpet underlay… but we always say: if you want the biggest bang for your buck, just design and manufacture new propellers, and you’ll see the world of difference.” With €20,000 of refit material, you might achieve a noise reduction of around 2dB, but with a new propeller and docking – admittedly, more costly – the drop could be in excess of 10dB, resulting in a much more noticeable difference. Supported decks that hang off the main structure are also worth looking at, says Swanhart. “It’s not new,” he explains, “but it’s not cheap, so it’s not common”.

And there are some problems that are just a bit of a catch-22. Flushing toilets, notes Van Cappellen, are one of the most frequent complaints, and there’s little that can be done – although the company is currently doing a lot of research on them. “At the moment you can decouple all the pipes from the structure and insulate them individually,” he says, “but it’s kind of funny, because how far can we take this?” he laughs. You can’t, of course, stop people from needing the bathroom.

Noise from air-conditioning vents is another pet peeve. The sound of air being forced through a small space is what makes the din, and if you make the grilles in the cabins bigger, the noise will instantly drop. The problem, says Cavendish, is that if you make the grilles bigger and bigger, “eventually someone will say, god, those things are bloody ugly, can’t you make them smaller?” As is often the case, there are sacrifices to be made – be it space, cost or aesthetics – in the pursuit of total silence.

It’s also worth noting that the quieter your yacht becomes, the more new sounds appear. “The wind from outside, the noise travelling through a porthole, the compressor from a fridge in the room next door,” says Bouwhuis. Too much quiet can actually be unnerving. “When we worked on Axantha II and went into the wet room, the bathroom and the toilet, it was actually too silent,” says Hoekstra. “Because you didn’t have any windows it was very disturbing. You don’t want that, actually.”

Bart Bouwhuis, of Vripack, found that parts of 43-metre explorer Axantha II, now called Sea Eagle, were “actually too silent”

In fact, says Professor Smith, there’s a reason why we find totally quiet spaces a little unnerving. “What’s happening is that the brain is looking for signals,” he explains. “When it’s so quiet that it can’t find any signals, it starts to do the opposite and send this message backwards, down to the ear from the brain, almost as if to say, ‘hey what’s going on here, I’m not getting anything’, and sometimes it makes its own sounds to fill the void. This is why we have tinnitus, because the brain is filling in sounds which are not coming from our external environment, and also why you hear those tales of sailors hearing sinister voices during gales at sea.”

Instead, the aim in any project should be to swap unpleasant noises – generators, engines and the like – for those that are far more agreeable. “Owners don’t mind the sound of water splashing against a hull,” says Hoekstra, “but they want that, not the sound of mechanical systems.”

The right sounds, observes Professor Smith, can actually enhance our experience on board, whether it’s the ting-tinging of a sail against a mast, or the sound of seagulls up above. “I always point out the Provençal rosé paradox,” he says. “You can be sitting on your boat in Nice or Saint-Tropez, lifting this delicate pink bottle out of the ice bucket, with the sun on your face and joined by your companion, and you think, this is the most delicious rosé I’ve ever had. Then you try it somewhere else and you think, this is just OK, and it’s because you’re missing all those accompaniments that also gave you pleasure.”

In any event, notes Van Cappellen, “we’re now at the level where a very large yacht, moving at 15 or 16 knots, has the noise levels of a very quiet library”. Owners shouldn’t think that “the sky’s the limit”, he says, “because we’re beginning to reach the end of just what is possible."