Review- Silent 55, the extraordinary solar powered yacht ... · There is a slow, silent revolution under way in the yachting world. It is a revolution It is a revolution that is introducing

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Review: Silent 55, the extraordinary solarpowered yacht

Silent Yachts is tapping into the solar zeitgeist and creating a new meaning for theSilent Yachts is tapping into the solar zeitgeist and creating a new meaning for theterm ‘powercat’. Sam Fortescue reportsterm ‘powercat’. Sam Fortescue reports

There is a slow, silent revolution under way in the yachting world. It is a revolutionthat is introducing tonnes of lithium and a sprinkling of silicon to the spec list of newboats. Holding out the promise of silent mobility, plus limitless domestic power on

Yachting World(https://www.yachtingworld.com/author/yachJanuary 18, 2019

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board, it made a big splash at the last Cannes Festival of Yachting – not least thanksto the new Silent 55 catamaran which debuted there.

From the pontoon side, the Silent 55 looks like a typical modern catamaran, with abig coachroof studded with windows and a �ybridge helm. Except there’s no mast.Now, bear with me here. I realise that this is a sailing magazine, but we will shortlyget back to more familiar territory. The unique qualities of this catamaran onlybecome apparent from up top, where an expanse of solar panels stretches away foreand aft, embedded into the coachroof. The hard top itself carries yet more panels,and can be folded down �ush to give an unshaded solar array of 49m2. During theheat of a summer day in the Med, this is capable of generating 10kW of power andup to around 60kWh in the course of the day.

“The boat’s house load is 5-10kWh per day,” explains Jean-Marc Zanni, whodesigned the 55’s electrical system using 140kWh of Panasonic batteries and the370W Sunpower panels. “So you can go for weeks between recharging. The aim is toprovide full comfort and silence at anchor or in port.” It’s an intriguing possibility, and one that founder Michael Köhler is betting will appealto a broad constituency of sailors. He has spent �ve years honing the concept of thesolar-powered boat after he and his wife Heike �nally sold the monohull in whichthey had sailed tens of thousands of miles. “We were annoyed by the fact that on aconventional sailing boat, you are usually motoring 50% of the time,” he explains.“And the whole energy system can’t supply all the boat’s consumption withoutrunning the generator.” With insight gathered from years at sea, Köhler set about researching the best waysof harnessing renewable power aboard a cruising boat to keep the generator off. Heweighed up wind, solar and hydrogenation (where the speed of the water �owingover the prop when the boat is sailing turns an electric motor to generate power). “When you hear the wind turbine making all that noise, you think it will be producinglots of power,” he says. “But it’s not. When we did the measurements, solar producedmuch more.” The same is true of hydrogeneration using the main prop. “Regenerationstarts making sense at 10 knots of boat speed. Before that, it is not as good as itseems.” In fact, Silent Yachts doesn’t include the contribution of regeneration at all inits power equation. “The simple truth is that solar is by far the most effective.”

But to make a solar system work in reality, Köhler had to go back to the drawingboard on yacht design. The saloon and hulls have extra thermal insulation to keepair-con losses down, and the use of carbon and aramid in key areas helps reduce theoverall weight to a decent 17 tonnes (a Lagoon 52 weighs 22.5 tonnes). He has triedto keep windows out of the direct sun with long overhangs and in contrast to theLagoon’s 12 deck hatches, the Silent 55 has just two.

Holistic designOn the other hand, it has lots of opening windows, to allow a natural draught to doits job. “It’s a holistic approach – you can’t take the batteries and the drivetrain anddrop it into another boat.”

Of course, using the propulsion system quickly takes its toll of the boat’s 140kWbattery bank. The model on display at Cannes had two 135kW motors, giving youjust half an hour of silent motoring �at-out, albeit at a top speed of over 20 knots.More reasonable 30kW engines and a single-digit speed give you greater range. Nonetheless, the electric drive alone isn’t going to allow you to outrun a storm, or racehome after a day at anchor, so the boat is designed to work with a generator hiddenin the heavily insulated transom of its starboard hull. At cruising speed of around 5-6knots, Köhler says there is rarely any need to use the generator, citing an owner who

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has just emailed him triumphantly about a second year totally generator-free. “In theend, you have to compare it to the performance of a sailing boat,” Köhler says. “It isas fast as a sailing boat in similar conditions – after all, there is no wind without sun.” He went so far as to tell me during the sea trial in Palma, Mallorca, that he believedthe majority of sailors would happily dispense with the hassle of sails and a rig if onlythey could enjoy silent motoring and anchoring. “As soon as people realise theincredible concept of this boat, they won’t understand why they ever did anythingelse.”

The market does not seem to agree with him – yet. Sales of the boat have been good – they have already sold six, �ve of which arealready in the water. But of those, four customers have taken the sail option, whichmeans planting a 19.7m tall mast complete with boom and rigging slap bang in themiddle of the coachroof solar array. “I was a bit amazed,” Köhler admits. “The shadefrom the rig reduces the energy generated by the solar area, while it costs more andis heavier, so consumes more fuel. Maybe it is for optical reasons.” In fact, the shade of the rig slashes the average yield of the solar panels in half. In theMed, that means around 30kWh per day. But perhaps it �gures. The typical pro�le ofbuyers is an environmentalist who has a Tesla electric car and is “an early adopterwho likes to have things before others”. And at low speeds, with modest use of theair-con, the reduced energy generation should still cover daily consumption.

Under sail

The performance under sail should be reasonable because of the lightweight build ofthe boat, its broad 8.47m beam and stub keels added to each hull. Control lines areled back via conduits in the coachroof to the �ybridge helm station, to make single-handing under sail a possibility.

More interesting, I think, is a sort of halfway-house option using a kite rig. Thisoptimises the performance of the solar panels and gives plenty of propulsion. On thesmaller 55 and the 64, Silent Yachts currently recommends a 19m2 kite that costsaround €25,000 – a fraction of the cost of a new mast, boom, shrouds and sails. “Thesail automatically makes a �gure of eight above the boat, and you can steer it with ajoystick or an app on an android phone,” Köhler explains. “It can propel the 55 at upto 6 knots, even in light winds.” Perfect for an Atlantic crossing, then.

For the bigger Silent 79, which will hit the water in the summer, a commercial gradeSky Sail system needs to be used – a smaller version of the ones used on cargo ships.This kite can propel the boat at ten knots, but it costs more than ten times as much asits smaller cousin. Both are capable of pulling the boat upwind. So far, so new. But outside the novel energy and propulsion system, the Silent 55aims to do what many other cruising catamarans are trying to achieve. “Most of ourclients order for circumnavigation and long-term cruising,” Köhler says. So the boat isaimed to be as comfortable and capable as possible with watermakers, TVs and aninduction hob that all capitalise on the boat’s abundant energy. A �exible con�guration allows owners the choice of between three and six cabins –the latter designed for charter. The owner’s cabin lies forward of the saloon, underthe windows of the coachroof, which provide magni�cent views and abundantnatural light. There’s a walk-around bed and steps down into the starboard hull giveaccess to an en-suite shower room and heads.

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In my view, the best cabin lies aft of this, accessed in the traditional manner downsteps out of the saloon. The king-sized bed lies athwartships and the shower is largerthan that of the master cabin. There’s more space down here, better headroom andstill plenty of light courtesy of the many hull lights.

The �nish is good rather than spectacular, with a range of choices around woods andfabrics. The intention is to keep weight down by using laminate where possible, butowners can choose glass or porcelain �ttings wherever they want. The 37m2 saloon is the star attraction on this boat, offering copious amounts ofspace for a well-equipped galley, a comfy dining or lounging area and a fullyfunctional interior nav station.

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It connects through sliding doors to the broad, uncluttered cockpit, which offersseating and a dining table with room for eight. A 4.5m tender can be slung from theunderside of the bathing platform here, which can be raised and loweredhydraulically.There is more lounging space at the bow, where two little trampolinesbetween the nacelle and the hull make comfy, if eccentric, nests. There are alsocushions under the overhang of the coachroof.

On TrialWhen I had the chance to sea trial the Silent 55, albeit in motorboat format, I jumpedat it. It was a contrary autumn day on Mallorca with 15 knots breeze – just a shame,then, that this wasn’t one of the sailing con�gured versions.

To start with, getting on board is made really easy courtesy of deep boardingplatforms on the skirts. She feels rather square because of that vast, glazed saloonwith its deep overhang, and perhaps because of the utilitarian nature of the hard top,which is really about supporting more solar panels. Nevertheless, the side decks arebroad and uncluttered. The space up top is designed to concertina down �at, hence the hydraulic rams, fold-down seat back and lowering console. It makes a great sailing position, though, withall round visibility, and is also perfect for sundowners at anchor. When the rain comesdown, this feels quite exposed, but there is a fully sheltered helm at the front of thesaloon, and it is also possible to drive the boat from anywhere using a tablet thanksto smart electronics. Under power, the handling is superb. The quietness of the motors is astonishing, andI gather they’ll be inaudible on the next boat, which will do away with the gearbox.Even in the aft cabins, directly above the motors, there is no more than a distant hum.The boat responds instantly to the power and the wind seemed to have no impact atall. As with any propulsion system, the power consumption jumps as you pile on thespeed – it was sobering to see. At 6 knots, both motors drew 10kW but at 8 knots itwas closer to 30kW. I liked the huge saloon with its raised table for 360º views. And the sliding door andwindow gives great access aft, connecting the saloon and cockpit in �ne conditions.The �nish was smart and in muted tones, feeling more Scandinavian than German.

The futureIntriguingly, at least it seems to me, Köhler has tapped into something with theconcept behind Silent Yachts – but not entirely for the reasons that he expected.Buyers are opting for the sail or kite versions of the boat because they want acomfortable wind-powered craft with abundant, quiet energy on tap. It brings a whole new meaning to the term ‘powercat’

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Review- Silent 55, the extraordinary solar powered yacht ... · There is a slow, silent revolution under way in the yachting world. It is a revolution It is a revolution that is introducing