Why these extreme multihull concepts could be the future of catamaran design

Holiday homes, restaurants, even cities may soon be coming to a quiet beach or harbour near you, reports Sam Fortescue

As boats become ever more like homes on water, something else is changing: designers and builders have been turning their attention to the market for floating buildings. New concepts to emerge range from a thatched beach cottage atop a catamaran hull to an entire floating city, generating its own food and power. The one thing they have in common is they’re movable structures that can be parked wherever they can drop the hook. And soon they could be coming to a peaceful estuary near you.

There is an opportunity here, of course, to create additional living and leisure space in areas where the land is already choked with people. Imagine being able to moor a temporary holiday village off Bournemouth Beach, for example, or create a restaurant off Dartmouth without affecting the townscape.

But the flip side of the coin is that someone could park a large floating structure right in front of your sea view, or occupy a quiet, sensitive environment. Imagine, as sailors, falling asleep in a deserted anchorage and waking up with a throbbing beach bar right next to us!

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Floating homes and docks are being designed to use Seafloatech’s eco-friendly anchoring system

“If a craft is movable and can drop an anchor, it would be classed as ‘any other vessel’ and would not need consent,” confirms Martin Willis, executive officer of the UK Harbour Masters’ Association. “But if it’s a commercial business, it’d be subject to the relevant regulation – there are no rights to come in and open a business in a harbour without the Harbour Master’s consent.” Alternatively, it may fall under MCA coding as a passenger craft.

In some parts of the world, floating structures are already quite common. Upscale luxury holiday resorts in Thailand or the Maldives, for example, offer floating villas. And soon you might expect to see whole floating marinas if you find yourself close to St Tropez. France’s recent move to protect crucial Neptune grass meadows in the Mediterranean means that anchoring off the town is severely limited for yachts over 24m.

To get round the problem, a company called Seafloattech has developed a system of screwing steel frames to the seabed to moor big structures on giant hydraulic shock absorbers. “We had a prototype size in place for six months in the Bay of St Tropez,” says managing director Lionel Péan, the French ocean racing star and past winner of the Whitbread Round the World Race. “It could accommodate up to 70 boats in a maximum wind of 42 knots, with up to 2.4m wave heights with no structural problems or injuries.”

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Offshore developments

The hydraulics keep the marina on station despite the tide and help to counteract wave action. It is even possible to use the system to tether a boat or a home through storm-force conditions, insists Pean. “If you want to build something to resist a typhoon, for instance, you have to make special arrangements with the customer. It can be done, but it costs a lot. In the Med, you don’t need 5-6m waves resistance.”

Seafloattech itself will ultimately just licence the tethering system, but it is working with partners who envisage all manner of structures atop their platforms. There are swimming pools, beach clubs, superyacht berths, hotels and villas.

“We believe that the demographic surge will force the coastal states to really focus on offshore coastline development,” adds Pean. “I am for a two-fold operation including sanctuary areas and social offshore development zones. We think that Northern Europe will take some more time but as soon as we have some units up and running, it will happen quickly.”

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Seafloattech has developed a steel tethering structure that is screwed to the seabed with hydraulic shock absorbers that can secure any number of floating homes. Standard versions can cope easily with Mediterranean weather conditions

Another French concern, Faréa, has taken a markedly different approach, developing a home that sits on two deep metal floats that also contain cabins. It is a simple catamaran, propelled by an outboard at the ‘stern’ and anchored with normal ground tackle at the ‘bow’. Navigation is slow and only for fine weather, but retractable centreboards mean it can be beached.

“They amount to 86m2 of space, with seven double cabins separate heads and bathroom and three terraces,” explains founder Christophe Roi. “They are self-sufficient in water and electricity, thanks to the oversized photovoltaic panels and fuel cells.”

A thatched roof multihull?

The original plan was for something more like a floating house, but feedback from insurers pushed Faréa towards a craft that meets category C of the Recreational Craft Directive. “It means they can stand up to Force 6 and 2m waves,” explains Roi. “What with rental prices so terribly high in England, I am certain that living on water should be a possibility.”

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Original Faréa concept was for an economical floating home with a thatched roof, but later versions can meet RCD Cat C

A fully equipped F2C model would cost around €160,000 to install, he adds. With the average Newquay home costing £730,000, according to RightMove, he has a good point.

Alva Yachts offers more architecturally ambitious 45m2 holiday homes with an infinity pool and a terrace. Not self-propelled, costs range from €85,000 to €200,000 depending on finish. The fledgling German company is using its founders’ experience of building catamarans that run on renewable power to offer low-carbon homes.

“The floating homes are literally super luxury yachts without propulsion,” explains co-founder Mathias May. “The hull and ‘sails’ are made of composites, while energy consumption, supply and distribution is comparable to a solar yacht. We strive to be as efficient as possible to get rid of diesel gensets in remote areas. It is no coincidence that our first customer for such a project comes from the Maldives.”

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This ocean resort features a number of Alva Yachts floating eco holiday homes costing from €85,000 to €200,000

Meanwhile, two Finnish companies have developed a series of even larger floating structures whose near-total self-sufficiency allows them to remain offshore indefinitely. Architects Sigge and builder AdMares have turned the world’s largest floating villa (all 6,000m2 of it) in Abu Dhabi into an autonomous boat capable of tackling waves up to 1.2m.

By fitting a wheelhouse and three Rolls Royce US 55 FP azimuth thrusters with a total 750kW output, the villa can move itself around the sheltered waters of the emirate. An anchoring system at each end of the platform is equipped with whopping 38mm chain and 1,575kg anchors.

Off nearby Qatar, the Finnish firms have been hard at work installing 16 floating hotels with a total of 1,616 rooms, aimed at providing temporary accommodation for the huge influx of football fans due for the 2022 World Cup. With four storeys including a lounging area and a restaurant, each hotel can simply be towed to a new location after the tournament. The only restriction is the 4m draught.

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This Oceanix concept sees hexagonal clusters of floating homes linking up to become towns with net zero emissions

Floating towns

Several orders of magnitude further up the scale and you reach floating towns. Some concepts, like Oceanix, are very serious attempts to expand the boundaries of human habitation to ‘the next frontier’. It is a consortium of companies focusing on the UN’s ‘New Urban Agenda’ with a plan to build homes on pods clustered in hexagons, in turn clustered into larger hexagons, and so on, up to cities of 10,000 people.

Their vision includes parks, arenas, restaurants, offices up to three stories high and built-in docking for solar-powered watercraft. Energy is harvested from waves, wind, sun as well as algae bioreactors and more to create a net-zero consumer, while food is grown on and under the city.

“We believe humanity can live in harmony with life below water – it is not a question of one versus the other,” says CEO Marc Collins Chen. “The technology exists for us to live on water, while nature continues to thrive under. Floating cities by design embrace all types of marine activities, so they are complementary to existing activities like fishing and sailing.”

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Nomadia is a multi-deck craft for 3,000 guests. An alternative to cruise ship holidays, it features an internal marina and even beaches

The initial sites envisaged for a city are all on the fringes of the Tropics, from Japan to Thailand, and the structures are designed to withstand Category 5 storms.

A more Eurocentric view comes from two designers of cities on boats. French naval architect Sylvain Viau has developed an outline for a triangular craft measuring 372m in length, with a jaw-dropping beam of 369m. Across 12 decks moving at up to 5 knots, some 3,000 guests can be accommodated, along with lecture halls, meeting rooms, restaurants, shops, manmade beaches and an internal marina capable of berthing ten 100ft yachts.

Fun and games afloat

These giant ‘craft’ are nothing to do with loving the sea or even respecting the enivronment. “People are not interested in the sea, they are interested in casinos, cinema, fun entertainment,” Chen explains. “In my imagination, you welcome everybody on board in a nice location. The platform doesn’t move during the season, only in the winter, when it’s time to find a new spot.”

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With yards promoting designs such as this BlackCat 50m, superyacht multihulls look set to be the next very big thing

At anchor, giant inlets like gills down each flank would channel waves into a generator to produce energy. And when it’s time to move, the boat raises its 300-tonne anchor and blows out its ballast tanks to reduce its draught from 20m to 11m.

Germany’s beiderbeck designs recently made headlines with the publication of a €500m concept catamaran called Galileo2, capable of berthing yachts up to 80m, and offering a fold-down restaurant and an open-air amphitheatre cinema. With a nod at managing greenhouse gas emissions, this small floating town would be powered by gigantic fuel cells, and would pioneer so-called marine thermal energy in yachting.

“You can use the temperature difference between the deeper and surface water,” explains Timo Hartmüller of beiderbeck. “Obviously, you need to be in deep water, but we designed the yacht to stow a 1km long hose on board.”

Some of these floating titans may never make it off the drawing board, particularly in view of the way that coronavirus has decimated the cruise ship industry. But the current is running hard towards extending communities above the waves, and whatever you may think of these concepts, be they luxury pads or modest holiday cabins, expect to see more of them coming to a stretch of coast near you.

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Mobile pontoon

Multimarine near Plymouth is nearing completion of a 108ft x 28ft motorised platform called the Gweek Pontoon, which the owner plans to charter out for use as a mobile regatta and watersports base.

It is fitted with an anchor and windlass, as well as three 200hp engines, and includes a built-in hydraulic slipway. It is built from foam-core vinylester laminate and carbon fibre for light weight and a trifling draught of just 100mm.

First published in the September 2020 issue of Yachting World.

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