Are Swath platforms the ideal superyacht design?

21 January 2015By Amanda McCracken
Abeking and Rasmussen’s vision of its SWATH private superyacht in action.

The design of a SWATH is as extraordinary as its initials imply and may not mean much to you even when spelt out: Small Waterplane Area Twin Hull. But it could be the next design phenomenon to be taken up by clients who seek ever-increasing comfort and volume for their homes on the sea – a new style of expedition vessel, if you like.

The evidence comes from discussions with Till von Krause of Abeking & Rasmussen (A&R), which builds SWATHs for commercial applications, and Andrew Langton of Reymond Langton Design. Together they have been working on developing a 62m SWATH with interior volumes equivalent to that of an 80m monohull, for clients whose demands include travel in extreme comfort, staying at anchor on a stable platform in almost any weather conditions, use of an on-board helipad for guests and limousine tenders for ship-to-shore transfers.

To give you some idea of what a private SWATH looks like we take you back to an article on the 41m Silver Cloud (Boat International, April 2009) the first to be built at A&R for her American owners Alex and Renate Dreyfoos. They say it causes quite a stir wherever she goes. In just two years they have covered thousands of sea miles on board, encountering some nasty weather systems along the way that would normally have kept them in port – but such is the construction of these vessels that weather patterns are no longer a problem.

Extraordinarily, before the couple took delivery of Silver Cloud they were in danger of having to hang up their logbook and abort adventurous plans because of the oldest on-board affliction: seasickness. Even zero speed stabilisers on their previous yachts did not give enough stability in a swell and it soon became apparent that a monohull, however well-built, was not going to work. Alex Dreyfoos used his engineering skills alongside the expertise of A&R, and the result is a perfect cruising vessel for all weathers – and such is its stability that seasickness is no longer an issue.

Elbe is a commercial pilot Swath: spot the difference between this and a private SWATH.

What is a SWATH?

SWATH is an innovative hull concept for smooth service in rough seas. The idea was taken from the principle of semi-submersible offshore rigs, designed to provide a working platform with minimised motion in open sea.

The origins of a SWATH concept date back to the early 20th century but it was 1946 before a Canadian, Frederick Creed, was able to take out a British patent on his version. The US Navy became interested and carried out extensive design and test work in Hawaii, from which Dr Tom Lang obtained a patent for a Swath with additional stabilising fins. Just as importantly, the navy put a massive effort into design software, which later became available to purchase.

‘Without computer-aided design, a practical SWATH would hardly be possible,’ explains A&R’s technical director, Dr Klaas Spethmann.

The buoyancy of a SWATH ship is provided by its submerged torpedo-like bodies, connected by single or twin struts to the upper platform. The cross-section at sea surface level is minimised so very little of the vessel is exposed to the lifting forces of the waves. Abeking & Rasmussen has developed SWATH technology over the past 15 years, on the back of its long-standing experience in hydrodynamics, lightweight construction, special materials and leading-edge ship design.

With the know-how gained from full-scale service data of reference ships and special software tools A&R is now in a position to design and deliver SWATH ships under the brand name Swath@A&R.

SWATH vessels – such as the Silver Cloud private yacht – use outriggers to improve stability.

The new generation

With the demands from potential clients for designers to provide ever-increasing volumes for guests, technical spaces and crew aboard superyachts it made sense to look at how these vessels can be adapted even further to deliver unsurpassed luxury living to include the integration of such items as a helicopter, submarine and toys carried on board, instead of using a mothership.

Some sceptics will disagree, of course: the design of the commercial SWATH is less than pretty, with a cumbersome Lego-like structure atop a flat base, mounted on what looks like a submarine-type structure to each side of a very prominent girth. It spans almost the same width as the length, with struts to hold the ship above the waves.

So why go for a SWATH? The keys are volume and stability, and for those that get seasick, it’s a revelation. We went aboard a 50m SWATH vessel at Cuxhaven in Germany that is used as a floating hotel for pilots working out at sea; she stays offshore 365 days a year. The technical spaces are incredible, cavernous even. The torpedo-style bulbs attached to the platform can swallow up to four engines (diesel electric propulsion gives the choice of operating at a greater range of speeds), generators, complete crew areas, storage spaces with incredible headroom, and because they are separate from the living quarters, vibration can be significantly reduced compared to a monohull.

SWATH@A&R vessels have huge volumes available for technical spaces, living areas and toys storage

The motionless ride is due to the fact that the vessel has almost no waterplane area that can be lifted by a wave. It gives the vessel horizontal stability in some of the worst weather, keeping it riding the seas with near zero roll and a very slow pitching motion over large waves.

Andrew Langton has been fascinated by alternative watercraft such as hydrofoils, cats, trimarans, and SWATHs since his university days, so when von Krause asked him to develop a SWATH superyacht, he jumped at the chance.

‘The SWATH concept is a huge platform that enables us to create just about any form of superstructure we like; the only limits are the overall weight of the vessel and the distribution of that weight,’ he says. ‘A&R gave us freedom to come up with a new concept. The buoyancy of the SWATH is set out in such a way that we need to have the superstructure much further forward than on a monohull. Our concept for the SWATH was to create the volume of an 80m-plus yacht inside a 62m vessel; the layout of the interior spaces had to be considered at the same time we were creating the exterior look.

‘As this vessel is radically different from a monohull superyacht, a different look was more appropriate than to make it look like a conventional yacht. The front of the superstructure is almost vertical and almost entirely glass, giving the accommodation panoramic, unobstructed views of the ocean, with floor to ceiling windows and access to private terraces for the owner and guests. From this very strong design aesthetic the superstructure tapers dramatically aft, which eliminates the boxy look of the commercial vessels and helps limit the weight distribution.

‘As the SWATH has effectively four hulls – a pair of submerged torpedo tubes and the struts penetrating the water surface – this gives you the feeling of flying above the water.

‘We integrated the huge platform into the superstructure to make the vessel look like one form, whereas the commercial Swath looks like a platform with a house on top.’

A render of SWATH@A&R’s proposed private SWATH yacht

The volume Langton has created is so much more than on a large yacht, so had to be approached differently. Considering the rooms in a large monohull, Langton arranged them over four decks, keeping the stairways and lifts in the centre. One important area is the private owner’s deck with panoramic views and terraces all around.

The guest accommodation is designed looking forward with views to the sea, with the living spaces toward the aft decks. The huge windowless void underneath a commercial SWATH has been turned into a cinema, gym and spa area with sections of glass flooring.

‘The design connotations are endless,’ continues Langton, ‘with the only limit being weight. You can think out of the box with a SWATH and get creative.

‘We were already thinking about an observation room in the front of the torpedo hull, glass floor sections between the hulls, a helicopter pad, and we have planned a beach platform that drops from the main deck aft to the sea with a connecting staircase. It is even possible to integrate a paddle tennis court on main deck…

A comparison of the waterline area of a monohull, catamaran and SWATH hull.

‘The most challenging part of the design is that the platform of the SWATH is a huge ungainly rectangle and we had to work around this to create a form that would pass as a superyacht and not look like a box.

‘The incredible beam also means that a fully certified helipad is easily achieved. Landing a helicopter is safer as the SWATH will not be rolling around like a monohull can do.

‘The main tenders are located on a lower section of the main deck aft. They are launched overboard to the stern by an overhead ‘A’ frame davit/crane integrated into the styling of the superstructure. The tenders can be launched and retrieved very quickly and safely even on the move – even with guests on board if they are feeling brave!’

The superstructure is radically different from Silver Cloud’s clean and simple lines. Langton felt he could more radical in his design of Abeking and Rasmussen’s private SWATH because there are no real limits. With his creativity, a blank canvas and ideas of what prospective clients want, he concludes, ‘You have to recognise this vessel as a superyacht, whilst appearing refreshingly different to conventional yachts.’

The one burning question is how much it costs to build a SWATH compared to a monohull superyacht. Till von Krause has an answer: ‘If you look at the comparable volume, it is about 10 per cent more than a monohull, but the interior is very similar.’

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