When upscaling works

Southern Wind Shipyard has been developing and evolving its own innovative construction techniques over the last 20 years, with 42 boats built (and counting) since the turn of the millennium…

What happens when the forensically detailed weight study for a grand prix racing yacht is scaled up and applied with equal rigour to a 100ft superyacht? You get a spreadsheet with more than 900 rows and 140 columns, with about 2,700 cells of live data that update in real time as the boat is designed, engineered and built, fitted out and rigged. Most superyacht builders don’t actually go to that level of detail in weight calculations, but at Southern Wind Shipyard they do.

In the last 20 years, Southern Wind has built many more composite sailing yachts in the 100ft (30m) size bracket than anyone else. With 42 boats launched since the turn of the millennium, all between 27m and 35m LOA, and every small detail from each of these projects meticulously logged, it all adds up to a vast quantity of data and a huge amount of boatbuilding experience.

‘We probably have the biggest library of weight calculations in our segment of the industry,’ says Marco Alberti, CEO of Southern Wind. If I select the SW96 Nyumba, for example and type in “galley basin”, it tells me the weight, the model, the location coordinates and the moment it generates longitudinally, transversally and vertically.’

‘An equivalent weight record for a raceboat won’t have anywhere near as much data because it has far fewer components,’ Alberti explains. ‘For us every tap, every battery, every drawer handle has to be recorded. And unlike a racing yacht build we also need to consider different loading scenarios. Trim has to be calculated at full sailing displacement and half load displacement as well as light ship displacement.’

The upshot is that despite the immense complexity of a Southern Wind yacht, the difference between its design weight and its actual displacement is around one per cent. And the huge library of weight calculations, from so many boats in the same size range, allows their design office to be very accurate in its estimates for future builds.

That’s just one of many reasons why Southern Wind has earned its first class reputation as a yacht builder. Another key factor is the exceptional quality of its composite construction.

Above and below: the carbon subfloor frames are fabricated in house

Over the last two decades the Southern Wind lamination team, led by composite maestro Stefan Falcon, has developed and gradually refined an exclusive technique for epoxy infusion to produce a laminate with far better technical properties than any other infusion method. Some of the details are trade secrets, but in essence it’s a three-shot process where the outer skin of the hull is vacuum-infused into a female mould and fully cured, then the core is bonded to it with structural epoxy adhesive (which is lighter than infusion resin). Finally, after the core bond is cured, the hull’s inner skin is infused on top.

Foam core for infusion is usually supplied as sheets with pre-cut slits, which make it easier to bend the material around the contours of a hull and also help to distribute the resin during the infusion process. ‘However, this adds hundreds of grams per square metre of extra resin,’ Falcon says, ‘and in the long term the grooves can increase the risk of print through when the hull is exposed to sunlight. To avoid these issues we have developed a technique that uses plain foam sheets instead of the typical cut ones. The foam sheets are individually cut to shape and pre-bent to exactly match the inner surface of the hull.’

Remarkable weight savings were achieved in the build of the SW105 GT Taniwha, which is the most performancefocused of the 105 mini-series

Andrea Micheli, Southern Wind CCO, explains that the shipyard’s vacuuminfused laminate has produced results that are close, in terms of quality and performance, to the high-end prepregs used in carbon spars and grand prix raceboat hulls, which need to be stored in a freezer and cured in an autoclave.

Micheli’s figures indicate that the resin-to-fabric ratio of prepreg laminate in a raceboat hull is typically 33-34 per cent; Southern Wind’s infusion technique delivers a ratio of 36-37 per cent at a much lower cost. These figures are far better than it’s possible to achieve with normal oneshot infusion, which also carries a much greater risk of dry spots in the laminate.

The SW ‘recipe’ includes threepart female hull moulds, modular cabin construction and composite structures

Quite sensibly for a shipyard whose ocean-going yachts are designed and built to last a lifetime, Southern Wind will only use foam cores rather than Nomex honeycomb between the outer and inner skins of its hulls. The weight saving of Nomex makes sense for boats that are stored ashore between races and tend to have a short competitive life. But the higher risk of delamination – which is inherent, because honeycomb has a far smaller surface area that can bond with the laminate than a sheet of foam – is unacceptable for a cruising yacht that spends much of its life bumping against docks, quays and tenders, and then has to stand up to the stresses and shock loads of hard ocean sailing.

There are applications where the combination of honeycomb core and prepreg laminate deliver a big weight saving benefit without any compromise in durability, such as bulkheads and decks, anchor lockers and lazarettes. The risk of delamination here is much lower and honeycomb core is exceptionally strong in compression, so for highly customised builds like the Reichel/Pugh designs Allsmoke and Morgana, and the Farr Yacht designs Sorceress and Taniwha, where performance is a higher priority than sound insulation, Southern Wind offers Nomex and prepreg carbon. And where ultimate strength is required in a solid laminate – rudder stock tubes, for example – autoclave-cured prepreg carbon is always used.

The three-part female hull moulds that are now widely used in large composite yacht construction were originally another Southern Wind innovation. The mould is initially built in one piece, from chipboard and plywood – low-cost materials with a small carbon footprint – with old resin that would otherwise have to be thrown away. After fairing and checking dimensions the mould is cut into three pieces that fit back together with a more perfect alignment than a CNC-produced three-part mould. ‘It was Stefan’s idea,’ Micheli recalls. ‘He presented it to Marco Alberti and they made a mock-up to explain the concept to Willy Persico, founder of Southern Wind. That model lived in the board room for years and was used in many meetings with clients.’

Quality assurance is taken well beyond the requirements of classification. Independent surveyors from QI Composites conduct non-destructive ultrasound testing (NDT) on each boat, two or three times during its build. On a typical visit they might check the bulkheads of one boat, the outer skin of another and the inner skin and deck of a third. ‘But we also conduct our own internal NDT checks on a weekly basis so that when we have a QI Composites check, this is mostly a formality,’ says Yann Dabbadie, SW technical manager, ‘and we ask the mast maker to do the same. All of the findings are compiled into a report that forms part of the owner’s manual so the client has complete visibility. We think this level of transparency is very important but it is absolutely not standard in the industry.’

After the hull is infused in a three-shot process, the internal structures are bonded in place. Nomex is used strategically

Inside the hull, the construction innovation continues. Cabins are built as modules on the factory floor, which is a much more efficient way to do it than building inside the hull. But while other yards tend to simply hoist finished modules straight into the boat and fix them in place, at Southern Wind they are taken apart after completion and then re-assembled on board. There are several reasons for this, Dabbadie explains. The modules can be built a lot lighter because they don’t need to support their own weight while being craned into the yacht. And because they are designed for disassembly, it’s easy to access everything behind and inside them – chainplates, systems, cables, pipework, the hull itself – for maintenance and repair.

The furniture is made from paper-cored panels that are very nearly as light as Nomex (which is an alternative on highly customised builds), and half the cost. These are set in solid timber and covered with carefully grain-matched veneer which the shipyard buys in rolls, rather than pre-bonded to plywood panels, to save a bit more weight.

Southern Wind’s main focus in recent years has been ‘smart custom’ builds, which are one of its unique selling points. The smart custom approach has been developed to offer most of the key advantages of a full custom build while eliminating most of the risks. In these projects the owner has almost complete freedom of choice for the internal layout and interior design (as well as the coachroof, cockpit, deck plan, rig and more), with just the constraints of a pre-designed and engineered hull.

There’s now an alternative to smart custom builds, although those will continue to be a mainstay of the yard’s production. The latest model, the 100X, is a semi-custom build where the owner selects from a wide range of pre-set options for layout, interior design and deck plan, rather than having complete free rein. The benefit for them is a faster, more efficient and sustainable build at a lower cost. And crucially – whichever way they choose to have their boat built – Southern Wind’s signature composite construction and build quality are exactly the same.

Click here for more information on Southern Wind Shipyard »