At the NEC show in February 2014 The Swift Group launched two new ranges of caravans, right at the top end of the touring market. The Swift Elegance and Sterling Continental ooze luxury and style to an extent never before seen in a caravan from Swift.

But it's what's under the skin that makes these caravans really unique. The bodyshell is completely timberless, even the floor. There is no wood or plywood, or any product made from wood, in the bodyshell construction.

Five years ago Swift set itself the target of eliminating all timber and replacing it with modern materials that would not rot. Nothing made from wood was to survive, not even in areas that did not seem critical. The resulting caravan had to be extremely strong as well as durable. A second objective was to produce a caravan more aerodynamic than anything that had ever left the factory before.

The result is SMART HT, with HT standing for High Technology. It represents a significant advance on the SMART construction introduced by Swift for all models at the start of the 2014 model year. Some of the technology is truly groundbreaking, at least as far as touring caravans are concerned, with many elements filed by Swift for patent protection.

Eliminating wood from the upper bodyshell is relatively easy with today's technology and several European manufacturers, including Bailey of Bristol, have already done so. The timber framework can be replaced with components made from composite plastics or polyurethane and the internal plywood wallboard replaced with GRP or another form of plastic.

Swift had already chosen polyurethane for its strength and uniformity, along with the fact that it is completely impervious to water. It was introduced for all models at the start of the 2014 model year as part of the SMART construction methodology, which included a host of other refinements designed to improve the strength and durability of the bodyshell.

The next consideration was how to construct the side and roof panels. Swift decided to use a sandwich of GRP with expanded polystyrene insulation inside, strengthened with polyurethane struts. One advantage of this approach is that, by using the same facing material each side, the panel is balanced from a thermal point of view. This means it will not try to distort as the temperature changes.

GRP also has the advantage of being knock resistant and today it can be made to be just as shiny as painted aluminium. This is a positive benefit for the external skin but shiny walls are not so attractive inside the caravan. To get round this Swift worked with the supplier to arrange for a decorative finish to be embedded into the GRP. It's not unlike traditional papered wallboard in appearance but is tougher and easy to wipe clean.

cfd Computational Fluid Dynamics was used to hone the shape of the new caravans

If Swift was to achieve the goal of producing its most aerodynamic caravan to date is was clear that the front and rear body panels would need to be reshaped. It turned to Total Sim Ltd whose Computational Fluid Dynamics (CFD) software had already helped to hone the class leading Conqueror and Elite models, not to mention formula one racing cars, The result was beautifully curved panels, the front one having a bib spoiler at the bottom. This is coloured black to match the 'A' frame (see top image). The result is an aerodynamic drag improvement of nearly 20% compared to the Conqueror and Elite models, which were already far ahead of the competition.

The new caravans were taking shape but two major hurdles still had to be overcome - how to join everything together and how to eliminate wood from the floor.

For many years caravans have had floors made of a plywood outer sandwich and a Styrofoam core, reinforced with a wooden skeleton. Under SMART (launched in September 2013) Swift had already replaced the wooden skeleton with one made from polyurethane but the plywood remained.

No other manufacturer had successfully produced a floor without plywood but Swift was determined.  A new rigid honeycomb material made from plastic showed promise. Eventually Swift came up with a five layer sandwich that retained Styrofoam at the core but covered each side with the honeycomb material overlaid with a specially woven glass cloth. The components are bonded together in a laminating press to produce a floor with great rigidity and lightness. Swift took the new floor and subjected it to enormous bending and twisting forces until its limits were fully understood.

SMART HT floors contain no timber products and are bonded into a strong aluminium frame with thermal breaks to prevent any condensation. There is absolutely nothing to rot.

Now Swift had to join everything together to form a very strong box. For the floor, sides and roof Swift chose a specially designed aluminium framework into which the body panels could be bonded. There would be no screws or bolts. To prevent internal condensation, thermal breaks were incorporated, just as happens with aluminium double glazing. The awning rail is let into the framework so there is no external protrusion to cause drag when towing.

frame system
Special aluminium framing sections bond the sides to the floor and roof

This left question of how to attach the front and rear panels. There were two problems to be overcome. Firstly the aluminium framework could not easily be bent into the nice flowing curves required by the CFD software. Secondly, smoothing the panels had potentially reduced their rigidity.

As you might expect the solution was a high tech one. It involved producing special corner jointing pieces using a process known as Structural Reaction Injection Moulding, or SRIM for short. A two part resin is injected into a mould containing fibre reinforcement. It's used by car companies such as Lotus and Aston Martin to produce components that are very light but extremely strong.

This cutaway shows how the front awning rail bonds to the other components. The SRIM moulding is the dark section at the rear
corner detail

With the SRIM mouldings providing much strength, a much smaller and curve-able aluminium section was able to be used for the front and rear awning rail sweeps. This section locates the edges of the end and side panels.

A significant advantage of the SRIM jointing system is that the front bulkhead has been able to move forward to give more interior room. In some models this has been used to give longer front bunks or a larger washroom, in others the overall length of the van has been shortened.

Once the prototypes were completed they were subjected to many hours of testing on the tortuous track at Millbrook in Bedfordshire.  Then it was time for chief designer Chris Milburn to spend many weekends away, fine tuning the new caravans for maximum practicality and comfort.

srim The SRIM rear corner moulding is visible in this washroom cupboard

New methods of construction always raise concerns about repairability. In response Swift says that SMART HT has been designed with repairability in mind from the outset. The fact that all panels are GRP (except the rear, which is ABS) is a big help here as minor knocks and scrapes are easily dealt with. In the event of more serious damage it is possible to cut out and replace a whole body panel.

The introduction of SMART in September 2013 involved the commissioning of a £1.25M routing machine capable of machining whole sides, floors and roofs in one go, and to an accuracy of 0.25mm. Swift says the new machine epitomises what SMART and SMART HT are all about - and that is the  ability to produce finished components, both large and small, to a very high degree of accuracy.

The weight saved by SMART HT has allowed Swift to fit items such as this domestic towel radiator

The result is that they fit together exactly, first time, every time, thereby minimising the opportunity for operator error and enhancing the quality of the end product. Couple this with the use of modern materials to save weight and improve durability and it's easy to see why Swift is so enthusiastic about its new touring caravans.

Commenting on the finished product Nick Page, Swift Group Commercial Director said, ‘We have spent over five years carefully researching materials and construction methods to ensure the new SMART HT construction system provides the best engineered caravans Swift has ever made.’

The cost of SMART HT is such that, for the time being at least, it will be confined to the Elegance and Continental models.

March 2014