Dario's Lab

Paradox Foiling A Class Catamaran

The first Carbonix branded product, Paradox demonstrated the fledgling company’s ability to commercialise America’s Cup technology.

The vision was to create a competitive series-built product as a showcase to lend credibility. Credibility that would open the door to the aviation market that was the ultimate target for scaling.

The plan was to select a competitive technologically unrestricted international class and embark on a development cycle to achieve a generational improvement. This would be proven on the racecourse, and productionised at a competitive price point.

The A Class was rife for a shake-up, having type-formed around a simple high-efficiency displacement concept. Their rig’s characteristic high aspect-ratio was driven by the imperative to ‘unstick’ the windward hull (and achieve maximum righting moment) with minimum apparent wind. Masts were sensitively tuned to crew weight in order to automatically depower upon reaching maximum righting moment.

Having limited sail area and beam, the class incentivises efficiency. There is a high sensitivity to drag, even when it is a result of additional righting moment. For example, at various times the class experimented with small horizontal ‘winglets’ on the rudders to provide some pitch stability (prevent nosediving). But the small additional drag of these modest surfaces proved to be a nett loss on balance around the course. Similarly, high-volume hulls with plentiful reserve buoyancy, as used successfully in bigger more powerful multihulls, gave way in the A Class to fine, piercing, low-freeboard shapes. All in service of minimising drag.

The unique properties yielded by the Carbonix composites design and build process opened up a new design space.

Being able to make hydrofoils thinner, lighter, and stiffer than anything that had gone before meant we could achieve significant foil assistance, or even full foiling, with a much smaller low speed drag penalty than would be possible with incumbent materials.

This application aptly demonstrated the possibilities of the unique technology at the heart of Carbonix. We could design and build unprecedented foil shapes incorporating precise curves and bends without compromising structural integrity. The sections we could specify were considerably thinner than the contemporary state-of-the-art. And the structure’s dynamic behaviour was favourable.

The images above show some details that I remain very proud of. The complex curves in the main foils allowed lift to vary with ride height and dihedral to vary as the foil was lowered through the hull. The hull interfaces pioneered ‘sausage’ rotating bearings and dynamic rake (AoA) adjustment.

The rudders were revolutionary, incorporating an ‘L’ horizontal stabiliser/elevator. This greatly reduced drag compared to a ‘T’ by optimising the pressure distribution around the bend (junction drag) and minimising the number of free (vortex shedding) tips. Ls also maximised horizontal span under the rule. Making the elbow at the bottom work structurally was a significant challenge and definitely would not have been possible with conventional manufacturing techniques.

Above left is the initial tooling set that would be used to make moulds of the version 1 foils. Committing to having this radical hydrofoil tooling machined was a leap into the unknown – or the future.

It represented the beginning of a long development cycle, with many lessons learned, paving the way for the acceptance of foiling as a net gain around the racetrack. An adventure that led to the ongoing work still progressing at Carbonix (though now applied to air rather than water).

Though the initial design was carefully simulated and engineered, the first iteration shapes just plain didn’t work in the real world. Specifically, the foil section was prone to ventilation and the lift-to-drag ratio was just too unfavourable.

But three or four iterations in, the concept started to show promise. As well as refinements to the section and manufacturing details, the shapes became perhaps more radical, as demonstrated by the tooling pictured above right. Model, build, test, rethink, repeat!

The rudder cassettes embodied beautiful engineering. Departing from the then common kick-up style, they gave easy adjustability of span (depth) and precise control of rake (AoA of the horizontal). They had to be strong enough to react the significant loads, yet minimise friction for steering and retraction. All whilst being repeatable (and interchangeable) in production, at a realistic cost.

Paradox pioneered the lateral gudgeon pin solution for dynamic balance (compensation). The vertical rotation axis put some rudder area ahead of the pivot point to lighten helm feel. But as ride height increased, this compensation area decreased (thanks to the raked leading edge) to give a more ‘positive’ helm feel at high speeds.

For the eventual production version, the cassette system moved into the hull, allowing ‘sealing’ between rudder and hull, which significantly cleaned up the wake.

Above is the final production prototype. The most notable visual difference being lower freeboard hulls, taking advantage of foil lift to maintain clearance between the trampoline deck and the wave tops.

Though the bows had a fine piercing peaked deck, the underwater sections forward were very ‘U’ shaped. Volume was pushed down, out, and forward to maximise the prismatic coefficient and encourage planing to assist take-off.

This design represents growing confidence in the ability to remain foilborne for the majority of a race. Downstream of this confidence are subtle departures from the norm, like keeping the hulls vertical (rather than canted out) and moving the mast forward in the boat.

The ‘secret sauce’… The images above show production underway at the facility on Cockatoo Island. The precise prepreg laminates, taking shape in carbon tools in a clean room environment, call to mind aerospace more than marine practices.

The hull shells used a Kevlar honeycomb sandwich, with minimal bulkheads bonded using glue fillets rather than secondary tapes. Beams were moulded in one piece using bladders, and incorporated landings to be bonded to the hulls.

Despite unprecedented stiffness and the addition of complex hydrofoil controls, Paradox platforms routinely came in under the class minimum weight.

Above and below you can see some images of production underway. A big part of successful engineering is selecting the right material for each application. The main carbon structure interfaced with billet aluminium fittings, bronze hard points and Teflon bearing surfaces.

Having started to rack up good results on the racecourse, soon Paradox platforms began hitching rides in 40’ containers to exotic locations all over the world. For instance, the grey boat pictured above-left in front of the Cockatoo Island workshop moved to somewhere snowy in North America (a disproportionate number of boats was ordered in grey, presumably because that was the colour of the prototype that featured in magazines, web reviews, and regatta reports)…

….And others popped up on Lake Garda, in Auckland, and off Dubai.

As well as selling complete platforms, Carbonix commercialised foil retrofit kits that were in great demand. These consisted of the main foils and rudders, together with cassettes, trunkings, bearings, and adjustment systems, complete with installation instructions.

Perhaps fittingly, Carbonix products were identified by Team New Zealand sailors as being highly relevant to their experimentation when learning to make America’s Cup catamarans fly. Thus began a collaboration that saw me spend considerable time at their Auckland base, once again contributing to America’s Cup development! This culminated in top placings at the Worlds – another treasured achievement and fond memory.

Following the Worlds, with the Carbonix order book swelling, the class administrators decided to change certain rule interpretations with the pretext of levelling the playing field. In retrospect, this was the beginning of what I’d characterise as regulatory overreach that robbed the class of stability.

Paradox was tweaked to comply and remained highly competitive. But the rule climate gave rise to a surge in demand for ‘turbo’ foils – designed to maximise flying stability regardless of newly invented restrictions. In response we quickly developed a kit that could be retrofitted to class-legal boats without permanent changes (so the boat could still be raced by swapping out the turbo foils for now tortured class-legal ones).

We supported the two product lines (boats compliant with ever-tightening arbitrary restrictions and retrofit ‘max fun’ foil kits) for a few more seasons until the aeronautical work grew to the point of demanding all our attention. I look back on this period with great satisfaction, knowing we proved what we’d set out to with abundant clarity.