Clockwise from far left: in 2000 the new Young America team were determined to max out the stiffness and aero-efficiency of their rigs. Introducing a small degree of twist with a very exaggerated section was shrewd – sadly it was not the rig the team should have been concerned with. Young America broke following a compression failure of the unidirectional carbon deck ‘planks’; Team New Zealand celebrate winning the right to challenge Alinghi in Valencia 2007 with their truss boom assembly clearly on show; Team NZ’s triangular boom used in 2003. Also of interest here is the plastic water screen by the rescue pack – clearly an issue had already been identified and the ‘hula-boat’ almost sank in race 1… before later losing its mast (opposite) and finally the Cup. Kiwi Cupworld is a happier place today
reliable honeycomb structure requires an additional weight-adding layer of film adhe- sive to ensure proper bonds between skins and core. Where the pre-preg resin in the carbon-carbon layer comes from both layers, honeycomb, with no resin pre- impregnated in it, needs the film adhesive addition. The honeycomb relies on this extra resin to create the tiny fillet structural connections with its cells. One solution is to cut lightening holes in
the sides, but that immediately becomes impractical because the open edges the cuts produce in the honeycomb/carbon structure need to be sealed, which is labour intensive and adds back weight. Instead, booms were made with sides and bottom faces removed and replaced with truss struts to support the unidirectional carbon-reinforced top channels, yielding moderate weight savings. Cup designers all had their own versions.
become known as the Millennium Rig? After 2000 mast dimensions and rotation
rules were tightened, the former effectively ruled out mandrel-moulded masts. At the same time autoclave curing was stymied when sparmakers other than Hall and Off- shore inexplicably dragged their feet in acquiring autoclaves (affording autoclaves could not have been an issue), relying instead on rather makeshift bolt-together clam-shaped ovens that barely held half the pressure of our ’claves. But rulemakers were sympathetic and the autoclave advantage was eliminated by a rule change for 2003, limiting oven pressure to three atmospheres, less than half the autoclave’s cure pressure. At Hall we felt the irony: for Luna Rossa
and Alinghi we had to have special Amer- ica’s Cup mast cure cycles at three atmos- pheres while our J/Boat and other inexpen- sive production boat masts were routinely cured at double the pressure. By 2007 the limits on pressure were still not fully lifted. During the early 2000s long flipper
plates were added to the top spreaders, first used just to smooth out contact with tightly trimmed genoas. As genoa roaches increased the flipper systems became more sophisticated with adjustment to not only
increase twist, thus opening the slot, but also allowing twist while still sheeting the genoas hard. For 2003 Scott Ferguson was hired by
Luna Rossa. While there, he and Luna Rossa technicians created another IACC milestone: they determined that if two smaller side shrouds replaced the single larger one, windage would be reduced. On Luna Rossa’s rig the forward shroud was a little bigger than the aft shroud, creating an effective teardrop shape that further reduced windage. Although rules forbade taping them together, the two rods were close enough to each other that the aft shroud was well inside the wake of the forward shroud. Ferguson remarked that, though it worked, pre-tuning the two shrouds for equal stretch was quite chal- lenging and very time consuming! For 2007 boom design evolved further
with the introduction of truss beam con- struction. A thin-walled honeycomb sand- wich monocoque is clearly a very light way to make a large-shaped boom. But these stiff, strong boom structures, though light, can be even lighter. First, the structural area of these booms is large with wide tops and bottoms and deep-depth sides. Second,
A typical boom was one of Alinghi’s that was effectively triangular in shape with a wide honeycomb structure on the top (com- pression) side. The ‘apex’ of the triangle on the bottom (tension side) was a strong carbon tube. The sides consisted of a sophisticated truss system. Where earliest honeycomb booms weighed about 100kg the best truss booms were weighing under 40kg by the end of the 2007 Cup cycle. Between 1992 and 2007 the America’s
Cup Class was hugely successful with just under 100 boats produced and almost double that number of rigs built. Participa- tion was in unprecedented numbers and competition was close and exciting. A credit to rulemakers and spar designers,
mast reliability was impressive. Except for collisions, and the aforementioned mast failures soon after launch of the first boats in 1992, only two masts failed during racing between 1992 and 2007. Compare that to the 12 Metre era when two masts once broke racing on the same day and a third broke earlier the same year. Ironically, the IACC era ended in a
similar fashion to the 12 Metre era: the result of Defender mis-steps that led to a rogue Deed of Gift challenge in 2010, only the second in Cup history. As a result an entirely new America’s Cup class ensued, with super-fast
powered by sophisticated wing sails. SEAHORSE 49
foil-borne catamarans q
BOB GRIESER/OUTSIDE
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