The ‘Spruce Goose' was the largest flying boat ever built, and has the largest wingspan and height of any aircraft in history. The brainchild of aviation and movie mogul Howard Hughes, the Hughes H-4 Hercules made its first and only flight in November 1947, a marvel of modern technology, but which would go down in history as a technological white elephant.

Sixty years later another wealthy Californian, Larry Ellison, finds himself owner of a 90-foot trimaran, the most hi-tech and technologically advanced sailing boat ever constructed. Like Hughes's ‘Spruce Goose', Ellison's super-boat is in danger of becoming another irrelevant and expensive white elephant. Ellison, whose fortune from his Oracle software empire once ranked him as the world's richest man, and which still places him well inside the world's top 20, commissioned the boat to be constructed for a match against Swiss billionaire Ernesto Bertarelli to contest the 33rd America's Cup.

Established in 1851, not only is the America's Cup considered the most prestigious racing event in the yachting calendar, it is the oldest ongoing sporting contest in the world, having been around longer than the modern Olympic Games, the Football World Cup or any other competition that springs to mind.

What also makes the America's Cup unique is that if you win it, you own it. The winner earns the right to run the competition to his rules and to his liking - within the terms of a hundred-year-old document called the Deed of Gift. In times of extreme disagreement, disgruntled tycoons can resort to the Deed of Gift, which gives the New York Supreme Court the authority to settle such disagreements. When Bertarelli's Swiss team Alinghi won the 2003 Cup in Auckland, he brought the Cup back to Europe for the first time since 1851 and hosted a very successful event in summer 2007 in Valencia. Bertarelli's team then announced that the next Cup would take place again in Valencia, in summer 2009, with a brand new Spanish yacht club, the CNEV, as the official challenger to Alinghi. Other potential challengers, and in particular BMW Oracle, believed the CNEV was merely a puppet challenger cooked up by Alinghi. The Americans accused the Spanish of having formed a marriage of convenience with Alinghi so as to secure Valencia as the host city once more, with all the many economic benefits that such a privilege brings. The rules were excessively skewed in Alinghi's favour.

Ellison's team BMW Oracle took Alinghi to court, and when Justice Cahn from the New York Supreme Court ruled in the Californian's favour, Bertarelli was forced to accept his rival's challenge to contest the Cup in huge multihulls - measuring 90ft by 90ft. In anticipation of winning the court case, BMW Oracle were already well advanced into the design and construction process of their new multihull while Alinghi were caught on the back foot. Alinghi's boat has yet to emerge from the yard in Switzerland while the American team already has many weeks of sailing under its belt.

The first few days of sailing on the new boat were like taking baby steps for the crew, even for sailors as accomplished as three-time America's Cup winner Russell Coutts or helmsman James Spithill. "The mast height is something none of us is used to," says Spithill, the team's young Australian talent. "When I looked up at it the first day we went sailing, I thought ‘God, we've got it wrong!' It's too big." Spithill has cut his teeth in America's Cup single-hulled keelboats which on a good day will chug along slightly faster than 10 knots through the water. Until recently these boats were seen as cutting edge, but they look monolithic compared with the scale and performance of the new BMW Oracle toy, which is capable of travelling at more than twice the speed of the wind.

Even after just a few days of getting to know the boat, building up the loads and understanding of the limits of this boat piece by piece, Spithill was already talking some impressive numbers. "We've been very conservative so far, but the top speed has been around 30 knots, in about 10 to 12 knots of wind." Such performance in the sail-powered world is almost unheard of, and just a few years ago would have been considered science fiction, but Spithill says there is a lot more to come. "We've not even come close to seeing the thing at full performance," he claims, and nor are they likely to for some time yet.

Because they are pushing new boundaries in the sport, they haven't yet explored the thin line between ultimate performance and catastrophic failure. Unlike the keel-bound monohulls which traditionally inhabit the America's Cup, these multihulls are easily capable of capsizing (tipping over sideways) or pitchpoling (tripping over themselves forwards). Spithill and his colleagues have capsized on regular occasions in their excursions on Extreme 40 catamarans, all part of their learning process to understand the workings of multihull sailing. But to tip over this 90-footer would probably result in the disintegration of the boat and a few broken limbs too.

The team takes no chances when training aboard the new boat, with everyone wearing crash helmets and PFDs (personal flotation devices). Quite apart from the risk of capsizing, there is the danger of hitting a submerged object, animate or inanimate. Before sailing the boat out of Anacortes for the first time, Spithill took a helicopter ride out over the area of the Washington State coast line to survey the area. "We counted at least 12 killer whales in the space of half an hour. There are also quite a few logs in the water, and initially we were quite worried about sailing the boat there. So we always had a powerboat riding about 100 metres in front of us, and they could radio back to us if anything was in our way. That would just about give us time to take avoiding action, hopefully!"

Fortunately the boat never struck anything during its first weeks in Anacortes, but as winter drew in, the team decamped to San Diego for some warmer weather training in more open water, where they could really open up the throttle on this extraordinary boat.

Back in New York, however, where the lawyers have been continuing to wage war in the New York Supreme Court, the latest appeal has gone in Alinghi's favour. Even though construction of the Swiss answer to Ellison's wonder boat is almost complete, Alinghi is now pursuing a new tack for the 33rd America's Cup. With the credit crunch and economic gloom and doom having set in, the Swiss defender, the reinstated Spanish challenger and nine other potential challenger teams have been busy working on a new design rule for a much smaller, far less ambitious single-hulled keelboat.

The aim for the new class is for it to be more in keeping with these austere times that we now find ourselves in. This wouldn't be the first time that the outlandish America's Cup has scaled back its ambitions to suit the changing economic climate. For many, the J-Class yachts of the early 20th century mark the golden age of the Cup, when the likes of Sir Thomas Sopwith and Sir Thomas Lipton did battle in 130-foot leviathans. But with the arrival of the Great Depression in the 1930s, so the America's Cup scaled down to much more affordable 65-footers called 12-Metre yachts.

Alinghi have lost interest in defending the Cup in big multihulls, although they have been training hard all summer in case the legal battle went against them. Earlier this year team skipper Brad Butterworth was licking his lips at the prospect of doing battle with the American team in giant trimarans and wondered if this was the dawn of a new era for the Cup. Asked whether he thought outlandish multihulls were the future of the America's Cup, the Kiwi commented: "I think it's up to the guys that own the teams to make that call, but if it was me I don't know why you'd go back. These boats are not cheap, this is an expensive regatta with just two teams in it and, when you've built one of these boats, I don't see why you'd bother going back to something that's going to be slower."

However, now that Alinghi is focused on forging a new and cheaper future for the Cup in slow keelboats, Butterworth and his cohorts no longer show any public interest in the multihull option. Which means that the 90-footer being constructed in Switzerland might never sail, let alone race. On the other side of the globe, however, Spithill and Co continues to train for a battle which may never happen. "All we can do from a sailing team's point of view is be ready to race. We've been amazed at this multihull world, it really is a different world to what we're used to, and it's been great fun learning about it. We believe we've got a solid case in the court room, but our job as sailors is to understand this boat and get it up to speed."

As things stand, the 33rd America's Cup will take place in yet-to-be-designed keelboats and so the 90-foot giant trimaran looks set to become an expensive (at least US $10m) irrelevance, a mere footnote in America's Cup history. Its one possible redemption could be a crack at the sailing speed record which was recently set by a French kiteboarder using equipment worth just a few thousand dollars. In October Sebastien Cattelan was first to break the magical 50 knot speed barrier with a run of 50.26 knots. Larry Ellison has never shown much interest in speed records, but if his 90-footer is to avoid the same ignominious fate as Howard Hughes' ‘Spruce Goose', it could yet earn its place in the sailing annals as the boat which surpassed Cattelan's record.