You see them moored in the lagoon, the yachts: each one conveying their cargo of multimillionaire art collectors to the prosecco-sodden art ritual that is the opening of the Venice Biennale. This June, it was Roman Abramovich's that dominated: to this unmarine eye, at least, it seemed as vast and unassailable as a Royal Navy frigate.  At this year's Frieze art fair in LoRegent's Park, London, which opens to the public on Thursday, one artist has taken the sometimes queasy-making connection between extreme wealth and the artworld to its logical conclusion: by attempting to sell a 65-metre superyacht at the fair.  Buy it as a boat (it will be built to order by CRN of Ancona, to the buyer's specifications), and it costs €65m (£60m). Buy it as an artwork, authenticated by the German artist Christian Jankowski, and it will cost €75m. If that seems a little steep, a smaller, 10m Aquariva Cento motorboat is on display at the fair, among the Robert Rymans and Tacita Deans. That one's €500,000 as a mere boat; €625,000 when officially designated art.  According to Jankowski, the boats are not artworks until he has handed out a certificate to the new owner, who will then have the right to call the vessel "Christian" (for the motorboat) or "Jankowski" (for the superyacht). There is nothing, he admits, to stop the owners calling the boats what they like even without paying the extra. But without the certificate, he said, "it won't be sculpture".  The idea is, he said, a play on the yacht-culture of wealthy art aficionados: "When you see the yachts lined up at Venice it is an exhibition in itself." But he also admires the formal qualities of yachts. "The yacht is the perfect sculpture, a perfect self-contained vessel of information."  His idea is, he said, an extension of the idea of the readymade artwork – like Marcel Duchamp's urinal, but bigger and more seaworthy. And the owner will be a participant in their own piece of performance art, he said: "I'm interested to see whether some collector has the capacity to push what they do to an extra level."  Jankowski's project is one of Frieze art fair's special artist's commissions, with a title, The Finest Art on Water, borrowed from yacht marketing literature; but Luca Boldrini, the specialist salesman on hand at the fair, more used to boat shows than art fairs, is deadly serious. "If we can sell this as art it will enter a different stratosphere, and I am pretty confident we can," he said. "American artist Donald Judd was putting chunks of cement in the desert and people were able to appreciate it is art."  In the wider world of the fair – which hosts 173 stands of contemporary art from galleries from London to Sao Paulo and Beijing – the talk was of how the art market was faring against the backdrop of a eurozone teetering on the brink and domestic unemployment at its highest since 1994. "It feels like a parallel universe," said one Frieze art fair veteran in mild disbelief, as she surveyed the cavalcades of the polished European super-rich who were stalking the fair on its VIP-only opening day.  Despite the collectors being out in force, "the fair feels quite subdued", said Georgina Adam, the art market editor-at-large for the Art Newspaper. "Dealers are nervous, even if they don't admit it. You can see that most have played safe with what they have brought; there's very little challenging work."  By the afternoon of the VIP opening day – by which time, in more buoyant years, whole stands' worth of art might have been snapped up – dealers were reporting "tons of inquiries" but steady, rather than speedy, sales.  At Victoria Miro, gallerist Glenn Scott Wright said there were strong sales of work by Japanese artist Yayoi Kusama, an exhibition of whose work has just opened at the Pompidou Centre in Paris. One gallerist, who asked not to be named, said: "Before, it was like a supermarket dash. Now, it's much more considered – and that can be good. With Greece imploding and Italy wondering what's what, of course it's going to make a difference. People are even walking more slowly this year."  At Thomas Dane Gallery, artist Michael Landy – famous for once having destroyed all his possessions, as a work of art – was offering a free drawing in return for your credit card, which he would destroy in an impossibly elaborate shredding contraption, a Heath-Robinson-like device covered in scissors, swords and skulls. It felt like a sign of the times.
In Regent's Park, playthings of the megarich become sculpture, while talk is of how the art market is faring in the economic storm