Bored with the luxury yacht? Personal submarines are a growing trend for the mega-rich.
So you've got the limo, the super-car, the luxury yacht, a penthouse suite and a country spread, and even the private jet. What's next on the toy list if you're one of the upwardly mobile one-percenters of this world?
How about your very own mini-submarine?
Recreational subs could soon be jostling for space on board the world's luxury yachts, if latest design trends are any indication. The first family-friendly five-seater has hit the market and could soon be vying to become the new must-have toy of the mega-rich.
The C-Explorer 5 was created by Dutch submarine maker U-Boat Worx to accommodate four passengers and a pilot, and has been dubbed "the world's first the subsea limousine".
This airconditioned mini-sub – which will set you back between $2 million and $3 million – can descend to a depth of 300 metres, reach speeds of three knots underwater and stay below the surface for eight hours.
A range of larger recreational submarines that seat many more passengers are also on the market, but because of their size and price - in the tens of millions of dollars - they are mostly pitched at the luxury resort market.
New developments in lithium-ion battery technology helped in the design of the C-Explorer 5, according to Erik Hasselman, sales and marketing manager at U-Boat Worx.
"It allows us to make a more compact, lighter and more manoeuvrable sub that can stay under for much longer," he says. "Recharging has also become much simpler with this technology, and charging the submarine could be compared to charging your iPhone."
He says that while the five-seater was created in response to demand from the tourist market, the yacht industry has shown the most interest so far.
The larger size does have its drawbacks, though. Only those with a 100-plus metre yacht – or a smaller vessel that is purpose-built for carrying a sub – will be able to squeeze the C-Explorer 5 on board, says Hasselman.
The market for recreational mini-subs is relatively new, according to Barry Jenkins, chairman of Superyacht Australia, which represents businesses that sell products and services to the superyacht industry.
He says he spotted a mini-sub – a single-seater – for the first time at an international boat show about five years ago, then a double-seater appeared, and now the first five-seaters are arriving.
"We're hoping to track down one of the smaller ones for the Sanctuary Cove International Boat Show this year," he says.
Microsoft co-founder Paul Allen and Russian billionaire Roman Abramovich – owner of the world's largest private luxury yacht, Eclipse – are among those who have their own mini-sub.
Other ocean explorer types, such as British billionaire adventurer Sir Richard Branson and film director James Cameron, have custom-built subs.
In March, Cameron descended 11 kilometres into one of the ocean's deepest nooks, the Mariana Trench, in his Australian-designed solo sub, Deepsea Challenger.
Another mini-sub maker, Triton Submarines, says it is working on the prototype of an 11,000-metre "full ocean depth" mini-sub model.
Developments in this area are being driven by acrylic manufacturing process improvements and advances in material sciences and electronics, according to Marc Deppe, Triton's vice-president of sales and marketing.
While U-Boat Worx has yet to make a sale in Australia, Deppe says Triton has sold mini-subs to Australian clients.
"Sadly I cannot name any of our clients as they tend to be very private individuals who require confidentiality in all of their dealings with Triton," he says.