At first glance the boat pictured here looks the stuff of fantasy - you would be forgiven for thinking that Darth Vader had retired from the dark side and taken up sailing. Last week, though, the 1065bhp Earthrace gunned its twin engines and set off on what its crew hopes will be a record-breaking blast around the world.

If all goes according to plan, it will slice 10 days off the powerboating record for circumnavigating the globe, which now stands at just short of 75 days. The crew of four will face some of the most treacherous waters in the world, with waves the size of houses, pirates and storms that could capsize the precariously balanced trimaran. And they must do it all at an average speed of 25mph while at sea. It is the equivalent of driving around the world at motorway pace.

“Things can become pretty brutal if you get stuck in a storm so we expect a hard-arse 24,000 miles ahead of us,” said the boat’s captain, Pete Bethune, via satellite phone as he sailed to the Azores from Spain last week. “Last year one of my crew suffered a cracked rib and a dislocated collarbone in heavy seas. You get lots of bumps and bruises when you’re going through big waves.”

That accident happened during a previous attempt at the record, which was abandoned after the craft collided with a fishing trawler. The nighttime collision, after three days of storms, left one Guatemalan shark fisherman dead and another injured, and Bethune was held for nine days in a military camp while officials investigated.

“We’ve definitely had a few adventures over the past couple of years,” he says. “The first day in the Guatemalan camp was a little intimidating because I didn’t know what to expect. They treated us well but when you’re not used to being greeted at port by 30 or 40 soldiers with machineguns, it’s pretty scary stuff.

“We’ve also been shot at by the Colombian navy, who thought we were drug runners. There’s still a bullet hole in the boat.”

The 78ft-long £1.5m speedboat has been a five-year labour of love for Bethune, a former oil worker from New Zealand. His vision was to build a vessel capable of smashing the world circumnavigation record of 74 days, 23 hours and 53 minutes – a feat achieved by the British boat Cable & Wireless Adventurer in 1998.

The attempt has become an obsession and Bethune has been threatened with bankruptcy on a number of occasions. Instead of admitting defeat, though, the married father of two mortgaged the family home, sold practically everything he owned, including his company, and then borrowed the rest of the money he needed from family and friends.

The result, after 18,000 hours of hard labour, is a powerboat that would have Roman Abramovich drooling. “People have said that I must be mad,” says a chirpy-sounding Bethune from the cockpit of his superboat. “I guess a little madness helps.”

Earthrace began its attempt on the world record - the pinnacle of powerboat challenges - at Sagunto, in Valencia, on the east coast of Spain, last Sunday. On board are four permanent crew: the skipper, Bethune; the navigator, Adam Carlson, 22, from Onsala, Sweden; the engineer and pilot, Mark Russell, 31, from Richmond, Surrey; and the cameraman, Rob Drewett, 31, from Kent. There is space for one additional crew member; for a fee of £10,000 a guest will be able to take part in a leg of the race.

On leaving the Mediterranean, the carbon-fibre vessel, built in Auckland, headed west and out into the Atlantic to the Azores. After that, the proposed race route takes in Puerto Rico, the Panama Canal, Mexico, San Diego, Hawaii, the Marshall Islands, Singapore, India, the Suez Canal and then back to Valencia (passing through the two canals is required by the race rules).

“Our chances of beating the record are about 50-50,” Bethune says.

“Already we’ve had problems with the autopilot and have had to drive manually. On most boats that’s okay but on this it’s like trying to contain a raging bull.”

Aside from the external dangers of navigating some of the most dangerous waterways in the world, the crew also face cramped and difficult conditions on board. Most worrying is the boat’s evacuation procedure should the Earthrace capsize. If that happened the vessel’s hatches would be underwater, leaving the crew with just one option: axing a hole in the side of the boat large enough to fit the life raft through. The axe hangs ominously on a cabin wall.

“Life on board depends on the weather. If it’s bad the crew gradually get worn down but if the boat’s going well and the weather’s fine then this is the best job in the world,” Bethune says.

“Luxuries are basic but we eat pretty well and we’ve all got our own iPods to enjoy. We all like a bit of meat so occasionally we have steak, and other than that we might have a chicken stir-fry or a tuna salad in the evenings and fruit and biscuits for lunch.”

The top speed of Earthrace is an impressive 40 knots, or 46mph. In order to beat the world record, Bethune aims to travel at 20-25 knots (2329mph) while the boat is in motion for 65 days.

The three-hulled boat’s design enables its chiselled prow to pierce straight through waves rather than skimming over them. The technique is controlled by up to 2½ tons of water pumped into a ballast tank in the bow, which adds weight to the vessel’s nose to minimise vertical movement.

As a result, the craft has the ability to charge through waves at great speed, in effect going underwater, rather than ride over them: the more water pumped into the bow and the faster Earthrace is travelling, the more the boat pierces the waves.

“In sea trials off Auckland we’ve already experienced 80-knot winds and 40ft waves. We had about five metres of water coming over the windshield, which was scary as hell. Theoretically, though, Earthrace can tolerate piercing through seven metres of sea.”

Despite the boat’s impressive top speed, beating the world record has been only one half of the target for Earthrace. Its captain has also set out to complete the trip in a sustainable way – an ambition he takes very seriously. His boat is fuelled by 100% renewable biodiesel; its modest emissions are counterbalanced with bought carbon offsets, so the voyage has, Bethune says, a “net zero carbon footprint”.

If his dream is borne out, he and his crew should be nearing the finishing line towards the end of June.

Between now and then, the team face an uncertain future away from their families. Bethune’s two daughters are aged 12 and 13. “One of the worst things is obviously being away from home for so long,” he says. “In the past two years I think I’ve only had three months at home.

“But if we end up crossing that finishing line, then we’ll have done what we set out to do and it will all be worth it.”