By Alexander Smith

PORTSMOUTH, England (Reuters) - Jimmy Spithill bounds from one side of his America’s Cup catamaran to the other in a couple of strides, deftly dodging the edge of the huge “wing” which drives this state-of-the-art sailing craft.

Oracle Team USA’s boat, which lifts out of the water on hydrofoils even in the light breeze, is a far cry from the more stately schooner “America” which first laid claim to the cup known as the “Auld Mug” in the same channel off southern England 165 years ago and after which sport's oldest trophy is named.

Since losing in 1851, British yachts have failed in every attempt to win back the America’s Cup, a statistic Spithill hopes will not change next year in Bermuda when he defends the trophy he won in 2013.

During a practice race ahead of the latest America’s Cup World Series event, a build-up to the 35th America's Cup itself, Spithill’s four fellow crew members are constantly on the move, bouncing off the trampoline that joins their two hulls.

They also skip through a web of ropes and controls as they harness the power of the aircraft-like wing and coax the 45 foot boat out of the water and on to its foils.

Despite a relatively light wind and calm seas, the hum of the tension in the rig and the foils slicing through the water makes for an eerie sensation, combined with an extraordinary acceleration which can see the boat reach speeds of up to 50 knots.

Skipper Spithill, who said at the launch of this weekend's event in Portsmouth that he wanted to make amends for a disappointing fifth out of six last month in Chicago, gives little away on board, but constantly watches his rivals as they jockey for position at the start of Thursday's unofficial racing.

He keeps a particular eye on home favorite Ben Ainslie, the British former Olympic sailor who has set up his own team Land Rover BAR in an effort to bring the cup home and who won in Portsmouth a year ago.

NOTABLE COMEBACK

Spithill and Ainslie sailed together on the U.S. boat in San Francisco during the last cup in 2013, winning against the odds in one of the most notable comebacks in sport as they recovered from 1-8 down to beat Emirates Team New Zealand 9-8.

Unlike Ainslie and other crews who have lost some of their members to preparations for next month's Olympics, Spithill and his sailing team manager Tom Slingsby are sailing in Portsmouth with their usual line-up.

The crew of Team USA talk to each other throughout the informal practice race, with a rare silence falling as they put all their efforts into "hiking" their body weight over the edge of the hull when the boat lifts off and "flies".

Although it is only a practice, they are clearly not pleased when Ainslie crosses the line ahead of them, quickly going over the points in the race they could have improved.

After Chicago, Spithill and the team not only scrutinized footage and data of their own performance, they also looked closely at everyone else's to see if there are techniques they can learn from.

Going into the weekend's real racing, Oracle Team USA and Land Rover BAR are on equal points in the overall standings, 10 behind leaders Emirates Team New Zealand, whose Peter Burling and Blair Tuke are preparing to represent their country in Rio in the 49er class.

Team New Zealand skipper and sailing director Glenn Ashby told Reuters ahead of the practice that this represents a chance for the team to try out new combinations and positions on the boat, something it will be doing in Portsmouth.

"It's a wonderful opportunity for us to run through some different guys, we've got a great depth of talent through the rest of our sailing team," Ashby said.

(Editing by Ed Osmond)