UPDATE 1-Sailing-Ainslie aims to rule America's Cup new wave with historic 'Britannia'

(Adds quotes from Ainslie)

By Alexander Smith

PORTSMOUTH, England, Oct 4 (Reuters) - Ben Ainslie named his new multi-million-dollar America's Cup yacht "Britannia" on Friday as he launched the revolutionary foiling AC75 he hopes will bring international sport's oldest trophy back to Britain.

Ainslie's INEOS TEAM UK are aiming to challenge Emirates Team New Zealand for the America's Cup in Auckland in 2021 and the futuristic boat will soon be put through its paces on the waters of the Solent, near his base in Portsmouth, southern England.

INEOS TEAM UK is the fourth team after New York Yacht Club's American Magic, the defenders Emirates Team New Zealand and Prada's Luna Rossa to reveal their take on the design rules for the 36th America's Cup.

The 2021 event will be contested in monohulls which will spend most of their time with their crews "flying" above the water, with only their foils submerged.

"A huge amount of effort has gone into it from the team... We're really excited about getting out on the water and learning from this boat," Ainslie, Team Principal and Skipper of INEOS TEAM UK, told Reuters after the launch of "Britannia".

The design is the first iteration of the yacht that will travel to Auckland, with teams allowed to build two versions.

"Those learnings will go into our second race boat and into the America's Cup itself in 2021, so it's a really critical period in the campaign," Ainslie said, adding that the advent of 75-foot foiling monohulls would be "really something to watch".

With the financial backing of Jim Ratcliffe, the founder and chairman of British chemicals group INEOS, Ainslie is aiming to beat the other challengers for the cup to take on New Zealand.

"You can sail with pride under the name Britannia," Ratcliffe, who chose the name in homage to the famous cutter built in 1893 and raced by British royals, said before the torpedo-bowed black hull was lowered into the dock.

INEOS, which also sponsors the cycling team formerly known as Team Sky, is pouring more than 110 million pounds ($136 million) into the venture with Ainslie with the aim of recouping the "Auld Mug", which was first won in 1851 on the Solent by the schooner "America".

Despite numerous efforts during the intervening years, no British crew have managed to win the cup, although Ainslie has tasted victory in the event, lifting the trophy when sailing as tactician on Oracle Team USA in San Francisco in 2013.

Although the team have "a reasonable idea" of what to expect from its AC75, thanks to simulators which the design and sailing team use ashore, the dynamics are hard to predict and these were likely to present new challenges to the sailors, Ainslie said.

The first opportunity the British team will get to try their design against their rivals is in April 2020 in Sardinia, where the yachts will compete in the first of the America's Cup World Series races in the build-up to the 2021 event itself. ($1 = 0.8113 pounds) (Reporting by Alexander Smith; Editing by Toby Davis and Clare Fallon)