New Zealand have been analysing patterns in Ben Ainslie's racing, honing their technique and making subtle final adjustments to the sails and foils of their AC75 boat as the America's Cup holders prepare for the British challenge.

But according to the NZ team's CEO Grant Dalton, much could depend after three years of exhaustive preparation on the "trigger pull" -- the last 25 seconds when the boats line up to cross the start line -- when the sailing heavyweights meet head-to-head to contest the Cup for the first time on Saturday.

"Their starting was good and I think we're going to have to be careful in the start box," Dalton said of Britain's showing against Italy in the battle to challenge for the "Auld Mug", adding that while the British sailors may be battle-hardened from the experience, they are likely to be tired.

Dalton said he expects the speed of the two high-tech AC75s, which rise above the water on hydrofoils, to be "pretty equal", meaning whichever team gets off the start quickest has a greater chance of controlling the rest of the race.

And because "the fastest boat always wins the America's Cup", if one has a "slight edge" it is likely to win, Dalton said on Wednesday outside New Zealand's Barcelona base.

"Although the cliche is that it's going to be close, it may not be, because we will find out quite early on if one boat has an advantage," said the 67-year-old, who still gets nervous in the final days before a first-to-seven America's Cup "match".

Dalton said he has "massive respect" for the approach Ainslie and his billionaire backer Jim Ratcliffe have taken in the British campaign and in working as the "challenger of record" on the future of the America's Cup.

But he is wary of the British skipper on the water.

"Ben's an enigma in some ways because he's such a really lovely guy ... But on the water, he's not nice at all," he said.

"If he throws something random, that can be good and bad because ... he might catch himself out because he's not practised that," Dalton said of Ainslie, 47, who is the most successful Olympic sailor.

For New Zealand skipper Peter Burling, who has two America's Cup wins to his name as well as three Olympic medals, the hours of reviewing the British decisions and their handling of specific situations are about to be put to the test.

"It's something we'll have to wait and see how it plays out," said Burling, 33, who has been working with his crew to stay sharp as the challenger series has unfolded without them.

"The America's Cup is a race to win the last race, not necessarily the first. You've got to continue to improve and evolve and I think our challenger ... has been doing a good job of that so far ... But we're really happy with the progress we've been making as well," Burling said.