Oracle Team USA will need to rely on adjustments to their style of sailing rather than anything design related if they're to be able to pull back Team New Zealand's 3-0 America's Cup series lead, says Team NZ designer Dan Bernasconi.

Both teams are currently amid a rest window, a period Jimmy Spithill has deemed "the most important five days of the campaign", where they've promised to leave no stone unturned in their search for potential improvements to their boat.

Bernasconi confirmed they had noticed some recent alterations on the American boat, specifically their method of trimming the wing and how they're setting up their foils.

While conceding there are certain tweaks they'll be able to make to their hardware, the former McLaren F1 team member believes the restraints in time mean the most critical changes should come from the sailors themselves.

"Anything in terms of fundamentally changing the boat is pretty limited in five days," Bernasconi told Newshub.

"There definitely are things they can change, and obviously if we were 4-0 down we'd be looking at what we could do.

"The thing that's easiest to change is the way that you sail the boat."

That's precisely where he thinks the most significant development has come in the Kiwi camp since the earlier round-robin defeats to Oracle - the sailors are simply now more familiar and comfortable with sailing the boat itself.

"We've been making changes to the boat progressively…. but I think also, and probably more so, it's the sailors getting more confident in sailing the boat.

"We've been developing the boat pretty much non-stop since we launched, so the sailors have never had a stable platform to learn how to sail. They’ve been learning how to get the most out of the boat while we've been continually changing it under their feet.

"I think just getting lots of practice racing against other teams, particularly Artemis and BAR, has enabled them to push the boat a lot harder and find the limits and get the most out of her."

Not that the off-shore crew are resting on their laurels just yet, with the team unified in its commitment to capitalising on their impressive start now that the match's final stretch looming.

"We're not going to ease up now. We've been pushing really hard for over three years or so.

"We're still pulling out all the stops to make sure the boat is as ready and as fast as it can be next week."

Newshub.