It wasn't being made to sign a waiver before I hopped on board Team New Zealand's new AC72 that made me nervous - apparently the team's legal department are kept busy enough as it is.

Nor was it being handed a helmet and an oxygen bottle to strap around my waist in case the super-sized racing machine should capsize and I get trapped under water.

It was hearing skipper Dean Barker briefing on the on-board comms before the start of the day's testing that he hoped to push the boat upwards of 40 knots - around 75km/h - on just its third day on the water and second proper sailing day.

Looking at the faces of the design team on the chase boat, they too were a bit uneasy about the skipper's plans.

But with the big event in San Francisco on the horizon, the sense of urgency in the Team New Zealand camp has been ratcheted up several notches since the launch of their second boat, New Zealand Aotearoa.

So as I gingerly climb aboard NZL05, I knew this was going to be no pleasure cruise around the Hauraki Gulf.

Moving around the boat takes some getting used to. As I stagger about on the netting like a new-born foal, clambering from one side to the other whenever a tack is performed, the crew sprint past me, easily traversing the distance between the two hulls in a couple of bounds.

I'm seated in the driest spot on the boat, right in the centre, but that does not save me from the odd dousing.

It is the windward crew that are most in the firing line, though, with Richard Meachem, the team's bowman, hunkering down to avoid the massive shower of spray as the windward foil kisses the water.

Today is considered a calm day, with a flat sea and moderate winds, but full wet-weather gear is a must.

The real ride begins when they head downwind.

During the testing of their first boat late last year, I watched in awe from a chase boat as the giant catamaran with the same dimensions as a tennis court (well, 3m wider, to be exact) flew above the water. It is quite another thing to be on board experiencing lift-off for the first time.

Sitting at the stern of the boat, it is an amazing sensation looking down and seeing both hulls flying clear, the turquoise water of the gulf swishing 5m to 6m below.

The expectation is when the boat loses its lift, it will violently crash back down into the water. But this proves not to be the case - instead, it smoothly glides to the surface like a mythical sea creature.

According to the on-board data, we get up to around 38 knots at one stage during a run - quite pedestrian by the standards of the new multihull class - and it doesn't feel as though NZL05 is even close to being pressed.

Boat one reportedly reached speeds of 48 knots, and there is the sense of untapped speed potential in the revised model.

After every couple of runs, the designers convene in the middle of the boat and hunch over their tablets, looking at the data for any areas where they can boost performance. With the new class, the designers are pushing the boundaries of foil and hull technology to places it has never been pushed before and they are in constant communication with the crew about the boat's handling.

The break also gives the exhausted crew a chance to take a breather.

The physical and athletic demands of sailing the boat have increased exponentially. Grinders don't just have to be big and strong, they also need to be quick and agile.

Rob Waddell believes the boat is about as big as it could be and still be sailed by people power - if it were any bigger it would need an engine rather than grinders alone.

Lurking menacingly, rivals are also closely monitoring Team New Zealand's progress, with the black chase boat of Oracle keeping watch on their training session trying to glean any nuggets of information they can send back to their bosses in San Francisco.

Their presence doesn't seem to bother the team - they are used to having their movements closely scrutinised. Even manoeuvring the catamaran out of the Viaduct attracts a big crowd, with those milling about the area and perched on nearby boats stopping to snap shots on their phones of the hi-tech racing machine heading out for a day of training.

"Go Team New Zealand, this is your year," one fan calls as the boat edges its way out through the small gap in the sea wall. Barker waves in acknowledgment, then fixes his attention back on the task at hand, acutely aware that the sum of those little things they discover in the testing phase may well be the difference in San Francisco.