It's a sight you'll see nowhere else: a race around a circuit that's half sandy beach, half blue sea, hard-fought with a putter and then a roar by more than 60 amphibious boats.
They are Sealegs, the product of Kiwi ingenuity, invented and manufactured in Auckland. Although they are exported to 55 countries around the world, their greatest concentration is on Waiheke Island, where they are used year-round to drive from bach to beach and then into the water for a spot of fishing.
On one day a year, though, the Sealegs camaraderie becomes serious competition when their owners take part in the Onetangi Beach Races. Being held next Sunday, 11 February — the date is dictated by the timing of low tide on Onetangi's two kilometres of wide, sandy beach — the Sealegs race is for many the highlight of the day's programme.
From a line scraped across the wet sand, the teams run to their boats, fire up the engines and trundle impatiently along the beach.
Then they head into the water, retract the wheels and transform instantly into racing craft, water pluming up behind them as they skim around the buoys and back to shore. Wheels down, engines up and they're back into trundle mode again as they vie to reach the finish-line first to claim the honours.
It's an event the originators of this annual, and free, family day out could never have foreseen back in the 1890s. Organised now by Waiheke Rotary Club as a fundraiser for local community groups and charities, the profits this year will purchase such diverse needs as dictionaries and defibrillators.
But for the thousands of locals and day-trippers who flock to Onetangi, it's all about the classic pleasures of a day at the beach, supplemented by the fun of the races and competitions.
While the Sealegs race is the greatest novelty on the programme, there are the classics too: horses send the sand flying as they power along the beach, and cute, hairy ponies in miniature racing sulkies are driven by children in slower-motion but equally fiercely-fought races.
Segways skim silently along, defying gravity; and lovingly-maintained old tractors do their best to give the impression of speed as they lumber down the beach, drivers bent over to lessen wind resistance.
There are running and wheelbarrow races for the kids, and some intense rivalry between the island's police, ambulance, coastguard and fire crews in their obstacle race.
Between races, spectators can go for a dip and fuel up afterwards at the food trucks and stalls or in one of Onetangi's restaurants; or they can divert themselves with the other entertainments.
There are sandcastle and sand sculpture competitions, a Big Dig for the kids, and the Fashion in the Field contest for women, men and children.
A Silent Auction for $14,000 worth of donated goods runs throughout the day and includes accommodation, restaurant meals, wine and even a fishing trip — just not, though, in a Sealegs.