New Zealand's first plug-in electric boat had its first public encounter with Tauranga Harbour yesterday and passed with quiet, flying colours.

''I wanted to be the first person to do it - the stupidest one,'' Sean Kelly quipped after putting the working prototype through its paces around Sulphur Point.

Kelly, whose day job was running Pacific 7 work boats, said battery-powered boats had been tried overseas but not in the same way as his prototype.

He has spent more than $200,000 getting the project to the prototype stage and doubted he could recover $70,000 if he opted to sell the first craft out of his Electric Boats Ltd stable.

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''It is the research and development that costs a lot of money - New Zealand needs innovators,'' he said.

Kelly said the idea popped into his head three years ago, planning began a year later, and the last 12 months had been spent putting things together.

''Heaps of things tripped me up along the way,'' said the electronics technician and marine engineer.

His innovative design ideas included shaping the bow like an American Indian canoe, with the working design drawn up by naval architect Nick Herd. Another staff member Harrie Alma from Holland helped with the final stages to bring Kelly's dream to fruition.

Sean Kelly at the wheel of his all-electric boat, with Harrie Alma, the Dutchman who helped build it. Photo / John Cousins
Sean Kelly at the wheel of his all-electric boat, with Harrie Alma, the Dutchman who helped build it. Photo / John Cousins

''We are all mates, there is no hierarchy, no us and them,'' he said describing the teamwork that led to the unveiling.

Once Kelly got title to his piece of Sulphur Point's new marine precinct, he intended to launch himself into manufacturing battery-powered boats or converting conventionally powered boats.

He was realistic about the commercial prospects, saying that, like solar-powered houses, electric boats were not at the price point where it made perfect economic sense.

Kelly would initially target lake, river and aquaculture uses, with clients like DOC, regional councils, Niwa and the owners of fish and shellfish farms.

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It would be perfect for something like an oyster farm because, unlike a conventionally powered vessel, his boat left zero residue in the water, he said.

The boat has gained a lot of traction on social media, with a Facebook post last week attracting 23,000 page views.

Tauranga's trail-blazing electric boat with a bow shaped like the prow of an American Indian canoe. Photo / John Cousins
Tauranga's trail-blazing electric boat with a bow shaped like the prow of an American Indian canoe. Photo / John Cousins

''There has been a lot of interest from Australia.''

Although the upfront cost was currently about twice a conventional power package, all-electric boats and yachts made long-term economic sense, he said.

The weight of the Tesla smartcar batteries under the deck behind the wheelhouse did not count against his electric boat.

He ended up with a similar weight to an motor and fuel set-up because the two three-phase AC electric motors weighed less than half an equivalent internal combustion engine.

And the weight of the batteries added to the stability of the boat, rather than stability being upset as fuel was used up.

The engine can produce 147 hp - more than what was realistically needed, so there was less stress on components.

The battery would last about an hour at the top speed of 25 knots, or much longer at cruising speed.