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A Wellington man has taken the New Zealand tradition of guys mucking around in their backyard sheds to new extremes by building what is possibly the country's first home-made two-man submarine.

In what could be the underwater version of The World's Fastest Indian, Brent Shaw's DryDive is one of the major attractions at this year's Hutchwilco New Zealand Boat Show at the ASB Showgrounds in Auckland.

After building a "couple of cars and hot rods", Mr Shaw sought out a new challenge six years ago.

"So I thought, hell yeah, a submarine would be great and I wouldn't get wet looking at the fish," he said.

Undeterred by his total lack of engineering experience - most of his mates saying he was "completely mad" and time off his 8000-hour project while he had chemotherapy for colon cancer - Mr Shaw set about his new task.

He learned welding, gas cutting and steel fabrication at a local polytechnic and spent two years on the design and planning as local engineers got on board with his idea.

"At the start they all thought I was mad, too, but as it took shape they were tremendous and gave me a lot of help and parts I needed."

After nearly 90 test dives in Lake Taupo and around Great Barrier Island over the past couple of years, he was ready to go public.

It's not for the claustrophobic, but DryDive can accommodate two adults.

The 2.1-tonne submarine, which is built of cor-ten plate steel and is powered by twin 80lb thrust electric motors and a 10hp diesel engine, has an automatic cabin pressurisation system and a closed-circuit television monitor attached to its snorkel.

DryDive can go to depths of 35 metres but can cruise "comfortably" at 10 metres for 100 minutes. The cost: between $35,000 and $40,000.

Mr Shaw said: "It's easy to transport and easy to launch. The hardest thing is towing it because petrol is so bloody dear.

"I think this is for anyone who wants to join the era of underwater adventure."

He is now looking at developing DryDive II, which will be built to Maritime Safety Authority standards.