After three years of planning, a decommissioned fishing trawler took just 10 minutes to sink

A 60-year-old decommissioned fishing trawler has been intentionally sunk off the coast of Hawke's Bay to create an artificial reef and dive site.

The project's been driven by LegaSea, a not for profit organisation dedicated to restoring the abundance, biodiversity and health of New Zealand's marine environment.

Sinking the vessel has taken three years of planning by LegaSea, and it took just 10 minutes for the Twofold Bay to disappear underwater to the cheers and toots from a flotilla of about 40 boats. She's now lying in about 17 metres of water near Napier, off the edge of Pania Reef.

Brett Rigby from LegaSea Hawke's Bay and the Twofold Bay Trust told RNZ they had followed the world's foremost guidelines, the London Protocol. It required two years of consultation and resource consents, followed by a year of volunteers working on stripping the boat back.

"It's been 800-plus man hours... you have to strip it of everything harmful to the environment - the biggest job was taking out the engines, removing all the oils and making it dive safe," he said.

And because of that, they carefully sunk the vessel by opening up holes in her side to let gravity, and a fair bit of concrete, do the rest.

"We don't want a big explosion and it to blow to pieces, we want to keep the whole boat intact so it's a really cool dive experience for people," said Rigby.

Chris Scott from LegaSea said divers were excited to explore the wreck.

"As the ship breaks down... that will create habitat for more marine ecosystems and biodiversity regeneration.

"The whole goal of this is to create more structure in the Bay, which is typically quite an open and exposed area, where people can dive safely and catch some kai," he said.

Over time the ship would form an artificial reef that would become home to a number of marine organisms such as sponges, green lipped mussels, barnacles, anenomes, and sea squirts - all of which attract other fish species such as blue cod, snapper and king fish.

Ngati Kahungunu marine scientist Shade Smith said it's ironic that all of that would be created by an old fishing trawler.

"It's got a reputation as a bit of a demon at fishing, so it's sort of come full circle in its life now which is a little poetic.

"We need to transition away from bottom trawling and super charge restoration efforts, and this is a great example of a coming together of a lot of sectors," he said.

Smith was intrigued to see how the vessel developed into a reef, and would be monitoring it regularly.

"It's relatively close to Pania Reef which means there will be some connectivity between ecosystems there and the ship," he said.

Seafood New Zealand chief executive Lisa Futschek was also there to witness the scuttling, and is pleased with the collaboration between commercial and recreational fishers.

"It's got multiple benefits and as a shared user of the moana, it's fantastic. The project has been a long time in the making - it's really exciting," she said.

The location's been approved by Mana Ahuriri Trust, who are the mana whenua of the area and hold marine customary title for the site.

Trust member Joe Reti is looking forward to experiencing the new reef after an 18 month rahui is lifted.

"We can get back in there and start taking our rangatahi, as well as myself, and diving the reef like we used to dive Pania in the past," said Reti.

Something the president of the New Zealand Sport Fishing Council, Scott Macindoe, said would be worth the wait.

"Restored abundance in sorting out the marine envionement is a hugely long game.

"For me it's about community having belief in themselves and each other. Together we are limited only by our imaginations," said Macindoe.