Tauranga divers are suggesting the wreck of the container ship Rena on Astrolabe Reef could become a top diving attraction.

Marine biologist, Tauranga based commercial diver and New Zealand Underwater Association board member Shane Wasik says retaining the whole or part of the 236m long wreck on the reef will be one way for the Rena to return something to the Bay.

Rena's position on the reef as mapped by Rosalind Spink, LOC.

'We thought this right from the very beginning,” says Shane, 'but everybody was really emotional about it at the beginning, and we had the oil spill which is really bad.

'It wasn't the right time to think about that, they needed to get the immediate environmental problems off it, but now we are kind of on the other side of it we can start thinking about what can be done to regenerate business.

'Looking forward it can be quite a good attraction for the Bay.”

The Rena, or a section of the ship, would become part of a wreck dive trail across the Bay of Plenty, which includes the steamship Taupo, near Karewa, the tug Taioma at Motiti, the trawler Seafire at Whale Island.

'It's not only diving, people like fishing on wrecks as well because they attract big fish.”

Salvage of the Rena is going to become uneconomic, says Shane.

The Rena was purchased by its present owner Costamare for $11.25 million.

'It just depends what the salvors do,” says Shane.

'The ship's worth however many million dollars and whatever the instructions to the salvors, are it comes to a point where the actual salvage cost outweighs the cost of the boat – almost like writing off a car when you crash it.”

The bow section is hard and fast on the reef and won't be able to be towed free, says Shane.

'It's not going to get craned off or anything like that, so it's difficult to find out how they are going to do that.

'Whether they are going to have people there to cut it up and take it away in sections.”

Ocean swells, winds and storms are going to take their toll over time.

'The longer you leave it the more structural failure it's going to get and the more chance of some of it actually sinking,” says Shane.

'I don't think the back of it is going to actually break off.

'I think what will probably happen is it is slowly going to settle down and then just settle down in the water and slip down that side of the reef.”

The Rena is sitting on top of a cave that was a popular dive site.

The water there immediately drops off to about 40 metres then goes down to about 60 metres.

Taking another wreck as an example, the wreck of the former troopship President Coolidge sunk in 1942, is one of the world's top 10 dive sites.

The sinking ship was beached on a reef and then slipped back down the reef wall.

The top sits in about 20 metres and the bottom is at about 70 metres, says Shane.

'It is on a big slope. That's quite typical of shipwrecks around the world. A lot of them sit in that position.

'If Rena does slip back off the reef that's what it will sit like.

'Obviously it depends what the gradient is.

'It is real steep there – it might slip further down which means the top section is in quite deep water.

'It might be 20-30 metres before you get even start getting onto the wreck, but that's still fine for divers.”

The wreck of the Taupo is in 34 metres, giving divers using air, a bottom time of about 20 minutes, says Shane.

'Wrecks are great attractions all round the world; Scapa Flow, Truk Lagoon, Bikini Atoll, Vanuatu.

'In New Zealand there's the Canterbury, the Tui up in Northland, the Seafire at Whakatane.

'There's even the Mikhail Lermontov in the Marlborough Sounds. These are all big attractions, so looking forwards a few years there are definitely positives.”

He's unsure of the legal situation. Where ships are scuttled to create dive attractions resource consent is required and the wreck must first be stripped, and tanks emptied.

'I'm not sure of the maritime laws behind a wreck and its abandonment, or if they can walk away from it,” says Shane.