The Transport Accident Investigation Commission has issued an urgent safety recommendation emerging from its inquiry into the capsize and sinking of the fishing boat Easy Rider off Stewart Island.
Eight people died and one person survived the tragedy on March 15.
"There appear to have been stability limitations with the Easy Rider which will be shared by other boats of the same design," said the Commission's chief investigator of accidents Captain Tim Burfoot.
"The boats can be operated safely within these limitations, but owners and skippers need to know of them first to do so.
"While these limitations have been known previously, it may be that information has not been passed on over the years with changes of owners, skippers and surveyors for these boats. The commission has asked the director of Maritime New Zealand to ensure that other boats of the same design are located and their owners are advised of this, and he's undertaken to take the necessary action."
The 11-metre vessel Easy Rider sank in Foveaux Strait at the start of a muttonbirding trip.
The bodies of John "Dukes" Karetai, 58, Peter "Peter-Boy" Pekamu-Bloxham, 53, Shane Topi, 29, and Boe Pikia-Gillies, 28, were recovered.
The bodies of the vessel's skipper, Rewai Karetai, and David George Fowler, 50, Odin Karetai, 6, and his father Paul Jason Fowler-Karetai, 40, are still missing.
Dallas Reedy, 44, was the sole survivor. He spent 18 hours in the water, clinging to an emptied petrol container before being rescued.
The Commission said at least five boats of the same design, built almost 40 years ago, may still be in service.
In the past authorities have recognised these boats could become unstable if too much weight was loaded on deck and in one case the surveyor recommended a plaque be placed in the wheelhouse warning skippers not to load too much weight on deck.
"The Commission has made preliminary calculations that support this view," Captain Burfoot said.
Maritime New Zealand spokeswoman Sophie Hazelhurst said most of the owners of similar boats had already been contacted.
"We're well underway with that work, so it's not going to be too difficult at all from that perspective. We know who they are and where they are."
Captain Burfoot said urgent safety recommendations were a mechanism to ensure matters which appeared to need attention could be addressed when they were found, rather than waiting for an interim or final report.
"I have to stress that the commission has not yet made a finding as to whether the issue highlighted today contributed to the Easy Rider accident, but it is of concern. Accidents and their impacts typically result from a range of factors coming together."
The Commission hopes to publish a final report into the tragedy by next March.