Urgent safety recommendations were issued by the commission yesterday, as an inquiry continued into the capsize and sinking of the 11m Easy Rider in Foveaux Strait on March 15.
The bodies of John Karetai (58), Peter Pekamu-Bloxham (53), Shane Topi (29), and Boe Pikia-Gillies (28) were recovered.
The bodies of the vessel's skipper Rewai Karetai (47), 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 Easy Rider had stability limitations, but it could not yet confirm whether that factored into the boat's capsize.
As a precaution, the owners and operators of boats known to be made to the same design were being contacted and asked to respect such limits.
But the commission's chief investigator, Captain Tim Burfoot, said the design for boats like Easy Rider might have been used in various shipyards throughout New Zealand and it was not known how many vessels in operation were built to similar limitations.
Easy Rider was believed to be built about 1975 to a design dubbed Owenga, as one of at least nine.
Maritime New Zealand found three similar boats being commercially operated in New Zealand and another thought to be in Tonga.
The authority would not disclose whether any of the boats were operating in Otago, although one was based at Bluff.
Capt Burfoot said Easy Rider was loaded with a fair amount of equipment at the time of its sinking.
Some was stacked as high as the roof of the vessel's wheelhouse.
"The commission has evidence that since the Owenga class fishing vessels were built, authorities have recognised that they had limited reserve stability and could become unstable if too much weight was loaded on deck," a commission release stated.
It planned to publish its final Easy Rider investigation report by March 2013.
Former Easy Rider owner Matenga Taiaroa, a first cousin of missing skipper Rewai Karetai, previously said the vessel was a "brilliant sea boat".
Mr Taiaroa, who was muttonbirding and therefore not available for comment yesterday, was initially shocked to hear of Easy Rider's capsize.
The Otakou resident, a retired fisherman of about 40 years, wondered how Easy Rider had capsized and whether it was overloaded.
"Normally, it wouldn't have even looked like capsizing," he said days after the incident.
Mr Taiaroa's brother, the late Te Iwi Taiaroa, had also owned Easy Rider.
