The Transport Accident Investigation Commission said it could take some time to find out whether anything could have prevented the fatal accident on the Kaipara Bar.

Seven families are mourning their loved ones, who drowned when the boat they were in tipped on the bar on Saturday.

One man is still missing.

Chief Investigator Captain Tim Burfoot told Larry Williams there's a lot of information that's yet to be determined.

"The vessel, the people driving it, the people on board- what were really looking for is what can we take out of this. I mean its a tragic event, people lost their lives and we just hope that's not in vain, so were looking for anything that will help us stop it happening again" said Burfoot.

Captain Burfoot said it could take up to 18 months to ascertain the causes.

But he said they have the ability to make safety recommendations at any time if urgent safety issues are identified.