Senior Sergeant Martin Paget, officer in charge of Police Maritime Unit, said the boat should be recovered by tonight.
"We have located the boat from the incident and we are undertaking activity at the moment to recover that so we can see what the cause was."
He said passing boaties saw a line in the water yesterday and reported the rope to a police boat in the area. Five police dive squad members were brought to Auckland first thing this morning, and had been out this afternoon, he said.
He said police were now searching from where the group began and ended their swim, from about halfway across from Martins Bay to Motuketekete Island.
"[The boat recovery] has allowed us to more narrowly define where to look for the missing person. And as a consequence tomorrow we are going to bring in some specialist equipment from the Royal New Zealand Navy to assist."
He said the Navy equipment looked "a bit like an unmanned submarine" and would allow police to search a wider patch of sea for a longer time.
"The Navy have some equipment that they use for searching underwater for searching for just about anything and we've successfully used it in the past to look for people underwater."
Mr Paget said the police boat and the divers would continue tomorrow and police would review whether to continue at the end of the day.
"We haven't got him back yet so that's the important thing for the family."
He said the investigation into what happened at sea was continuing.
"In any investigation into any accident we look at all potential causal effects. Clearly in this day and age alcohol may or may not be a factor. And we'll just look into whether or not that was a factor in this case. At this stage we only have reason to believe the missing person had anything to drink."
-APNZ
