The Navy vessel Manawanui is heading to the area to assist the recovery operation after searchers pinpointed where the plane ditched into the sea near Gannet Island.
Sonar images have mapped where the Beechcraft Baron is upside down, 56m below the surface, and the bodies of Mr Hertz, 58, and Mrs Hertz, 64, are believed to be trapped inside.
Their families today publicly thanked "the tremendous outpouring of support and condolences being offered to help us deal with the shock of our sudden and tragic loss".
"Knowing that they both touched so many lives in a positive way is a profound reminder of how much they meant to us in our own lives," the family said in a statement.
"We are comforted and proud to know they were not just beloved in our families, but also integral and engaged members of the community they loved in New Zealand."
The family said they were being supported by "energy and love" in Auckland, Seattle and "around the world".
"As we gradually awaken from our shock we are beginning to think about how best to recognise and celebrate the lives Eric and Kathy led and will share those plans at the appropriate time.
"We thank you all for your continued support and condolences in what is an incredibly difficult and sad time for us all."
Salvage company New Zealand Dive and Salvage said the retrieval of the couple would have to happen very quickly so divers' lives were not put in danger.
The company told Radio New Zealand any recovery operation would have to involve experienced divers who would need to act fast so they did not run out of air or suffer nitrogen narcosis, which could affect their brains.
Sergeant Warren Shaw of the Waikato police search and rescue squad described the find as a success, but said it was a small step in the overall recovery operation.
"Once we were able to identify the item of interest it meant we could narrow our search field considerably and deploy even more specialised equipment to the crash site."
He said the search team included police, Navy and Civil Aviation Authority (CAA) personnel.
The challenges faced by the agencies involved were difficult but not insurmountable, he said.
"We have the right people and equipment on hand, both in Raglan and elsewhere, available to deploy, and each agency remains committed to returning the missing couple back to their family."
CAA spokesman Mike Richards said an aviation expert was helping to identify parts of the aircraft found on the sea floor.
"With the aircraft being upside down, fully submerged and bedded in the ocean floor, it's quite a difficult task to make sense of the visual images that are being relayed to the team on the surface."
Mr Richards said police and Navy were working on recovery options to retrieve the occupants.
"Once this is done, the CAA can start considering ways to carry out the investigation as to establishing possible cause or causes of the accident.
"The co-ordinated efforts of the agencies involved are both substantial and remarkable."
