A radial sonar is being used to comb the bottom of Lake Wakatipu as the search for a missing Bluff man enters its fourth day.
Matthew (Matt) Charles Duncan (46), set out from an area near the TSS Earnslaw slipway about 9.30am on Sunday on Sundance II, travelled several hundred metres and then stopped.
It then either drifted or made its way towards the shore and the Bay View Rd boat ramp, at Kelvin Heights about an hour later, however, late Sunday afternoon the boat was found to be empty.
Mr Duncan, the owner of Painting Solutions, has not been seen since.
The Police National Dive Squad arrived in Queenstown on Tuesday morning to assist in the search.
This morning Senior Sergeant John Fookes, of Queenstown, said the search teams spent yesterday in the search area - a ''box several hundred metres on each side'' - using a radial sonar to ''identify points of interest''.
"They've covered a good proportion but not all of the search area, or initial search area, and have not found anything of significance at this point,'' Snr Sgt Fookes said.
"So, the intention is that they will continue with that process this morning and throughout the day until such time as they identify a point of interest, or complete the whole area and then we'll reassess what method we use after that.''
Snr Sgt Fookes said the water depth averaged between 30m and 33m in the search area, which only allowed divers a small amount of ''bottom time''.
"It's far more practical to do a sonar scan and identify points of interest than attempt to search it using divers.''
He said police were grateful to the public for offers of assistance, in particular Real Journeys which had provided a boat ''the whole time''.
