Matthew (Matt) Charles Duncan (46) has not been seen since Sunday morning, when he set out from an area near the TSS Earnslaw slipway, at Kelvin Heights, about 9.30am on the boat Sundance II.
The boat then either drifted or made its way towards the Bay View Rd boat ramp, at Kelvin Heights, about an hour later. However, late on Sunday afternoon, it was found to be empty.
Aerial, land and water searches since have failed to locate Mr Duncan, the owner of Painting Solutions.
The police national dive squad had been using a radial sonar to comb the lake bed through water made murky from silt washed in by heavy rain.
Senior Sergeant John Fookes, of Queenstown, said the search was focused on a "box several hundred metres on each side".
The depth of the water, between 30m and 33m, allowed divers only a little "bottom time", so the sonar was being used to identify points of interest that divers would then investigate.
"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 yesterday morning.
"The intention is that they will continue with that process ... 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."
