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Police searched the Frankton Arm of the lake for the fifth day yesterday, after Matthew Duncan (46) set out from an area near the TSS Earnslaw slipway about 9.30am on Sunday on Sundance II.
The vessel travelled several hundred metres from the slipway and then stopped in the middle of the lake.
Mr Duncan has not been seen since.
The police national dive squad has been using sonar equipment to search the deep waters of the lake.
Senior Sergeant John Fookes said the team had completed searching an area about 400 metres square.
"We have not completed [searching] the area of high probability yet, so we will continue doing that today," Snr Sgt Fookes said yesterday.
Police have called on the navy to provide more advanced sonar equipment with the capacity to search larger areas.
"The equipment will ... increase the speed of the search," he said.