A solo boatie in his 70s whose empty cruiser washed ashore probably went overboard and is highly unlikely to have survived, police say.
The 10-metre fibreglass vessel was discovered at Kingston Beach, south of Hobart, around 2pm on Wednesday, sparking a large-scale air, water and shore search.
Police say the man, who lived on the boat, likely went into the water. They believe he wasn't wearing a life jacket.
"(We're) very concerned," Tasmania Police commander Jason Elmer said on Thursday afternoon.
"If the man has entered the water, given the current water temperature and the overnight temperatures, that makes survivability ... very low."
The air temperature in Hobart dropped to 6C on Wednesday night, while the average spring water temperature is around 12C.
Cmdr Elmer said the man was heading down the River Derwent after leaving Prince of Wales Bay in Hobart's north.
"We're not sure what has occurred. We're not exactly sure what his intentions were for the day," he said.
Conditions on Wednesday morning were reasonable with light wind.
Police didn't initially know who owned the boat but on Thursday morning confirmed it belonged to the man, whose name has not been made public.
The search area was expanded on Thursday afternoon, with police expected to review efforts and continue examining the vessel for any clues.
