Carbon monoxide poisoning is one theory behind the deaths of two Launceston men aboard a boat moored in a Hobart marina.
But police won't discount other possible explanations, although they have all but ruled out suspicious circumstances.
The pair, aged 58 and 56, were found dead by the boat's owner on Prince of Wales Bay in Derwent Park, in Hobart's north, about 8.45am on Monday.
Detectives, forensic officers and marine safety experts spent much of Monday combing the 10-metre cruiser, dubbed the Double B, to determine what happened.
It was the second time in little more than 24 hours that emergency services visited the vessel.
In the early hours of Sunday morning, paramedics airlifted a seven-year-old girl and her father, the Double B's owner, from Wineglass Bay on Tasmania's east coast to the Royal Hobart Hospital when the little girl became ill because of an undisclosed medical condition.
The dead men stayed behind, moored at the Prince of Wales Bay marina on Sunday night and slept there.
When the boat's owner could not contact the pair at 7am on Monday, he went to the jetty at 8.40am and found their bodies.
"He's obviously traumatised - two of his good friends are deceased," Detective Inspector Rob Gunton told reporters.
Police said fumes from a generator on board may have caused the deaths but were hesitant to rule out any non-suspicious causes.
They have not said whether the girl's illness was related to the tragedy.
The dead men had been holidaying on the cruiser since December 28.
Police are now awaiting the results of post mortems on the two men.
