The bodies of a 58-year-old Newnham man and a 56-year-old Mowbray man were discovered on board a recreational vessel moored at the Gepp Parade Marina in the Prince of Wales Bay, north of Hobart, about 8.45am.

The scene was uncovered by a Hobart man who owned the boat.

Glenorchy detectives swarmed the marina for much of the morning and confidently ruled out foul play on Monday afternoon.

Glenorchy Criminal Investigation Branch Detective Inspector Rob Gunton said what killed the men would not be known until an autopsy was conducted – the results of which are expected to be given to police on Tuesday.

Suffocation from generator fumes was a possible cause, Inspector Gunton said.

It is believed the men – who were friends – were asleep on board ‘‘the Double B’’ when they died.

‘‘There’s nothing to indicate self harm or any other suspicious circumstances at all,’’ Inspector Gunton said.

‘‘There are numerous factors that are being investigated, which may have caused the death. We have some indications of what that may be, but ... until such time as we receive the results of the post-mortem examination, I’m not in a position to succinctly tell you exactly what the cause of death was.’’

Inspector Gunton said the pair were holidaying in Hobart with the boat owner and his seven-year-old daughter.

The owner and his daughter were not on board the vessel at the time of death, however, because the girl required urgent medical treatment about 12.30pm on Sunday while the group was in Wineglass Bay, on the state’s East Coast.

She was instead taken to hospital, while the 56-year-old and the 58-year-old Launceston men sailed back to Hobart about 10pm.

It was unknown if the girl’s medical episode was linked to the men’s deaths, but she made a full recovery, Inspector Gunton said.

The men had been holidaying in the Bicheno area with the father and daughter since December 28.

Inspector Gunton said the boat owner had been ‘‘traumatised’’ by the ordeal and said the dead men were his ‘‘good mates’’.

The boat owner initially tried to call the pair on their mobiles about 7am on Monday. When they did not answer, he travelled to the marina where he made the grim discovery.

The boat will be examined by police as part of the investigation and detectives plan to speak to ‘‘numerous other people’’ about the incident.

The families of both men have been notified.