Their six-metre vessel overturned in Great Oyster Bay near Swansea about 4.30pm and an EPIRB signal was detected by the Australian Maritime Search and Rescue Coordination Centre in Canberra.

The Tasmania Police Westpac rescue helicopter, a coast guard unit and local fishing boats joined the search for the vessel, which was located 90 minutes after it capsized.

The three men, all from Hobart's Eastern Shore, were treated for mild hypothermia by members of the Tasmania Ambulance Service at Little Swanport.

A police spokesman said it was believed the boat had been swamped by waves after a fishing line became entangled around the propeller.

All three men were wearing Australian standard life-jackets.

The spokesman said the men had broadcast a mayday message on their VHF radio before the boat sank and had also activated their EPIRB.

Tasmania Police Sergeant Charles Stingel said the signal - from a new digital EPIRB - identified the position of the vessel, along with a description of the boat and the name of its owner, which made "rescue coordination far easier".

Last February, 121.5MHz EPIRBs were made obsolete with the introduction of the 406MHz satellite frequency.

"Thankfully, the people involved in this incident were not injured," Sergeant Stingel said.

"I would also like to acknowledge the assistance provided by the boating community in general, who never fail to drop everything and assist in these situations."