A 30-metre replica of a Viking longship glided out of Denmark's Roskilde fjord Sunday, with 65 crew members determined to sail the ship across the North Sea and around Scotlandto Ireland.

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The Sea Stallion of Glendalough sails with a flotilla of modern vessels Sunday from the fjord in Roskilde, Denmark. ((John McConnico/Associated Press))

Irish Environment Minister Dick Roche was among the roughly 4,000 people watching the Sea Stallion of Glendalough begin the attempt to relive the perilous journey its Viking forebear made 1,000 years ago.

The ship is billed as the world's biggest and most ambitious Viking ship construction.

It was modelled after a warship excavated in 1962 from the Roskilde fjord after being buried in the seabed for nearly 950 years.

"The Vikings are coming back. Be prepared," skipper Carsten Hvid shouted before jumping on board the wooden longship.

"You will be very welcome in Dublin on this occasion," Roche replied.

The crew of sailing enthusiasts and history buffs plans to sail the ship on a 1,900-kilometre voyage to Dublin, which was founded by Vikings in the ninth century. The planned arrival date is Aug. 15.

The expedition aims to gain a better understanding of the challenges the Vikings faced on their long journeys. There is no shelter from crashing waves, wind and rain on the open vessel. The crew have a minimum of privacy in the confined space.

Crew members wearing baseball hats, windbreaker jackets and life vests hugged family members before boarding the ship.

"I am not nervous but there is some funny tickling in my stomach," said crew member Lasse Rahn, a 21-year-old student from Flensburg, Germany. "I am so excited."

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A crew member waves as the Sea Stallion of Glendalough sails Sunday. ((John McConnico/Associated Press))

Unlike the Vikings, the crew is aided by modern technology: a GPS satellite navigation system and radar and the ship will be accompanied by a modern support vessel with medical and rescue experts.

The goal is to sail non-stop to Dublin by crossing the North Sea and rounding the northern tip of Scotland. But the plan could change depending on the weather.

'We all are a bit crazy'

"If we get 10 hours of rain and storms, we still need to be able to laugh to survive," said Claus Oreskov, 46, a Danish crew member.

"What all crew members have in common is that we all are a bit crazy."

Using replicas of Viking-era tools,craftsmen built the 6.8-tonne Sea Stallion using 150 cubic metres of oak and 7,000 hand-forged iron rivets.

The Vikings entered recorded European history in the late eighth century, when Christian monks chronicled the first Norse raids on the coasts of northern Europe. The Vikings were also skilled craftsmen and traders, establishing commercial networks as far away as Constantinople — today's Istanbul.

In Britain and Ireland, the raids gradually grew into full-fledged invasions led by Danish and Norwegian kings. The first Viking settlements in Ireland have been dated back to 840.