The crew hope to learn more about Viking expeditions

The 30m (98.5ft) long replica, called Sea Stallion, is said to be the world's largest reconstructed Viking vessel.

It is based on a ship made nearly 1,000 years ago in Ireland, which in 1962 was excavated from the Roskilde fjord.

A crew of 65 volunteers will travel the 1,900km (1,200 miles) to Dublin, using only oar and sail power.

"The Vikings are coming back. Be prepared," Captain Carsten Hvid shouted before jumping onboard the ship.

The original, which was made in 1042, is believed to have taken part in clashes between the Anglo-Saxons and Normans in 1050-1060, when many Danish Vikings lived in Ireland.

The boat sank in the Roskilde fjord at the end of the 11th century, while defending the country's coast from Norwegian Vikings.

The replica was constructed with around 300 oak trees and 7,000 iron nails and rivets.

Rough weather

It has a top speed 15-20 knots, but is equipped with GPS satellite navigation and radar. A modern support boat with medical and rescue experts will also accompany the ship.

Return of the Viking warship

The aim of the voyage is to sail uninterrupted to Dublin across the North Sea and around the north tip of Scotland.

The crew say the toughest challenge will be the weather, with no shelter on the open vessel from crashing waves, wind or rain.

"After all, we are testing the construction. Can it resist the rough weather? And the nights get really cold," Louise Henriksen, a 27-year-old historian and crew member, said.

"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."