A Viking Ship is on its way to the British Isles from Norway.
The Sea Stallion, the biggest replica Viking vessel ever constructed, is bound for Kirkwall in Orkney.
It is part of a 1,000-mile journey from Denmark to Ireland over seven weeks; and aims to understand better the seamanship of early Norsemen.
A BBC team is following the "living archaeology" project in a support boat to make a film for the Timewatch series later in the year.
The volunteer crew has already faced severe weather conditions on the journey from Denmark to Norway, with several individuals being taken off the Sea Stallion temporarily because they were showing the early signs of hypothermia.
"This journey has been tough so far but the crew are in high spirits and looking forward to reaching Scotland and sailing in the Atlantic," said crew member Louise Henriksen.
The weather could yet thwart the attempt to cross the North Sea by sail - the harsh weather conditions that have swept across the UK are predicted to bring a gale which could blow the Sea Stallion back towards Norway.
If that happens, the project's organisers may call for the ship to be towed by its support vessel. Skipper Carsten Hvid said: "The aim of the project is to test this ship out in the waters the original Viking ship sailed in.
"It's better that we get to Scotland and start sailing there, than spend the whole summer waiting in Norway for the right winds."
The original Sea Stallion was made in 1042, and 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 from about 300 oak trees and using 7,000 iron nails and rivets.
At 30m (100ft) in length, the Sea Stallion is said to be the world's largest reconstructed Viking vessel.
The ship hopes to reach Dublin in mid-August.
The ship's crew are writing a weekly diary for the BBC News website. More regular updates and a map of the ship's latest position can be found at BBC History's Viking Voyage website.
THE SEA STALLION FROM GLENDALOUGH
1. The crew of 65 men and women will sleep on the open deck, as the Vikings did, and take turn keeping watch
2. Satellite navigation equipment will make sure the ship stays on course. Vikings had to rely on the position of the sun and stars, the colour and movement of the sea and wind direction
3. Oak planks were cut radially for maximum strength, overlapped and nailed together. Axes and other tools used to make the planks were replicas of those used by the Vikings
4. The sail, mast, rigging and rudder on the original were missing so these have been copied from other finds
5. Shields, vital in battle, were tied over the oarports when the ship was in port
Sources: Viking Ship Museum, Denmark; National Maritime Museum, UK. Photos: Werner Karrasch and Erwan Crouan