I have to agree vith Gazesby, that you can't sail against the Wind.
The weather have changed since the viking age and the wind pattern should have been more east - west than today. It should have been more in favor for the sailing route those days.

When the vikings should sail, they waited until the weather condition were the best possible.
When the vikings should plan a sailing route they took the direct line from start to finish.

The Vikings did not crossail. As Gazesby said " this is dificult if not possible"

Instead they used a kind of system where they placed a stick on the mast to wide out the sail( hope I spell this right)

Using this system gave the vikings the ability to sail with the wind from a 45 degree angle from the front of the ship.

This way they almost sailed against the wind.

Reading some books about this these days hoping to find more information. Hope this gave you an answer

Tigger