This is the upright viking loom. This is how the viking sails were made. The sails were all made from wool or flax -- possibly hemp -- and took quite some effort.
One reconstruction sail had and area of 90 m
2 and used wool from at least 200 sheep. The weavers produced 157 continuous meters
of material 65 cm wide, weighing 90 kg. It took 7850 hours to produce, about 4.5 years for one person. Additional time was needed to stitch the pieces together.
The sail was eventually greased to make it wind and water resistant.