To make a sail is almost as big a job as building the boat. The material was wool or in a few cases hemp.
The sail making was no everyday textile production. Taking into account how much time and material was needed, a good number of people must have been involved over a long period of time.
For a sail of about 100 square metres, wool from about 225 long-haired sheep was needed. To prepare and spin the approximately 300,000 metres of yarn took 1,250 days, (almost 3 1/2 years for one person). And that is assuming a 12-hour working day. The work was probably shared between a number of people to reduce time.
After that, the loom would be warped. When the sail cloth had been woven, which probably would have taken about one year for one person, it would be fulled and sewn together and finally treated with fat, grease or some other water repellent material in order to be really waterproof.