Some very good information in there! Here's a more or less direct answer to my question in the op:
According to Anna Nørgård, from the Viking Ship museum in Roskilde, a wool 61 square metre sail, woven in a twill with 8 threads in warp and 5 threads in weft, would take c. 4,148 hours to spin and weave. The preparation of the yarn, warping, and set-up would add another 830 hours. Altogether, it would take her c. 5,000 hours, or 416 days to make such a sail if she would work twelve hours a day (Nørgård 2016). However, if weaving in a tabby the spinning and weaving would only take c. 3,477 hours, excluding the 830 hours needed for preparation of the fibres, warping and set-up.
But this is only a small fraction of the textiles needed, because the 33 Vikings crewing the ship need clothes, and in the North Sea, quite a lot of them:
Apart from the clothes they wore, it is likely that each crewmember brought at least one extra set of clothes on a journey. Based on archaeological analyses of textiles in combination with experimental archaeology, it has been estimated that each crewmember had a minimum of clothes representing more than 6.5 kg of raw materials, or 30.5 square metres of fabric, which would have taken 3,343 hours to spin and weave (Table 2). Furthermore, well-made nautical clothing, possible of leather, and sleeping covers would have been necessary for survival. If all crewmembers would have brought the same amount of clothes and outfits, this equated to 215 kg of raw material, requiring more than 11,000 [sic] spinning and weaving hours (Table 3).
(There's a 0 missing in the last sentence of this paragraph, it should be 33*3343 ≈ 110,000 spinning and weaving hours; Table 3 has the correct number.)
The need for raw material was still substantial; c. 331 kg of raw material equates to wool from 331 sheep. According to modern calculations these sheep would need 33.1 hectares of well-fertilised pasture (10 sheep/hectare (Bender Jørgensen 2012; Fag undated). Even if the Viking Age sheep were half the size of modern sheep, and only used half the pasture, more than 16.5 hectares were needed (20 sheep/hectare).
This fits kinda nicely with one of the conclusions from Bret Devereaux's series on textiles, which led me to this question. With minimum comfort meaning one new full set of (Roman) clothes per year, Devereaux concludes (emphasis his):
Using the average of Aldrete and Fischer’s figures (erring a little high to account for Fischer’s lack of preparation time) we might figure something like 2,683 hours to produce our 220,000cm² minimum requirements. Our upper ‘comfort’ level might be three times this or 8,049 hours. [...] Put into working terms, the basic clothing of our six person farming family requires 7.35 labor hours per day, every day of the year. Our ‘comfort’ level requires 22.05 hours (obviously not done by one person). [...] A lone woman could, if she spun in almost every spare minute of her day, on her own keep a small family clothed in minimum comfort
Another way to put this, I guess, is that one woman working her hardest can keep herself and one other person comfortably clothed. Or, it takes half a year for one woman to comfortably clothe one person for a whole year. That makes a lot of sense, if you think about it: fibre and textile work is overwhelmingly done by women and overwhelmingly what women do in these societies, and women are half of all people.
With 7.35 hour working days it takes ≈ 680 working days to make the sail from before. So even at half a woman-year of labour per sailor, clothing the crew of 33 is substantially more work than making the sail. But actually these Vikings are bringing ≈ 450 woman-days of clothes each, so it's an even bigger difference. That's almost 2.5 times more than the comfortably clothed Roman; Devereaux's estimate is 66 m² for comfort for a Roman family of six, so 11 m² per person, less than the 30 m² per Viking in Andersson Strand by the same factor.
I mean, obviously the Vikings need to be dressed much more heavily travelling the North Sea than someone farming near the Mediterranean does. But with the estimates in the previous paragraph, if Mediterranean sailors dress roughly like people on land, clothing the crew dominates rigging the ship in terms of textile work.
This does make me wonder what minimum/comfortable standards of clothing looked like in Scandinavia compared to in the Mediterranean... in the colder climate it's going to take more to stay warm, it's as simple as that.
I think someone commented on Devereaux series on making iron that behind every Roman legionary there were a dozen woodcutters fuelling the furnaces and forges that make his sword. I guess the upshot of all this is that behind every Viking raider there are three women keeping him warm and dry.
(Hmm. I'd still want to know how much woodworking labour goes into the ship. Andersson Strand doesn't say anything about ropes for rigging either. But man, pre-industrial textile production SUCKS, the crew's clothes probably come out the vast majority anyway.)