Wasn't one of Iceland main enterprises exporting fish to Britain/Germany?But it might be to haul it to Iceland and Greenland.
I'm thinking we'd probably need to push the timescale back a bit from the typical period of 1000 AD when Vinland was discovered because the knarr while fulfilling the minimal requirements for the trip to Vinland, probably wasn't sufficient for a safe/profitable trip.It would not be profitable to haul fish from the Grand Banks to Europe in a knarr.
I'm thinking of a scenario during the reign of King Haakon IV of Norway. Norway had just ended its civil war period, and Haakon was very much trying to increase Norwegian influence in all direction. OTL he gained control of Greenland in 1261, and Iceland in 1262. What if however Greenland had a much harsher 12th century, to such a point that it was all but dying out by start of Haakon's reign. Greenland could have maybe offered to recognize his authority decades earlier in return for aid and new settlers enough to revive the colony. As Greenland would be useless without settlements, Haakon could agree. He'd likely find it easy to wrangle together several hundred people and sending them off to Greenland, especially since the wars against Ribbung and Skule likely left more than a few people Haakon wouldn't mind exiling without officially exiling them. The cog had also become prominent in the 12th century, and Haakon was known for his large and powerful fleet. So there'd be at least a few cogs among the people sent. The cog might have been slightly slower than knarrs, but was (I think) a safer seagoing vessel and was capable of carrying almost ten times the cargo capacity.
These newer, fresher, and more adventurous settlers would be in a better place to expand to utilize resources outside of Greenland. I don't think it a coincidence that most of the exploration of the Vinland region was done in the decades after Greenland was settled. While they used Labrador for timber, it seems likely that as Greenland settled down they lacked the resources to have ships explore for a full year much less start entire settlements several weeks of sailing away. A second wave of colonization would be better positioned to expand further and tentatively settle a number of areas of interest. This second wave would also have a degree of royal backing. Haakon entered an alliance with Castille, so he was rather open to opportunities far from Norway itself. If some of his people came back from Vinland and told him of the empty (in this thread) Newfoundland, I don't at all think he wouldn't at least consider sending an extra few hundred people to settle it in hopes of it eventually sprouting into a second Iceland (which he spent decades working to annex). And even sending three or four warships from his fleet of roughly 300 with 50-100 soldiers would almost certainly be able to protect a settlement in New Brunswick, where the walnuts and grapes were, from any native attacks.
I think this scenario would be far more likely to succeed than the original Vinland discovery in 1000 AD. Cogs would render it a safer trip and make trading far easier, this effort would have a degree of royal backing from a king more willing than most to devote resources to peripheral areas far from home, and Norway to the best of my knowledge had relatively easy succession after this so a degree of support from Norway would potentially follow for decades. True, this Vinland would only have a bit more than a century before the Little Ice Age really kicked into gear around 1350, but that would always be a problem for an isolated colony that almost certainly could be largely cut off from European support. However if the Norwegian fleet was devoted early to maintaining trade with such a distant place, it could potentially develop better navigational methods and ship architecture that would allow contact with Vinland to continue in the Little Ice Age. Not to mention royal backing and support would make it far easier for Norse settlements on New Brunswick and Nova Scotia to grow and prosper, a place more likely to survive the Little Ice Age relatively intact than Newfoundland.
A 'successful' Vinland colony does not have to be founded soon after discovery in 1000 AD. It could be established anytime between 1000-1492 AD. Hell, it doesn't have to even be before Columbus. Denmark-Norway could have potentially settled it afterwards. Maybe Columbus' discovery reach a few people in Scandinavia who renew interest in Vinland. They could be tempted by gold after the Spanish conquests of the Aztec's. Or Denmark-Norway could have tried to establish Vinland after the breakup of the Kalmar Union as a power play for prestige. If Denmark-Norway could establish themselves in the St. Lawrence Bay/Newfoundland in the first half of the 16th century, they could potentially preempt/edge out French, Spanish, and Portugese interest in the Grand Banks. It wasn't till 1583 that the area was officially claimed by England, and it was only in 1630 that St. Johns gained permanent residents. While there's little chance Denmark-Norway could compete with England or France in the colonial game overall, or that Denmark-Norway could hold the region from them, arguably Denmark-Norway had near a full century after Columbus that they might have been able to opportunistically snatch up the St. Lawrence Bay region. That would be more than enough to establish a modest colonial Empire, especially compared to OTL, while still fulfilling a Vinland colony.