[JPLeRouzic]

From Scandinavian countries to Malta, you only have to cabotage, but that does not mean they used the same boat in one travel, most likely they progressed from outpost to outpost, where one generation settled in one outpost and the new generation searched for new adventures abroad.

For perspective, the Roman empire imported tin from Scotland (~3500 miles/~5600km).

On the contrary, going from Norway to Iceland, then from Iceland to Greenland, and then to Vinland in a few generations is a great maritime feat.