The Scandanavians were not wedded to clinker hull design nor was carvel a Basque trade secret.

Of course not. The important thing is that frame- built construction was strong and rigid enough to take the strain of sailing closer to the wind, and in worse conditions, than shell- built boats could manage. This in turn allowed the use of multiple masts and more complex and powerful sail plans. The function of the frame in the ship is more important than the planking- you can have overlapping planking with or without a frame, and with or without plank- to - plank stitching. Edge to edge planking needs a frame however. Also, the use of a frame doesn't necessarily imply design for Atlantic voyaging.

And the final development of the seagoing, framed, carvel built hull with more than one mast does seem to have occurred over a period of a hundred or a hundred and fifty years, along the Basque costline and neighbouring areas, and England was near enough to take part in that development. These ships enabled the Portuguese expansion along the African coast and eventually into the Indian Ocean. It also enabled the Basque, Breton and English fishing and whaling voyages that (probably) discovered the Grand Banks, and Columbus's voyages to "India" and more importantly the subsequent exploitation of the discoveries by Spanish adventurers.

Does anyone know enough Portuguese etymology to say which way their word for 'oak' (carvalho) developed - was the tree named from the ship or the ship from the tree?

But the important thing is that up to those developments no one had the technology to make much impact on the far side of the Atlantic, so much so that pseudohistorians desperate to populate preColumbian America with anyone except American Indians have to resort to forgery and tourist trinkets to push their claims.