“My understanding is that Portuguese cod fishing taught them the lessons of long-distance ocean travel”
That would most likely be the Basques rather than the Portuguese. The Basques encountered the Vikings in the 9th century and began building boats like them. And that may not have been the only thing that Basques learned from the Vikings. The Basques were supplying Europe with cod for years and wouldn’t reveal their source, but it surely had to be the Grand Banks off of then ‘undiscovered’ North America.
There’s two books by Mark Kurlansky that should be good sources on this, ‘Cod: the fish that changed the world’ and ‘The Basque History of the World’
Thanks for your post, and I’ll look into the Kurlansky book. Certainly the Vikings and, subsequently, the Basques pioneered north Atlantic fishing and exploration, but the 15th century Portuguese advance with the caravel design opened up the age of exploration.
Here for an interesting article on cod fishing history: http://pubs.aina.ucalgary.ca/arctic/Arctic37-4-520.pdf