The book Atlantic is where I came across it. Sand shoals force ships into the currents of the North Atlantic Gyre which the Portuguese mastered before tackling

The book Atlantic is where I came across it. Sand shoals force ships into the currents of the North Atlantic Gyre which the Portuguese mastered before tackling the Cape Bojador problem; see Volta do Mar [1] which has a great diagram. The problem was solved with math. [1] https://en.wikipedia.org/wiki/Volta_do_mar https://en.wikipedia.org/wiki/Volta_do_mar