So if these legends and tall tales were known to seamen, that means earlier Columbuses could have existed, right? We could presuppose any navigator who found a willing sponsor could have gone west. Hence the potential for more timelines.
Between this and the Toscanelli map, Columbus’ idea of sailing west goes from being a bit of a crapshoot it’s easy to assume it as at first to actually being kind of a brilliant idea and it’s 100% understandable why he decided to risk it.
I’m surprised no one thought to try it before him now.
Well just knowing someone went there and back again once or twice is not sufficient; it matters how risky and harrowing their voyage was, how low the chances are of surviving the round trip.
Navigational technology was advancing fast in the late medieval to early modern transitional era. The kinds of ships available even in say 1400 would be a poor bet for reliable transAtlantic crossings even by the "known" northern route, let alone striking across the middle of the North Atlantic in the lower latitudes leading to the Antilles. FWIW, if they gradually learned a lot empirically about Atlantic winds and currents, the way home again to places as far flung from each other as Norway to Iberia would be to join the Gulf Stream, which runs fairly close to a Great Circle route toward Britain--veering off one way on sea lanes well known in Viking times takes one to Norway, veering south, to France and Spain and Portugal.
Furthermore, consider the Norse accounts. The Norse were up in the north Atlantic. Newfoundland isn't exactly geographically well-situated for a shipping route between Spain and Japan (assuming no America), and it's hardly suited to support, by its own resources, the victualing needs of trading flotillas.
Actually if one picks up a globe and takes a look at it, the Great Circle Route from say Madrid to Canton runs--in its short part, inland along the Silk Route! The nearest passages by sea would, if only some kind of canal connected the Med to the Red Sea (and some form of low draft canal involving diverted river waters did exist from the Red Sea to the Nile in ancient times) run through the Med, into the Red Sea and Indian Ocean through the straits, around Southeast Asia to China and Japan from the south--indeed if one keeps going east instead of turning north at Vietnam, one is in the Spice Islands.
It was of course because the Ottoman conquest of Constantinople consolidated the power of the Sultanate and raised costs of goods imported the traditional ways that Europeans were looking for alternate routes, and again simply holding a globe in hand, a northeastern passage past Scandinavia and the White Sea along the Siberian Arctic coast would be a heck of a lot shorter than a "straight" shot to east Asia through some imaginary passage through any part of the Americas. It was impossible of course because of sea ice; if we can envision some climatic POD (which would consign it to ASB forum of course) making the Siberian coast navigable, then that would be the true alternate passage. Or a geographic POD (just as ASB of course) in which the coast of northern Asia receded far enough south to provide a navigable channel--we'd have to be careful not to wipe out Beringeria of course lest we prevent the colonization of the Americas.
Given the impassibility of the Northeast Passage, the choices boiled down to looking for some passage west past the Americas, hopefully indeed taking advantage of them for reprovisioning at the very least, or the Portuguese project of the Southeast Passage around South Africa into the Indian Ocean.
There is no deep geologic principle stipulating western continents as big as the two Americas have to extend so inconveniently from one set of iceberg-beset polar waters to the other without any breaks permitting crossing from Atlantic to Pacific. In fact the Central American isthmus formed only relatively recently geologically speaking; it would not be a tremendous geological POD to have OTL Panama or Oaxaca be an island-spotted shallow strait; this would suffice to keep the hydrology of the Gulf Stream largely operational while closely spotted islands could permit some exchange of fauna between north and south America, and yet ships of moderate draft could sail right through.
To get from Pacific waters just off Central America to East Asia is another hard trick, given the way currents and winds run one has to plunge through waters where islands are small and far between and keep sailing an awful long way even if one does have the luck and navigational skill to know where the islands are for reprovisioning. But having reached such locations as Melanesia, the Philippines or New Guinea, one can fairly easily then sail north and trade in Chinese or Japanese (or Korean) ports directly--if the respective Emperors of these strong realms will let you!
OTL in fact what Spain settled on was shipping silver (most valued by the Asian empires) and gold across the southern Pacific from Mexico to Manila, where Chinese traders would form the link bringing Chinese and other far Eastern goods to market, and trade the precious metals for these goods as well as filling out the galleon hulls with some Filipino craftworks and local produce, and then sail these Manila Galleons along the Great Circle which going eastward run with the currents, north right past the East Asian ports whose rulers would imprison them if they were in a good mood, or just kill them if not, on past the islands and peninsulas of northeast Asia (maritime Siberia) and south of the Aleutians and Alaska generally, to run into the American far northwest and turn south with the coastwise currents and winds past California back to Mexican ports such as Acapulco, which closed the circle. This circle trade in turn was routed on to Europe via the trade routes to Mexico; basically it turned Mexican and South American mined silver and gold into East Asian goods for the Spanish market. It was quite a good thing for Spain that Mexico existed to be plundered as well as serve as an intermediate provisioning point!
The moral of the story being that direct routes as the high-subsonic stratospheric jumbo jet flies (when indeed they too are not strongly diverted to handle jet streams!) are only sometimes of use and generally speaking just one way, due to the key importance of winds and currents. And yes, it would be nice if the sea route were not so long that reprovisioning need not be a thing, but since we are after all talking about global circumnavigation here, they are long and it is a bloody good thing there is somewhere to reprovision after all.
