Old dogs, new tricks ....
Galileo’s proposal — Jovian moons
In 1612, having determined the orbital periods of Jupiter’s four brightest satellites (Io, Europa, Ganymede and Callisto), Galileo proposed that with sufficiently accurate knowledge of their orbits one could use their positions as a universal clock, which would make possible the determination of longitude. He worked on this problem from time to time during the remainder of his life.
To be successful, this method required the observation of the moons from the deck of a moving ship. To this end, Galileo proposed the celatone, a device in the form of a helmet with a telescope mounted so as to accommodate the motion of the observer on the ship.[6] This was later replaced with the idea of a pair of nested hemispheric shells separated by a bath of oil. This would provide a platform that would allow the observer to remain stationary as the ship rolled beneath him, in the manner of a gimballed platform. To provide for the determination of time from the observed moons’ positions, a Jovilabe was offered — this was an analogue computer that calculated time from the positions and that got its name from its similarities to an astrolabe.[7] The practical problems were severe and the method was never used at sea. However, it was used for longitude determination on land.
But I was never lost with my sextant, a good compass, and a good time hack.
Never mind all this, my LORAN is not working!
When he did his PowerPoint for the Portuguese, they of course immediately picked up on this error. After all, the Portuguese knew that Eratosthenes had figured it at 25,000 miles in the 3rd CBC and that Chris had made a basic "units" error in his calculations. Not good.
The other thing was that he was a foreigner and the Portuguese also figured he could be a spy for the Genoese traders who wanted to sent the Portuguese on a wild goose chase based on this screwy data, so they could corner the pepper market or something like that.
In Spain, he was able to sell his wrong idea better because, instead of having to explain it all in Latin, he could present it in his native Genoese dialect, which of course is Catalan, and thus easily understandable to Ferdinand and Isabella. Also they were not as technologically hip as the Portuguese anyway. (The Portuguese tell "Polish" jokes about Spaniards to this day.)
"The rest," as Sherman used to say, "is history."