[thevardanian]

A lot of early voyages funded by the various crowns was actually put under extreme secrecy so much so that many sailors would only later be told of the real voyage...

At least that's what I recall reading awhile back. If anyone could corroborate that would be nice.

[mannykannot]

The value of secrecy in matters of commerce and state has probably been recognized from the get-go. Beyond that, nobody thought sailors had much in the way of rights; in 1571, almost a century later, there were tens of thousands of galley-slaves on both sides in the battle of Lepanto.

https://en.wikipedia.org/wiki/Galley_slave#Europe

Unfortunately, I don't know anything about what Columbus's crews were told. It does seem they were free men (four of whom signed up in return for an amnesty) and were paid:

http://www.christopher-columbus.eu/ships-crew.htm