Ambreville
Deity
If you use two calendars this should effect the movement of all units, for example playing as Spain, it took me almost one year to sail from Barcelona to Turkey, as was 11 moves = 11 months. If you play week calendar then you will navigate only 11 weeks = 2,5 months, a more logical period for those times. Same as to the La Macha Canal, you should be able to go back and forth 4 times in a month, and not 1 month to go and month back.
The speed of units in CIV has always been artificial and not at all realistic, especially when it comes to ships. Once they are underway, sailships really only need a few days to sail from Spain to Turkey in the real world. Allowing 2.5 months is laughable!
This is a problem that surfaces in many scenarii. Take for example Age of Discover, where it takes years to cross the Atlantic. The issue here is playability. If the real ship speeds were employed in the CIV game relative to a calendar, in most cases these ships could effectively move anywhere on the map each turn. The real issue is whether ships encounter contrary winds at departure, which determines whether they leave at all. Once they leave, they can always tack to catch the right winds.
Gamewise, this is a problem. For land units, the problem isn't the same as land units have to deal with terrain and enemy areas of control (etc).
"La Macha Canal" -- do you mean the Channel? (La Manche).