About differential naval movement, I can't say anything except that coastal tiles cost three movement points, sea tiles two, and ocean tiles and port cities one, and studying your ship's route to move it through the cheapest tiles (for example, the two ocean tiles south of Machu Picchu) is important, if a PITA.
The basic principle of ship chaining is that a ground unit which still has movement can transfer from one ship to another in the same tile at no cost in MP, and so can move much farther in a given turn than one ship could take it. As an example--which will involve some arbitrary assumptions, since our chain is imperfect at the moment
--the cav unit now in a Carrack in Medina could take that ship to the nearby stack of two Carracks; get on one of those and sail to Paris; disembark, cross France, and board an imaginary Carrack at Rheims; take that, exploiting the presence of the two ocean tiles in the area, to the stack of two Carracks off Niagara Falls; board one of those; and finally, if the last two Carracks in the chain still had their movement, land on Germany's desert/saltpetre tile, all in one turn. The fundamental idea is that we should reinforce our now-distant fronts like this, not by the excessively slow procedure of just loading Carracks up on our continent and sailing them to the active theatres. Even if your operation of the ship chains is less than ideal, it'll be a lot faster than that. A two-turn rhythm, in which the ship chain lands units on one turn and resets on the next, is acceptable.