Big ships are simply far more useful. Galleys are mostly for buffing your numbers and for being cannon fodder for transports and big ships. Even in the med. the galleys aren't that useful.
Edit: Oh yeah, make sure to keep an admiral around even if he's 0/0/0 as having one attached to your army increases positioning. Before the patches positioning was so overpowered that 10 carracks could beat 50, but it's toned down a bit more. Keep your navy size smallish though, don't go beyond 50, make a second navy instead.