Personally, I neglect my navy in the first 20-25 turns as I like to enjoy peace with other factions for a while, focusing first on rebels. I do not try any alliance though. This is total war, isn't it?

After that, AI usually starts its foolish attack and blockades my ports. Then, unfortunately, upgrading my cities has taken most of my money, so I go for a minimal navy, which does not take a lot in upkeep.

The drawback is that the AI seems not to do such a bad job and keeps pounding my small fleet until it is sunk. AI does not blockade a specific port consistently, but it nonetheless keeps randomly blockading one/a few of them. Is that a smart technique to deny a counter-attack or pure randomness?

Anyhow, is it only my feeling or the casualties in naval battles are tuned down when compared to MTW or RTW? Now, I can actually win naval battles (H/VH) without overkilling strength ratios.