Is it me, or is maintaining a navy in M2 and Rome completely not worth the cost? The upkeep of even as small as five ships is likely more than what is lost in the rare occasion when a port is blockaded. Troop transportation and destroying ships carrying enemy units are both good uses, but that also is too rare to justify the cost in my eyes.
Though there was a time when I slew 60% of Scotland's armed forces and their king by sinking a transport with a full army. Only has happened once, though.
I don't know about Rome, but for me in MTW2, maintaining a large navy is important, or at least till you gain total control of the sea, and especially in the Mediterranean. Usually the enemy you are at war with 2 or 3 nations plus pirates who, while independently are meek, their combined strength and the scattering of their ships in various places makes army transportation via ships a saliva-swallowing feat.
By having a large navy (About 10 ships) enables you to fight enemy ships without losing so many sailors that the navy need stop at every port to recruit new sailors because after the intial attack, your fleet might not have enough men to survive a second or third one.
5 ships can beat 3 ships with ease. But can it defeat 2 more squadrons of three?
Perhaps it is because you are playing a North/Baltic Sea nation and don't fight off that many naval countries. In the North Sea, there is only England, Scotland and Denmark (France's navy is usually concentrated in the South). In the Baltic only Russia (who I never see build more than 3 ships ever) Denmark, Poland and to a very small extent HRE.
But in the Mediterranean you face Milan, Venice, Papal States, Spain, Moors, Egypt, Turkey, Sicily, HRE, France, Byzantine Empire and if you include the Black Sea, Hungary. And the Italian states really like ships.
Thats 3 vs 4 vs 13