@Treva : the accent is there in game, but I don't now how to make it with my keyboard here.
Thanks for the pesado correction.
Limit is half of the actual number of ships, same as for land units, half of the actual number of regiments.
The big factions such as France or Britain don't really have a limit for the main ships, like the 74. The limit is much more important for smaller factions, or for the bigger ships like 122-guns.
Keep in mind that this is the total limit, it will be spread between different regions. So if they are captured, you will have a reduced limit.