I'd recommend adding private Shipyards the expand relative to the amount of revenue their company generates as well as the ability to buy and sell Shipyards for your own use.
The player can use them like regular Shipyards, but has to pay rent for them annually depending on their size, amount of slip ways, and if they are commercial or military. Civilians will also rent Shipyards to build there ships, so you actually can see where all the cities come from.
