Currently there is only a single way to earn crafting experience and that is by making ships.
I propose that crafting be split up into five areas for earning experience. One would be able to choose a single crafting specialization and only be able to earn experience and advance in that path. It does not prevent you from crafting the default level 0 items of the other paths. You could reset your current specialization by paying a fee at the Admiralty in order to choose a different path which would wipe out all progress and experience in your current specialization. Each specialization would have seven levels of expertise in order to craft successively higher tier items. Choosing a crafting specialization would be optional.
The five specializations would be:
Shipwright - Shipyard, crafts ships
Naval Gunsmith - Forge, crafts naval cannons
Naval Academic - Academy, crafts skill books
Ship Outfitter - Workshop, crafts upgrades
Quartermaster - Storehouse (new building), crafts provisions, rum, rig & hull repairs - higher tier versions of these will enhance the effect, speed, and lessen weight
Each path as you gain higher ranks would increase your total labor hours.