How do you increase Naval capacity?

[Salem Graves]

I know there's some research for it, but it doesn't seem to appear nearly enough.. I have 32 naval capacity but my fleets are able to go up to 80, how can I increase my naval capacity??

[Stormsong]

Anchorages are a major source of naval capacity. You can also take Galatic Force Projection, though if I'm solely after naval capacity I'd rather take Grasp the Void. 5 full-on achorage starbases give more naval capacity than GFP does and it's not hard to reach 200 fleet capacity without GFP's help.

[Ruinous]

The trouble with 5 full-on anchorage starbases is they are vulnerable to being taken over and you also have the maintenance costs of the stations for that increase in capacity. You lose several and this can easily put you massively over your fleet cap and start to cripple the economy with the increase maintenance costs. Both GFP and Grasp are both a mid-game pick which is obviously obsolete as you move into the end-game, but can be very useful in actually getting you there. I play (and livestream) on ironman Grand Admiral difficulty and personally favour GFP as my third ascendency pick simply to help me survive the mid-game.
You do also get significant naval capacity from pops as well. In a large empire it isn't something to be sniffed at ;) Vassals and Tributaries also contribute capacity in this way with the right tradition pick unlocked.