A few suggestions from my play this far. I'm sure most of them have been mentioned before
1) more flexible placement of secondary barbettes! This is a sort of minimum change, in general more flexibility of placement of everything, and more modular hulls/superstructure would be good.
2) some sort of system of morale, there's no way, for example, that a BB would continue fighting until sunk every time. Fire and damage near weapons should reduce effectiveness (of that weapon). High list should render the whole ship inoperable.
3) formations need a lot of work. Why does the lead ship randomly change after some damage? That should be a player decision. We need to be able to organise into divisions before battle. We need some formation orders (such as all ships in line turn 180 degrees) we need more sensible manoeuvres from one formation to another. Ships in formation should be able to manoeuvre to avoid torps or other ships, then rejoin.
4) fire arcs shown on battle map
5) compass around ship (toggleable)
6) how about the game shares successful human designs and uses them as ai designs?