Just signed up so I could post this here. This is the same issue I posted yesterday in the "Some feedback on the game" thread on the Steam forums. It makes more sense to report it here I think.
I also have a save file set immediately before the battle that causes this problem. (61 AI ships versus 23 of my ships.) I can send it to you if needed.
A large battle with say 80 ships should not freeze the game. I don't mind if it runs a bit slower or screen updates slow down to some extent. However it should not slow to 1 frame roughly every 30 seconds.
I tried the same battle with High quality graphics and lighting off. It made no difference, same as above.
Could there be an enemy AI issue in that enemies should not try to jam 60+ ships into one city? When I experienced this it was just myself (with half the cities) against one AI with the remaining cities. I noticed that the AI had no airships in most other cities (didn't check all), just a few buildings.
Is there a hard limit on the number of vehicles at a city? Maybe limiting it to 50 active at any time (total both sides) would be a workaround for now?
My system specs:
Desktop, Windows 7 64bit, Java 8, 3.3Ghz Dual core CPU, 8GB RAM, Nvidia GTX 960 4GB, multiple monitors. I play the game at 1920 by 1600 resolution, full-screen.
The same, rather hilariously, happened to me. Fortunately not to the extent that my game crashed, but enough to annoy the heck out of me, cause they never stopped coming.
This should now be fixed or at least much improved in v7.4.