You can modify the GC2Types.xml file to make hulls whatever size you wish. Make a copy of that file, edit it, then place it in, for example,
C:\Program Files\Stardock\Total Gaming\GalCiv2\DarkAvatar\Mods\Default\Data
Enable mods through the game setup and specify the Mods directory. Don't edit the stock file in place or you won't be able to play Metaverse games with your installation. If you do that, you'll get a warning when attempting a Metaverse game and if you post it, it will be disqualified with a cheat flag. To correct the problem, you would have to restore the original file (reinstall) then start a new game.
Hope that helps.