Yeah, it's a bit convoluted. I forwarded your sentiment to the community teams. In the mean time if you go into %userprofile%\Documents\My Games\GalCiv4\Designs you can manually delete the designs you want to get rid off permanently.

I see a lot of the 'Devs know about the issue', but basic stuff like this shouldn't still be a problem 2+ years after release.

Solution: Obsolete ships never come back on reload. Create a button to restore obsolete ships in the options menu or shipyard (because mistakes happen). QoL improvements is GalCiv 4's best friend. :)

Part of the problem is the game is designing ships for you every turn. So you can hide it and research a few techs and the game designs another variant for it. So its not a simple solution since the game isn't tracking which of the its designs you've hidden. You can use the user filter for ships to not see all the AI designs.

However, temporarily hide this design should work for custom designs. Obsolete is still session based. I did share this with the community team in April.

Problem with that is that all the ships coming back are all my custom designs. So unless it also try to update MY custom ships, that doesn't track. Also...even with what you said, the solution is still simple; Simply don't update/design anything based on the already obsoleted design.

Also, slightly related. Please do make sure to swap the texts between the "Obsolete" button in Shipyard screen with the "Temporary hide this design" in Ship Design screen. If you swap the two of them, it make MUCH more sense (ignoring the inability of the obsoleted designs to stay obsoleted after reload).