Switch to dev branch since it has all achievements fixed unlike the main game. Because single developer could not thoroughly test the fixes he wasn't confident enough to publish newest version as regular release. During my tests however I can report test build is as stable as vanilla.

1. Right-click on Capsized in your Steam library, followed by Properties...
   
2. In new window click BETAS
   
3. Select dev - dev from the dropdown on the right

This will apply automatically and update will start. Close the window now.

Another crucial reason we are doing this is for game to start using new savegame format which stores information in human readable plain text, easily modified by anyone.

If you made progress in vanilla game it will be ignored by dev version, same for config options. Fortunately starting from scratch does not make much of a difference. Btw if you wish to continue old progress simply opt-out of BETAS (None in dropdown), your progress will wait for you.

Save is just 1 small file stored in \Content\Config.cfg (Config.xfg in main version).
If it's not there - run the game once, configure options if you wish and then exit.

1. open Config.cfg and find this line
   
   <DuelMatches>0</DuelMatches>
2. replace 0 with 1

1. open Config.cfg and find these lines (12 total)
   
   <COOPBeaten>false</COOPBeaten>
2. replace false with true

Once changes are made, save and close Config.cfg, then run Capsized [dev]. To actually trigger the achievements you'll have to beat 1st mission (CRASH SITE) again. Two minute job on Easy.