itch.io

Sounds like your version doesn't have passability yet.  Open the sample maps, then database, then tileset, right click on the tileset listed there and copy.

Then go to your game, create a new tileset slot and paste it there, or paste over your existing ocean tileset.  Make sure you've added all the tileset images to the img/tileset folder in your game and you should be good to go!  This version has all the settings configured for you so you shouldn't need to take any further action.