As always, rename the ztd extension at the end of your file's name to zip and extract.
Find your ucs file and edit it with Notepad.
Find the section with the heading: [Characteristics/Integers]
For underwater, add in the line below:
cUnderwater = 1
For floating, add in this line below:
cSurface = 1
Save and exit Notepad. Go into the main directory with the folders Scenery and Objects. Zip both of them up in the same zip file. Rename zip at the end of the file to ztd.
You're done.
