1) Start off with a new map, make it small around 75x75, but I don't think it matters.
2) Use the Max elevation button.
3) Paint water over all the map
4) place some boats. I used longboats
5) use the max button 3 or more times (until you can't see water just the terrain underneath)
6) Paint the terrain underneath anything you want.
7) Use the Min button until there is no more water and boats are on land
8) move a boat around. It moved on mine. You can also place any water unit, but cannot place a land unit, so the terrain acts just like water.
I playtested and the boats COULD NOT move. And when you go back into the editor the boats cannot move any more and you have to repeat the process. So bassiclly there is no use for this, except to place water units on land, and it's also interesting to know. Also if you adjust the terrain in the editor when they can move, it stops them from moving.
(_̅_̅(̲̲̲̲̲̅̅̅̅̅̅(̅_̅_̲̅marij̲u̲̅an̲̅a̲̅̅_̅_̅_̅()
(is not as helluva drug as pepe)