how do vehicles work?

i can't for the life of me think of anything to possibly search for that brings up what should be a really simple question.

how does the stock vehicle system determine what tiles a certain vehicle can and can't cross? it's not like i can set tiles as water or not water. unless there's specific tiles which are always treated as water.... also what's the difference between the ship and boat and how does the system figure out what they can and can't travel across?

what terms are used to describe this? i just wanted a quick reference.... and all i can find are things about scripts you can add to have custom vehicles.

The boat is for shallow waters the ship is for deep waters. There is a  stock script called Game_vehicle that might have all the info your lookin for.

not really..... i mean. digging through the source isn't much better than just trying random things in the map editor.... i can't believe that there isn't just a simple reference explanation of how the system works somewhere.

so far my only guess is that the ship can go over basically all of the animated ground tiles. (Tiles_a1) and that the boat can go over all of them except the second one which seems to be the deep water one. i tested that and it seems to be true. the ship will go over any of the animated floors. and the boat will go over all except the second one. which is by convention i guess deep water. there are no shallow waters that the ship won't go over.

The only difference between the boat and ship is that the boat cannot enter deep water.

The boat and ship can travel in any body of water, as well as holes, the sky, and even lava.  You can even make it go over swap and ice if you change the passability to X.

Ships can cross anything on TileA1, boats can't cross the autotile which layers on top of the very first water autotile in TileA1 - which graphically, is the 'deep' water part.