Whenever someone uses the tideconfigs "maxTide" and/or "minTide" in any mapconfig, boats refuse to drive since the last A3 update. This is relevant for any usermade maps, like mine "Distrikt 41 - Ruegen" and can be replicated by using those tide-mods that change these values for vanilla maps (see links to workshops below).
Boats will just start rotating their motors, but not move any bit. Even teleporting, moving them under water or spawning them in the air changes anything.
Looks like since the update boats dont check anymore for the actual waterlevel, but look for the vanilla level and pretend to be flying and therefore refuse to move.