If your template passes over an obstacle, you roll an Attack die and suffer damage on a hit.
If your ship stops on an obstacle, you roll an Attack die and suffer damage on a hit AND you lose your attack that round. It's under the section on Obstacles as I recall. I've double-checked it a few times as it's always been a fuzzy distinction for many people.
Huh. FOr whatever reason, I remembered it was lose an action, not lose an attack. Good to know.
Whoops, looks like I forgot to specify that. Yes, you lose your action too, same as with overlapping.