Kevin, observers are randomly assigned swapped at the captains meeting between boats (of similar size to the extent possible) and they are with the same other boat for the entire tournament, so the observer of the team you are randomly assigned to goes to your team's boat. They aren't on different boats each day.
The observers job is to do exactly that, observe. you cannot help with the fishing in any way, you make sure the team plays by the rules and you record the fish caught on the official score sheet, including the exact GPS coordinates species and approximate size of the fish. Since the tournaments are no cull, all tournament legal fish must be kept. If a borderline size fish is caught, you have to make sure the fish is measured before they toss it back.
That's about it, it is a great learning experience.
Tim