Won't damage anything in the game, but not something you would leave up in real life. Obvious you can see with it underwater. Sometimes when I play with cams off I'll use it to watch for mines since we have no mine detection. Course you can watch dd's do runs on you.
Have you checked the fleetboat manual out. The real one, but answers most tech. question about all systems.
http://www.maritime.org/fleetsub/index.htm