Re: Found this loose in the bilge, transducer?
It's a transducer for the fish finder for sure.
Two options:
1. Reinstall it to "shoot thru the hull" (if not aluminum hull). Look for a spot where it may have been previously -- some sort of glue, epoxy, caulk, etc. where it was stuck down. When reinstalling be sure to get ALL air pockets out of whatever you use as glue. Some suggest silicone as it's easy to pull it back up if need be (e.g. if you're not getting good readings at speed).
2. Could it have been transom mounted (and subsequently just thrown in the bilge)? Look for a bracket or holes on the outside of the boat near the bottom of the transom. Reinstall depending on what you find.
Or, if you have the $$ and want to replace it with a better\newer unit just do that. Easy install just follow the instructions.
Good luck.