There used to be nylon through hulls there. The nylon is not UV safe and they get brittle over time. The one on the left has broken completely off and is now just a hole in your hull. This would mean the thread stem and hose barb are still connected to the hose, however now they are discharging into the bilge.
The one on the right the external flange (mushroom) of the through hull has broken off, however the caulk is holding the threaded stem and the lock nut on the backside. This is good news, since that means the hose on the backside is more than likely also connected and discharging overboard.
These could be anything that needs to drain overboard: Bilge Pump discharge, locker drain discharge, cockpit sink, etc.
Determine the size and replace with Marelon. Bronze and stainless are more expensive options. stainless introduces some issues where when water is introduced to an oxygen deprived space, SS will rust. (Think screws and bolts in deck plates and stanchions).