Definitely needs to be replaced with a bronze or filled in (a new idea that just entered my mind) so there is no chances for leaks. It is for the sink which is why it is so low. A "galley" in a 23 footer is a joke if you ask me. Risking sinking a nice sailboat boat with a possible a leaky thru-hull, just to say I have a sink, makes no sense to me.Yikes! That's a plastic thru hull below the waterline. Maybe a previous owner installation. You might want to replace it with a bronze thru hull. Perhaps it is for a sink?
I understand that the thru hull would be above the waterline at rest, but when sailing, it would be below the waterline for sure. For that reason alone, I would not want a plastic thru hull.That is a drain for the aft starboard lazarette that is designed to be used as an ice box or cooler. the drain is above waterline, and it is unlikely that it would require replacement with a bronze fitting. The drain in my OD26 has functioned fine for 37 years. You may be able to gain access to the drain by removing the sliding gally unit and crawling aft (not sure about that one!).
The cooler drains to the thru-hull in the back of the cockpit right next to the main cockpit drain so this must be for the sink.I understand that the thru hull would be above the waterline at rest, but when sailing, it would be below the waterline for sure. For that reason alone, I would not want a plastic thru hull.