Islander 28 thruhull fitting?
I have a steel fitting with a large wing nut tightening it into the hull in the bilge. The fitting is 2+" in diameter and has a plastic insert that is secured by a pin. The inner plastic plug is made watertight by two O rings that are spaced about 1/3 of its length from each end. The outer end of this plastic insert is flush with the outside surface of the hull. If it were not facing horizontally I would suspect it of being a depth transducer face. This assembly is mounted in the bilge and is about 6" above the top of the keel. I have two spare plugs for this fitting. I am guessing it is a garboard plug. It is not at a low point in the bilge.
Can anyone tell me what this is?