Plastic ring = thru hull?
If your 28.5 is like my 86 at the bottom of my anchor locker is a white plastic thru hull fitting, which my appear like a plastic ring. This fitting is connected to a hose which drains rain water from the anchor locker to a hull fitting just ( 1 foot) below deck level on the port side. On the inside of the boat in the front V berth there is a 6 inch "inspection port" which can be removed to gain access to the entire assembly. I would recommend checking this out before you have a rain water collection in this area. Any 1/2 inch thru hull fitting would be an acceptable replacement.