Dear Mother, From your picture it appears to be a PVC/Plastic hull fitting with a chrome covering that has peeled off the other two seems to be doing the same just not as bad. The easiest correction would be to replace the hull fitting with a new stainless fitting. Marine Hull Fittings can be purchased from any marine supplier or can get on line (amazon) most are in the $20 dollar range.
Good luck on the fix. Bob