Sounds like a drain hose from the molded lip which holds the edge of the engine cover? I noticed mine had two small holes draining water into a void which eventually worked its way back to the bilge. My hull does not have as much fiberglass on the aft end of the bilge platform area like yours does (yours seems to be sealed on the aft end). I think my bilge is relatively open on as it heads aft under the floor. Perhaps they closed it up and added a drain pipe after they got into the 500's. Just a guess.