First things first... where is the water coming from? Find the source and correct it and you won't have to come up with a way to add a drain pipe. I had a 1976 O'day 27 that had a loose strut that was leaking. It was under the gas tank and therefore difficult to diagnose but I could see water trickling in from under the tank. If it's just the stuffing box, maybe that needs to be adjusted or re-built. Are all the hose clamps on the engine tight and thru-hulls tight?