LOL!!!Reading an owner's manual BEFORE asking questions?? Preposterous!!
Leslie...may be the manual bilge pump outlet, mine has one, think it was an option...crawl under and see what's on the other side of the hole and what is connected to it (if anything)...Lol, I know, right. There is a 3/4 inch hole below the water line right by motor. It looks to have had something there before as there are three screw holes surrounding it. I have no idea what it is.