I have a new (used) Avon inflatable. We took it out for the first time and learned a lot! While we were washing it down we discovered a hole in the floor at the stern in the aluminum floor. It basically allowed 15 gallons of water to go into the keel. We were really unclear as to whether this should have been an inflation point, or if there should be a plug. It was even suggested that it was suppose to take on water as 'ballast'. It was a 'nice' whole with a hard plastic/rubber grommet. Any thoughts?