For any of us that sail around Portsmouth there has always been a fine line on the chart off the shore of Southsea that runs out to Horse Sand Fort. This minor detail relates to the submarine defense wall. Wonder what happens if you hit it? We know of a visitor to the UK who hit it at 7 knots and immediately stopped. We understand that the metal hull & keel had to have very substantial repairs in Portsmouth and that the family crew was rattled. It’s a feature that is easily missed on our Solent charts.