My experience with heavy thick fog was a number of years ago on my buddies Mirage 33. We were sailing out of Halifax Harbour to a small harbour just down the coast. As soon as we got to the mouth we entered a fog bank. Without radar or a chart plotter, we went on dead reckoning using a compass, paper chart and listening to the waves smash agaiint the granite cliffs in the distance. Did pretty good...heard the sound of the buoy we were looking for and then the compass to set a new course. Once we got into the small harbour the fog lifted and we were happy to see land. Now....even with my handheld Garmin loaded with Blue Chart, I avoid fog like the plague.