We left Gustavus in heavy fog on the day we were scheduled to enter the Park. You have to be in by 10:00 AM and you must check in by VHF radio when you are crossing the border of the Park on your way to Bartlet Cove where all private and tour vessels must check in in person. The big cruise ships have a different procedure, but only two of those are allowed in each day, in the summer only. The fog did not let up until we were well into the Park and in sight of Bartlet Cove. Raven is now equipped with radar, and AIS (Automatic Identification System) for other vessels that carry the transponder, and both of these are displayed on the GPS based chart plotter. This is a mariner's miracle if there ever was one. You can "see" other vessels and even see their name, course, and speed if they have AIS, and position your boat in safe water on a chart. You must be very careful in fog, but it's not the nightmare it used to be. Just before we broke out of the thick fog in the Park we were greeted by something I have never seen before, a fog bow. It looks white but has very faint rainbow colors .