Back when I documented my boat, 1988 you had three choices.
1. The CG district you where in, in my case Philadelphia
2. Where the boat was actually kept, in my case Rock Hall, MD
3. Where you live, in my case New Hope, PA
I chose my home, New Hope, PA, as the hailing port as I didn't want to go through a paper work thing every time I moved the boat and Philadelphia seemed a bit broad as a location in that I live about 45 miles north of Philly and Rock Hall is about 70 miles south of it.