In all honesty though, I believe that boat hitching is possible from any port in the world. SF might be a bit large and chaotic, try a smaller city, and look for private boats rather than barges. A lot of boats will probably leave from farther south as well, might want to head down to Sandiego, probably a lot of surfers turned yachters there. Try to find the book "A hitch hikers guide to the oceans", has a lot of good information about boat hitching.