Alaska has more coastline than the rest of the United States combined and more then half its costal cities are unreachable by conventional road. For this reason, in 1960 (just one year after statehood) Alaskan voters approved a bond issue to initiate a State-owned Alaska Marine Highway System . AMHS started with one vessel M.V. Chilkat and in 1963 were added three more. Nowadays AMHS has nine vessels. First the system operated from Skagway, Haines and Prince Rupert, today is included more than 34 ports from Aleutian Chain on the west to Bellingham in "lower 48".
Estimated 400 000 passengers and 100 000 vehicles travel the Alaska Marine Highway annually.
My experience
I took the last ferry in 2000, 22th September. From Seward. The voyage to Juneau took two days. I was waiting here one day for my connection to Bellingham,WA, and this second voyage took other four days. Tickets costed $149 and $225 without room. A bed costed about $20 per a day. You can use a sleeping bag in After viewing Lounges or in "solarium" - covered shelter on upper deck. Here you can also break a tent. But the tent can not be in covered area. It is a beautiful view from here and because just a few older people come to here it is also place where youngish are...
Other places that we stopped were - Valdez, Yakutat, Sitka, Petersburg, Wrangell (totem's pole), Ketchikan (totem's pole of Tlingit, show,...). We stay usually from one to five hours . Somewhere that is enough but sometimes it is very short. All cities are very small and in some case you have to take a cab or bus to the village because ferry terminal could be pretty far away from the centre.