From Bellingham in Washington state, the ferry takes a gentle three days or so chugging north past Canada. It is called the Inside Passage because for most of the journey you are not in open sea, with a view of beautiful forested hills, snowy mountains and glaciers. The M/V Kennicott (among other boats) calls at Ketchikan, Juneau, Haines, Skagway. There are other routes to Sitka, near Anchorage and the Aleutians. Would recommend spending your money on a cabin with a BIG window.
www.akferry.org/
en.wikipedia.org/wiki/Alaska_Marine_Highway
Google map: tinyurl.com/2wb8d2m