blisters, boat hull that is
While osmotic blistering can occur on fiberglass boats of any vintage, the worst blistering problems gnerally occur on boats laid up between the mid- 1970''s through the eary 1980''s. The reason generally cited for this period is that resin formulations were altered during the fuel crisises of the 1970''s. You never even heard discussions of this problem until the late 1970''s. But by the early 1980''s the problem was understood and supposedly formulations were changed and barrier coats became more common as well.
This does not mean that you can''t find boats with blisters that were constucted after this period. And there are some manufacturers that do better than others. Some of the French builders, Beneteau and Jeaneau, had a problems with blisters in the late 1980''s and early 1990''s for example.