Epoxy Barrier coat
What is Interprotect but an epoxy layer? It sounds like whatever epoxy was put on your hull simply doesn''t have a fancy marketing name. Despite fancy names and advertising, epoxy (like gasoline) is epoxy. If you''ve got a layer of it, it doesn''t matter who made it. If there aren''t any blisters now in a 1981 boat, it sounds like you''re trying to fix a problem you don''t have. Get some new sails instead, you''ll have more fun.