Classic plastic and the ravages of time.....
Since there are few (if any) systems on board of a vessel that can be counted upon to keep functioning reliably for more than 20 years (or even 10...) NO 1979 vessel is inherently seaworthy; unless practically every appendage, component, accessory and -- yes -- even the hull itself has undergone regular inspection, maintenance and upkeep.The latter may involve complete replacement, e.g. when involving standing and running rigging. However, after 20 years even the chainplates are suspect. Also, don't forget that none of the sealants, caulks and glues available in the late seventies (with the possible exception of PDMS) compares favorably to the superglues and supersealants of today. However, even todays polymeric materials are unlikely to last 20 years without degradation of many mechanical and chemical properties. In other words, pretty much any seam, joint or frame that is glued or sealed may have to come off and be redone with fresh sealant, caulk or glue. The fact that the fiberglass hull may (notice: MAY) still be in a good enough shape is one of those incredible strokes of luck. Off all the materials the first builders of "plastic composite" boats could have chosen, they just happened to chose the one that was able to withstand the marine environment better than nearly any other material known to man today (if taken care of properly). If not for that lucky choice older plastic boats all around us might be falling apart faster than termite-infested wood! In conclusion, there is nothing wrong with planning to cross oceans in 20-year, or even 30-year old fiberglass boats. Just don't expect all 20-year old vessels of any given brand to pass inspection anymore than all 50-year old men and women can run the marathon......So, John Cherubini is absolutely right: PREPARATION is the key. As long as you do realize that preparation of a 20+ years old vessel may sometimes require almost as much work as building a new vessel from scratch.Good luck!