I guess that before we move on from our discussion of fiberglass and composite boat construction that we should include a segment on a technique known as “Wood / Epoxy”. This is a building method that became popular in the late 1960’s with the introduction of epoxy based resins. This was at about the same time that production boat builders were making the switch from wood to fiberglass, utilizing mainly polyester resins as a building material. Until now most boats both production and home / custom built were constructed mainly of plywood, both in sheet form for hard chined hulls and various diagonal strip planking methods for curved hulls.
I remember that as a kid growing up on here in the north shore of Lake Ontario that wood boats were everywhere with sheet plywood and cedar strip being the most popular. Fiberglass was this wonderful new material that made for bright shinny curved hulls and sleek looking boats that almost overnight seemed to take over the lakes and rivers. For while wood was still popular with custom and home builders. It was at about this time that someone decided that it would be a good idea to cover these wooden hulls with lightweight spun glass cloth saturated with polyester resins. It seemed like a great idea at the time effectively turning the exterior surface of a wood hull into a hard piece of plastic. For a few years fiber glassing your wooden boat was the thing to do. It wasn’t a difficult process although a little messy and somewhat smelly. This went on for a few years until after some time boaters realized that the fiberglass cloth was delaminating from the plywood hull material. It was later determined that polyester resins, in damp conditions, over time will separate from plywood. So much for all the hard work. At about the same time Epoxy resins, even though they have been around since the 1930’s were beginning to show up as a boat construction material. Their increased cost was prohibiting them from seeing considerable use in production boats however with the custom and home builders who’s predominate material was still wood then began to utilize epoxy resins as a hull overcoat, both with and without light glass cloth re-enforcement. This was possible because of epoxy’s superior bonding strength to wood, it’s superior film strength and it’s superior hygroscopic properties. Remember a few posts back we learned about polyester resin’s hygroscopic properties, well epoxy is far superior in this regard. It does however have a couple of disadvantages. It degrades rapidly when exposed to UV and it also doesn’t like high temperature situations. This means that it makes a poor gel coat in that it must be over coated, preferably with a light colored paint or coating.
Lets’ now skip forward to a few months ago when I was contacted by a potential client to perform a survey inspection on his 26 foot wood epoxy Thunderbird sailboat. For those of you that aren’t familiar with the Thunderbird it is a 26 foot sailboat, designed by a naval architect named Ben Seaborn in 1958. It became incredibility popular with home builders in both North America and Australia as both a racing and cruising sailboat with one design racing fleets and an international class association. They were quite popular in my area here however the numbers have dwindled in recent years. As with many marine surveyors these days I generally shy away from wooden boats for obvious reasons but after a short discussion with the owner a few things came to light. The boat was constructed by the owner in 1977. The hard chined hull construction is GIS fir plywood sheeting over mahogany framing and the exterior hull surface is covered in light glass cloth saturated with epoxy resin. The hull interior is coated out in epoxy resin only.
I then decided to accept the assignment. At the inspection my findings were, that after 37 years of constant use, electronic moisture readings were not far off what I would normally see in dry plywood and percussive tests showed no structural issues. I found this very interesting that the plywood was in very close to new condition. I often inspect fiberglass boats that haven’t fared nearly this well. It looks like this epoxy is pretty good stuff. I guess that it’s just one of those things that just makes you want to go HMMMMMM now isn’t it?????