Monday, January 28, 2008

Epoxy Debate

Yesterday I posted links to online boat-related discussion forums I like to read. The Wooden Boat forum, associated with the magazine, Wooden Boat was at the top of the list. This forum is full of informative posts related to wooden boat building. On the forum you'll find builders of just about every kind of boat imaginable that can be made of wood, from the modern composite racing craft to replicas of tried and true working vessels of the last and prior centuries.

With so many builders of different boats, disagreement is bound to emerge, and when the subject of epoxy comes up this is always the case. I take an interest in these discussions about epoxy, because so much of my boatbuilding and other woodworking depends on it. I first started using it for laminating wood around 1991, when I began building my own double-bladed kayak paddles out of red cedar, ash, and mahogany. The paddle shafts and blades were constructed by gluing together many layers of thin strips of these materials sawn on the tablesaw and then glued up into a block roughly the dimensions of a paddle. Shaping was done with various power and hand tools, and after hours of hard work a fine paddle with feathered blades offset to 90 degrees was the result. I used these paddles for hundreds of miles of kayak touring, and never had a failure.

My next test of epoxy as an adhesive was in 1993-94, when I took an interest in traditional archery and began making wooden longbows, many of them laminated with a layer of planed bamboo on the back, which is the high tension side away from the shooter. I built several bows like this with draw weights of up to 80 pounds. If there was ever a test of an adhesive, the rigorous tension and compression cycles that a glue line is put through when a bow is drawn and then suddenly released is among the most extreme. Like the paddles, I never had a failure of an epoxy glue joint in any of my bows.

From paddles and bows I went on into wooden boat building, beginning with a 19-foot woodstrip canoe that eventually evolved into a decked sailing trimaran canoe with two 15-foot woodstrip outriggers. This type of construction depends on a layer of 6-oz. fiberglass cloth laminated on both the interior and exterior of the hull to reinforce the wooden shell, which is made of red cedar and cypress strips only 1/4 inch thick. In this construction there are no internal frames or ribs to hold the hull in shape or to strengthen it - only the epoxy saturated fiberglass. The result is a stiff, lightweight hull that never leaks or loses its shape. This first canoe I built, Seldom Seen, is as structurally sound and beautiful today as it was when I launched it in 1995.

I could go from here, describing everything I've built with epoxy since, from wooden bathroom showers to more than a dozen stitch and glue plywood boats. Suffice to say, I'm a believer in epoxy. Modern epoxy resins make it possible for those of us willing to experiment to create incredible composite structures using wood, the most beautiful of all natural materials, in ways never imagined before. Those woodworkers and boatbuilders unwilling to use it out of some resistance to modern technology have no idea what they're missing.

Back to the Wooden Boat Forum debate that inspired this post:

This was started by someone who read a dire warning in one of Larry Pardey's books about the use of epoxy as an adhesive in wooden boat building. Most anyone who has had an interest in sailboat cruising has heard of Lin and Larry Pardey, the famous cruising couple who built their 24-foot Lyle Hess designed wooden cutter, Serafynn by themselves and then circumnavigated in her. They later built a 29-foot version of the same type of heavy monohull cutter which they named Taleisin. The couple has rounded Cape Horn and made many ocean voyages on this boat as well, and they've written of their exploits in many books and countless magazine articles. Their experience gives them great credibility among all of us who sail and build boats. But the Pardeys interest in boats is focused on heavy, traditional wood construction using traditional methods that predate the development of materials like epoxy resins and fiberglass cloth. These methods are just as valid today as they were a century ago, but their validity does not change the fact that modern technology can also produce sound boatbuilding methods. The problems seem to arise when someone attempts to misuse a new technology, by combining it with an older method that was never intended to depend on such a modern adhesive. The Pardeys distrust of epoxy stems from seeing failures of it when applied improperly in this type of heavy, traditional wooden boat construction.

In this older method of boatbuilding, you're dealing with larger, heavier timbers that make up the hull components. These designs depend on precise carpentry joints reinforced with fasteners to keep them in place. More massive pieces of wood expand and contract to a greater degree when going through cycles of wet and dry and hot and cold. And the wood components of these traditional hulls are subject to this expansion and contraction because such hulls by design are not waterproof without caulking between the hull planks. It's the old basket vs. wooden bowl analogy, in that the basket (traditional wooden boat hull) depends on swelling to keep it watertight. Haul a planked wooden boat like this out of the water for an extended period of time and the planking will shrink, leaving gaps in the joints. In order to float, this type of hull depends on swelling of the wood and the individual parts must work independently; hence the need for fasteners that hold them in place during this cycling. Most any glue, including epoxy, will fail if used in an attempt to join large timbers subjected to this kind of cycling.

This is the reason modern wooden boats designed for epoxy construction are built in a completely different way. Scantlings and joinery methods are optimized for the use of epoxy as an adhesive if the designer understands the material. This is how the modern epoxy composite boat resembles the laminated wooden bowl, as opposed to the woven basket. The hull is made up of smaller parts that do not move independently, but instead are rigidly joined together to form a monocoque structure. In most designs using this type of construction, the hulls are further sealed and waterproofed by a laminated sheathing of fiberglass over the exterior. Water does not penetrate to the wood and there is no possibility of swelling due to water intrusion. The hull will be stable and stay the same whether the boat is in or out of the water.

So the bottom line is that if used as it is intended, epoxy as an adhesive and a laminating resin is without equal. The problem arises when someone tries to use it in a way that is less than optimum, such as in traditional boat construction, inviting failure and causing them to believe that the epoxy is at fault. If you want to build a modern wood-epoxy composite boat to a proven design, don't be discouraged by these naysayers. Epoxy is incredible stuff and I have absolute faith in it. Just look at the hundreds, if not thousands of boat designs that depend on it. Boats like Wharram's Tiki designs are engineered for epoxy construction and nothing else would work, nor could you build the boat as designed with any other type of glue. I have complete trust in the integrity of the Tiki 26 hulls I am putting together without metal fasteners of any type and I won't lose any sleep worrying about a glue failure when I'm on a passage days away from the nearest land.

If you want to read the arguments on both sides, the link to the forum debate about epoxy is here:

1 comment:

  1. I enjoyed your comments and explanations about epoxies. I have built 2 bats so far and am quite the novice. I am working on a bigger one. I just enjoyed looking through your blog.


"A boat is freedom, not just a way to reach a goal."
Bernard Moitessier - A Sea Vagabond's World


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