by Philip Jacobs
My first exposure to lightweight, plywood boat building was at an MCA builders show several years ago. Bob Brown and a group of informally recruited volunteers wire-tied 3 or 4 plywood panels into the rough shape of a canoe in what appeared to be a matter of minutes. Compared to building strongbacks and forms, then fitting some 60 cedar strips plus trim, plywood construction is fast!
About a year ago, I began to find catalogs from companies offering kits, plans, classes, and supplies for this type of kayak construction, along with associated Internet web sites (Chesapeake Light Craft at 410/267-0137 or HYPERLINK http://www.clcboats.com; www.clcboats.com; Pygmy Boats, Inc. at 360/385-6143 or HYPERLINK http://www.pygmyboats.com; www.pygmyboats.com; Volkskayaks at 902/542-3244 or HYPERLINK http://www.valleyweb.com/whynot; www.valleyweb.com/whynot; Kayak Buildersí Resource Page at HYPERLINK http://www.guillemot-kayaks.com/Building/Building.html) www.guillemot-kayaks.com/Building/Building.html).
The more I looked into this type of building, the more resources I found, including an MCA kayak plan (The Simplicity), local sources for marine plywood, magazine articles, and books in local libraries and bookstores.
Typical construction begins with curved panels carefully cut out of thin, marine grade plywood. Small holes are drilled along the edges of the panels, allowing them to be drawn together with short lengths of twisted wire (stitches), and pulled into compound hull shapes. Beads or fillets of thickened epoxy (glue) are applied to permanently join the edges, which are then reinforced with fiberglass tape and resin.
Many designs are built without the aid of forms or molds, although some use temporary forms during assembly, and others incorporate form components into permanent bulkheads or reinforcing members. Larger boats, using thicker plywood or members, may be partially nailed (tacked) together, and even some lightweight boats may be nailed at places such as the kayak deck seam, which is notoriously difficult to tape on the inside.
I read descriptions of stitch-and-glue and tack-and-tape building (along with every possible permutation of these terms - tack-and-glue, stitch-and-tape, . . .), sewn-seam construction, and the most colorful and provocative term, tortured plywood. Although many builders, enthusiasts, and vendors appear quite willing to use these terms interchangeably; others, predictably, drew sharp distinctions. One company went to great lengths in their literature to assure potential buyers that their boats were not tortured.
Of course, boat builders are not without their opinions, and few are reluctant to share them. I canvassed several of the sources noted above, along with a number of books, and came up with surprising consensus on terminology, if the methods of construction can be separated from the finished form; a hull with complex, and often compound, curves.
When forming these curves with narrow pieces of cedar, as in MCA strip construction, the many joints between strips help the pieces to conform to the hull shape with a minimum of twisting, allowing the use of regular wood glue and light clamping pressure. As the width of strips or panels increase relative to the radius and complexity of the curves, increased clamping pressure and glue strength is required to make flat pieces conform to the desired hull shape. For a kayak, this may require a single panel to bend at several locations, and in different directions, at the same time, resulting in what is referred to as compounded or developed plywood.
The various methods of stitching and tacking are used to either temporarily or permanently hold the plywood panels in the desired hull shape until the glue and/or tape and resin cure. In practice, multiple methods may be used on different portions or phases of a boat's construction (and we haven't even started talking about clamps yet), and the methods used may or may not influence the final hull design or shape.
The key area of contention appears to be distinguishing the point at which the plywood becomes tortured, with general agreement being that the larger the size of individual panels, the more complex the final panel shapes, and the greater the amount of force required to create a desired hull contour in those panels, the closer it comes to tortured status. Additional numbers of panels may be used to achieve a desired hull shape with less force or internal stress, but with additional chines. Smoother, more rounded hull shapes may require more assembly force, with more internal stress created in the panels.
As with other areas of boat building, there will always be preferences and opinions regarding methods and terminology. Many home built boats will be construction hybrids, as a practical matter, with improvisation leading to continued innovation. Unless one is interested in construction details, or in sparking an extended debate, it may be simpler to describe a boat by the outcome (e.g. ì . . its a multi-chined, plywood, sea kayak with a narrow entry and a minimum of rocker . . .î) rather than by its method of assembly; after all, the proof is in the paddling.
Philip Jacobs
