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| Stitch-and-Glue Boatbuilding ADVANTAGES: The differences between conventional plywood-on-frame and stitch-and-glue construction are significant. To better understand the differences between the two, contrast the structural dissimilarities of an early biplane and a modern jet airliner. The biplane was made up of frames and spars over which was stretched a thin skin. The jet airliners structure, on the other hand, is much simpler, with a stressed aluminum skin rigidly attached to bulkheads and spars to create a single unit. A boat built by attaching plywood planking to lumber frames is most similar to the biplane; a stitch-and-glue boat more closely resembles the jet airliner a homogeneous structure in which the skin bears the primary stresses. The basic argument for stitch-and-glue construction is that it uses fewer parts and that epoxy is used to bond and seal the parts to achieve a stronger, monocoque (one-piece) boat. The initial construction is quicker and easier, uses fewer parts, and requires no building molds. And in the long term, the boat is much easier to maintain. Almost all boatbuilding methods require expensive tooling. Production fiberglass boats have their elaborate plugs and molds. Traditional plank-on-frame or cold-molded wooden boats require complicated building molds. This expensive tooling generally stops much of the evolution of an individual boat design. Stitch-and-glue construction does not bear this initial burden. With no building molds or tooling to consider, a stitch-and-glue design has a chance to constantly evolve and improve and that's important. There are ways to increase the ability of the stitch-and-glue boat to suit its purpose and meet owner’s performance requirements. CONSTRUCTION: Stitch-and-glue construction is technique using marine plywood, baling wire, fiberglass tape, fiberglass cloth, epoxy fillers, hardwood flour and epoxy resin. The basic steps for the builder are to cut out the two bottom panels, the side panels and the transom. These parts are then stitched together with the baling wire along the panel seams. The wire holds the panels together until the epoxy mixture is cured, then the wires are removed. The epoxy is thickened with the fillers or hardwood flour and then applied to the seam in a thick, continuous bead over which layers of fiberglass tape are applied. Each layer is completely applied. Once this is cured the hull is turned over, the wires are removed, the chines are radiused and the entire exterior of the hull is sheathed with fiberglass cloth using the epoxy resin to completely saturate the cloth. The key to the method is that all of the structural surfaces must be saturated with the resin. Using marine quality materials will ensure a quality product. One nice thing about stitch-and-glue construction is that fewer tools are required compared to other methods of construction. Stitch-and-glue construction allows the builder to once again utilize the strength and beauty of wood while eliminating the negative maintenance problems so prevalent in the past with wooden boats. LOFTING: In sewn-seam construction, several building basics or norms are altered. First, there are no building molds required, no complicated lofting of molds or support structures are necessary. Second, the lofting required is not to draw a full size picture of the lines of the boat, but to draw a full-size picture of the parts. For a simple V-bottomed boat, the parts required for a basic hull are two side panels, two bottom panels, and a transom. A panel-projection drawing is scaled out so that it fits on flat sheets of plywood. If we lay out that sheet of plywood horizontally in front of us, the left edge or small edge is the station baseline. All stations are measured out from that edge parallel to each other at a fixed interval. In our example the station space is 12", so every 12" for the length of the panel a straight line is drawn perpendicular to the baseline, or long edge. When those lines are drawn and labeled, the actual offsets can be drawn in. The bottom long edge of the panel is our baseline, and a tape measure can be hooked over that edge and pulled out alongside the station line, measured and marked. The rule in lofting is feet, inches, eighths. If a dimension says 1-10-4, then that translates to one foot, ten inches, and four/eighths, or one/half inch. A dimension that say 2-4-0 is two feet, four inches, and zero eighths. Once all the points are marked onto the plywood panel you can connect the dots with a long, fair batten and cut the parts out. This essentially is all the lofting needed for you to start construction and you are free to concentrate your energy on building the boat.
Excerpted from www.devlinboat.com |
