Mold Construction: the Design for Our Canoe Was Rendered Using Solid Edge. the Program

Mold Construction: The design for our canoe was rendered using Solid Edge. The program runs on Microsoft Windows and provides solid modeling, assembly modeling, and drafting functionality (Siemens 2015). After determining the final shape, our 2013 team generated full-scale computer cross sections at 30.48 cm (12 in.) intervals along the length. Then they used the drawings to produce plywood templates and mounted and aligned them on a wooden strongback.

They constructed a male mold by first nailing 6.35 mm (0.25 in.) thick luan strips to the cross sections over the majority of the length and then fitting foam blocks at the bow and stern. After placing a fiberglass layer over the strips and blocks, the team progressively refined the shape. They worked under subdued lighting so that spotlighting could be used to identify problem areas. These were marked, filled with drywall, and sanded until all discontinuities were removed (Team UAH 2013). Last year’s team refined the bow and stern sections to improve the hydrodynamics of their entry (Team UAH 2014).

Both teams had difficulty removing their canoes from the form and spent considerable time retrofitting the bow and stern sections with flotation. They also found it difficult to contour reinforcement in these areas. We removed these sections from last year’s form and duplicated the shapes using flotation materials so that they could be cast directly into our canoe. We used the remainder of the form to save time and as part of our sustainability effort.

The bill of materials included on the design drawing (see page 11) lists the materials used to produce the form. We added the photographs around the border to illustrate and clarify our teams’ construction techniques.

Core Construction: Our plan was to design and build a reinforced core to accurately position our primary reinforcement, reduce the overall weight of our canoe, and help us maintain structural integrity. We began core construction by producing a 6.35 mm (0.25 in.) thick flotation frame. This was done by placing 3.8 cm (1.5 in.) wide Cellular PVC stringers in the transverse direction at 38.1 cm (17 in.) intervals along the length of the mold. We fabricated several longitudinal stringers by first soaking 3.8 cm (1.5 in.) wide pine strips in water and then contouring them to the mold. After notching and gluing the transverse and longitudinal stringers together, we added diagonal members consisting of 2.54 cm (1.0 in.) wide balsa strips.

Canoe Construction: We began concrete canoe construction by draping a sheet of plastic over the mold to which we applied turtle wax and a mold release compound. We initially attempted to construct our boat by placing a layer of C-grid directly on the mold followed by the flotation frame. We used a steel mesh in the bow and stern sections because the mesh could be more easily contoured to the shapes.

During concrete canoe construction, we prepared several premixed batches of our concrete mix. During this process, we used a mechanical mixer to achieve better homogeneity and reduce the water content, thereby strengthening our concrete. We also timed the delivery of constituents, selected the proper mixing tools, and adjusted the mixing speed so that materials were dispersed evenly. We used a wire whip and high speed mixing to prevent our cementitious materials from clumping, thereby preventing dry particles from forming within the cement paste. For safety, we prevented microspheres from becoming airborne by mixing them with SBR latex, and used a low shear attachment to prevent breakage based on recommendations from the manufacturer (3M 2015b).

Once the concrete was ready, some of our team members used drywall knives to level it to the upper surface of the flotation frame. After stapling the outer layer of C-grid to the frame, we secured 2.36 mm (0.093 in.) diameter wires across the grid at 15.2 cm (6.0 in.) intervals down the length. Then, we used drywall knives to level the outermost layer of concrete to the upper surface of the wires. After an hour or so, we removed the wires and filled the grooves.

Our plan called for removing the boat from the mold within 24 hours so that we could place the inner layer of concrete and add concrete reliefs. But when we did so, the inner layer of C-grid and the flotation frame flexed, causing the outermost layer of concrete to delaminate from the reinforced core.

This failed attempt created a one week delay during which we spent a great deal of time and effort removing concrete from the flotation frame and bow and stern sections. We also strengthened the frame to prevent flexure during form removal and revised our construction scenario.