For the hull of the canoe, we took last year’s canoe length and geometry into account while making our own adjustments. We wanted to balance maneuverability and speed, and through research decided on a canoe length of 16 feet. We gathered information to learn how different geometries would affect the canoe’s performance in racing conditions and applied the knowledge to our final design to meet our primary focuses. Some of these geometry considerations and their effects include:

• V-shaped keel: improved primary and secondary stability
• Short length: more maneuverability, less material used
• Asymmetrical design (centroid is not central): increased forward speed
• (Small) rocker: better tracking, simplified construction
• Sharp entry line: increased speed

We decided to take a completely different approach to our canoe mold this year, which meant that we could not take as much guidance from previous years’ solutions. We wanted our form to be reusable as well as recyclable, so we did not want to use polystyrene foam. To make the form itself reusable, our team came up with a modular design that allowed small sections to be de-molded individually and screwed back together if needed. We also considered spacing between sections to give team members access to the form while placing concrete. We CNC’d the canoe’s shape into each section according to our SolidWorks design. We then connected the cutouts of each section with hardboard, which was able to bend to the canoe’s curvature.

We tested wood as a primary material by successfully building a singular section of the proposed mold. From there, the team prototyped and tested the design of the overall mold until the final canoe design was completed. One issue we had to consider was that once the canoe was poured, it would sit in the form in a 100% humidity room for 1 week to cure. To prevent the wood of the form from warping, we decided to cover it in polyurethane, which proved to be successful in a test where a prototype was stored in a 100% humidity room for 7 days. We covered the hardboard on the inside of the form in a layer of plaster followed by vinyl to ensure easy demolding from the concrete. Our team decided on these materials early in the design process by testing the demolding of Quikrete on an array of different substances. 

Our concrete mixes were based somehwat on last year’s designs but adjusted to fit our own specifications. Two lightweight concrete mixes were designed and proportioned to fit the structural and aesthetic needs of the canoe. ASCE limited the proportions and contents of the mixes for the competition.

First, we separated the aggregate into #16 and –#16 using a screen shaker to utilize all sizes of our lightweight aggregate across both mixes. The structural mix was designed to have the lowest unit weight, as it would make up the most volume of the canoe. Our team continued the tradition of using a plastic mesh as reinforcement in the middle of the structural layer to increase the tensile strength and therefore the maximum bending moment of the canoe. The aesthetic mix, used just to coat the structural layer, was designed with a white cement base so that it could be pigmented to display our chosen color scheme. We ran and tested our mixes at Martin Marietta multiple times to hone the workability, strength, and unit weights of each concrete mix as well as to practice batching, mixing, and admixture dosing.

Last year’s canoe was slightly unstable because it was very buoyant. To fix this issue, we wanted concrete mixes with higher unit weights, so we decreased the proportion of smaller particles. However, we did not consider these increased unit weights in conjunction with increased thicknesses; instead of spraying on the concrete like last year, our team wanted to hand-place the concrete due to concerns with constructability regarding the use of the spraying mechanism. Our choice to hand-place the concrete resulted in layers that were thicker than intended. The thicker layers resulted in a much higher canoe weight than anticipated, which we counteracted by adjusting the bulkhead size accordingly.

We mainly used hand calculations to carry out structural analysis on the canoe. We created shear and moment diagrams to illustrate loading cases for the race scenarios (2 paddlers, 4 paddlers) to find the maximum shear force and the bending moment of each. For the sake of the calculations, we estimated that the uniform distributed weight of the canoe was 31.25 lb/ft and that each rower was 200lb.

After we weighed the canoe (4 team members stood on scales, recording their change in weight when all holding the canoe together), we performed buoyancy calculations to determine the needed volume of the bulkheads. We found that about 2.6 cubic feet total of polystyrene foam was needed to bring the total unit weight of the canoe to 60 pcf, which is less than water (64 pcf). The foam was divided between the two ends of the canoe to be bulkheads, shaped to fit, then covered in a thin layer of yellow aesthetic concrete to bind it to the canoe.