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The Ponderosa was designed to handle both static and dynamic forces induced by competition racing.To resist these forces, the canoe was modeled with fiberglass mesh reinforcement, high-strength/low-weight concrete,and custom hull characteristics.
Due to the nature of this competition, the hull geometry was pre-specified by a National Concrete Canoe Committee. Therefore designing the hull meant electing a thickness and adding optional ribs, thwarts, gunwales, etc.After comparing various desired qualities from canoes built in previous years, a unanimous hull thickness was established at ½”.Also incorporated into the design were two ribs, located seven and fourteen feet from the bow, gunwales, and bulkheads on both ends.
To design a mix that would enhance a high strength to weight ratio, multiple mixing materials were researched.First, each concrete mix that was created by a nationally qualifying team (in 2009 & 2010) was recorded in a spreadsheet.Based on desirable properties, a list of common materials was compiled and acquired. Twenty-five combinations were mixed and measured for slump, luster, and strength.Upon comparison, a final mix was determined with the following properties located in Table 1.0.
The reinforcement material and design was similar to that of the 2010 concrete canoe team. The abundant of excess reinforcing material left by the 2010 team was enough to fulfill the structural requirements for this years’ design (assuming cracked concrete).Recycling it also succeeded our effort to implement a green process.The design consisted of two layers of 4.3 oz. fiberglass mesh, spaced 3/16” and 1/8” from the concrete exterior.
To accurately analyze the canoe for yielding stresses, a series of modeling programs were utilized and compared with hand calculations to validate all results.First, a boat analysis program called Prolines was used to find hydrostatic forces acting on the hull. Then a model was generated in SAP 2000 (NAU licensed finite element program). The hydrostatic output was inputted directly into SAP 2000 and bounded at the bow/stern. To simulate the canoe in equilibrium, two point loads of 330lbs each were applied at 7 and 14 feet from the bow.The 330lbs represents the average weight of a male (200lbs) and female (130lbs), combined as a total of 4 people.A comparison of the SAP 2000 outputs and hand calculations verified that the stresses were accurate and far less than the materials yield stresses.