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Wooden Boat Project ReportSchool of EngineeringGrand Valley State UniversityProjectEGR 365 – Fluid MechanicsSection 905Instructor: Dr. MokhtarAugust 5, 2021Introduction:The design of a vehicle, aircraft, or vessel is troublesome when where to start is unknown.Instead of wasting valuable time, resources, and money trying to come up with an idea, it is bestto start with studying the design of such object, and start with a prototype. Prototypes arequicker, easier, cheaper, and just as accurate as the real model. The fluid effects on a 1/12th scale vessels are true for the following conditions. The threeconditions that must be met are the geometry, kinematics, and dynamics must scale appropriatelyat constant ratio. This means the prototype will match the model to a T if done correctly. In order to build a watercraft vessel, as required for this project, the user must become familiarwith the forces acting on the boat also known as buoyancy, drag and lift, and tipping momentinduced.Any object in water has a buoyant force acting upon it. The buoyant force is equal to the weightof fluid being displaced. Whether the object floats or not is based on the weight of the object asseen in figure 1.Figure 1: Buoyant Forces on an objectSubsequentially, if the object weighs more than the buoyant force it will sink. If the object doesnot sink, the depth at which the object sits in the water is known as the water line. Less denseobjects will always float on a denser fluid. Many believe in order to get a sailboat to sail forward, it must go with the wind. This is not thecase, due to drag and lift forces. The wind will cause the boat to go forward some, but soon dragforces will increase and the boat will go at a speed slower that the wind. The best way to sail isperpendicular to the wind. Since the sails can be moved at an angle relative to the wind direction,it will create drag and lift forces. The lift on the sail helps the sail boat move forward if it is largethan the drag. The figure below helps demonstrate how it works due to vector notation.Figure 2: Lift and Drag Vectors acting on the sail of a boatThe reason this phenomenon works is due to the sails making an airfoil shape. The inside of thesails has a high pressure at the center of the sail. While the outside has a low-pressure causinglift. The forces acting on the sail are large due to a large surface area. In order for the vessel to not tipover, the center of gravity of the vessel must be relatively low and the keel must counteract theside force induced by the lift and drag. Once all the side forces are balanced, the only resultantforce left are a large lift and small drag force causing the vessel to move forward. As stated previously, the center of gravity must be low and the keel must help stop side forces.The tipping of a vessel is known as a tipping moment and the balancing of this is known as arighting moment. To achieve a righting moment, the center of gravity of the boat must belowered closer to the water line. This is achieved by adding weight to the keel and possiblyincreasing the length of the keel. The rudder of a boat helps with some side forces, but is often just used for just steering. Turningthe rudder helps turn the boat at a given yaw angle. Then the rudder is turned it creates drag andside forces that help turn the boat. Since these vessels are unmanned, everything on the boat will be set in place and observed. The purpose of this project was to design and build a 1/12th scale model of a recreational sailboatcapable of holding two to four people. In doing so, the user can learn about model design andpredict the performance of the prototype from the model. Below shows the model made for analyzing.The model had an angled mast just for looks along with the front railing. The keel was designedto be bulbous since it has good aerodynamic properties. The drag is less and the bulbous keelallows for keel weight to be added. This in return adds better stability when force is applied tothe sails, and helps lower the center of gravity. The jib sail helped create more lift for the sailboatand resulted in a faster hull speed. The rudder was designed to help with side force since duringcompetition, an extra sail was added on the front. The keel worked great turning the boat and hadno problems at all. All design choices were made from research, videos, and pictures/layouts of other sailboats. Model Analysis:The first analysis done on the vessel was the hull test. This test required getting the wetted area,waterline, and the hull pull test. The water line was 10 inches and the wetted area was 41 squareinches. Using the calibrated data on strain vs. gram drag. The stain on the hull can be convertedinto grams of drag and then lbf respectively. Using the data above the following table can bemade.Table 1: Hull DataSpeed(ft/min)Drag (lbf) ReynoldsDragCoefficientFroudeNumberFrictionCoefficientResidualCoefficient10 0.00545 13202.36586 0.71089 0.03217 0.01668 0.69421200.01196 26404.73173 0.38989 0.06435 0.01279 0.37710300.01754 39607.09759 0.25411 0.09652 0.01111 0.24299400.02220 52809.46346 0.18082 0.12870 0.01012 0.17070500.02778 66011.82932 0.14482 0.16087 0.00943 0.13539600.03522 79214.19518 0.12751 0.19305 0.00893 0.11859700.03615 92416.56105 0.09616 0.22522 0.00853 0.08763 Analyzing the data shows that concepts were true and followed real world results. As speedincreased, the drag, Reynolds number, Froude Number went up. Respectively, the drag, friction,and residual coefficients went down. The Froude number depicts the vessel was approaching thehull speed since the number started to go up when speed went up. Figure 4 below shows the correlation between residual coefficient vs. Froude number. As Froudenumber increases, residual coefficient goes down. This is good and shows the vessel isapproaching hull speed. 0 0.05 0.1 0.15 0.2 0.2500.10.20.30.40.50.60.70.8Residual Coefficient vs Froude's NumberFnCrFigure 4: Residual Coefficient (Cr) vs Froude Number (Fn)Sail data was provided, but the calculating lift and drag from the sail data needed to be analyzed. The two test that needed to be done were calculate drag vs. yaw angle and calculate lift vs. yaw angle.0 10 20 30 40 50 60 70 80 9000.20.40.60.811.21.4Coefficient of Drag vs Yaw AngleJibslot = 1.25Jibslot 1.25Jibslot = 1.3125Jibslot = 1.3125Yaw (°)Coefficient of Drag (CD)Figure 5: Coefficient of Lift vs. Yaw

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