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Wooden Boat Project Report School of Engineering Grand Valley State University EGR 365 Fluid Mechanics Project Section 905 Instructor Dr Mokhtar August 5 2021 Introduction 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 best to start with studying the design of such object and start with a prototype Prototypes are quicker 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 three conditions that must be met are the geometry kinematics and dynamics must scale appropriately at 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 familiar with the forces acting on the boat also known as buoyancy drag and lift and tipping moment induced Any object in water has a buoyant force acting upon it The buoyant force is equal to the weight of fluid being displaced Whether the object floats or not is based on the weight of the object as seen in figure 1 Figure 1 Buoyant Forces on an object Subsequentially if the object weighs more than the buoyant force it will sink If the object does not sink the depth at which the object sits in the water is known as the water line Less dense objects 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 the case due to drag and lift forces The wind will cause the boat to go forward some but soon drag forces will increase and the boat will go at a speed slower that the wind The best way to sail is perpendicular 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 large than 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 boat The reason this phenomenon works is due to the sails making an airfoil shape The inside of the sails has a high pressure at the center of the sail While the outside has a low pressure causing lift The forces acting on the sail are large due to a large surface area In order for the vessel to not tip over the center of gravity of the vessel must be relatively low and the keel must counteract the side force induced by the lift and drag Once all the side forces are balanced the only resultant force 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 a righting moment To achieve a righting moment the center of gravity of the boat must be lowered closer to the water line This is achieved by adding weight to the keel and possibly increasing the length of the keel The rudder of a boat helps with some side forces but is often just used for just steering Turning the rudder helps turn the boat at a given yaw angle Then the rudder is turned it creates drag and side 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 12 th scale model of a recreational sailboat capable of holding two to four people In doing so the user can learn about model design and predict 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 designed to be bulbous since it has good aerodynamic properties The drag is less and the bulbous keel allows for keel weight to be added This in return adds better stability when force is applied to the sails and helps lower the center of gravity The jib sail helped create more lift for the sailboat and resulted in a faster hull speed The rudder was designed to help with side force since during competition an extra sail was added on the front The keel worked great turning the boat and had no 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 square inches Using the calibrated data on strain vs gram drag The stain on the hull can be converted into grams of drag and then lbf respectively Using the data above the following table can be made Table 1 Hull Data Speed ft min 10 20 30 40 50 60 70 Drag lbf Reynolds 0 00545 0 01196 0 01754 0 02220 0 02778 0 03522 0 03615 13202 36586 26404 73173 39607 09759 52809 46346 66011 82932 79214 19518 92416 56105 Drag Coefficient 0 71089 0 38989 0 25411 0 18082 0 14482 0 12751 0 09616 Froude Number 0 03217 0 06435 0 09652 0 12870 0 16087 0 19305 0 22522 Friction Coefficient 0 01668 0 01279 0 01111 0 01012 0 00943 0 00893 0 00853 Residual Coefficient 0 69421 0 37710 0 24299 0 17070 0 13539 0 11859 0 08763 Analyzing the data shows that concepts were true and followed real world results As speed increased 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 the hull 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 Froude number increases residual coefficient goes down This is good and shows the vessel is approaching hull speed Residual Coefficient vs Froude s Number r C 0 8 0 7 0 6 0 5 0 4 0 3 0 2 0 1 0 0 0 05 0 1 0 15 0 2 0 25 Fn Figure 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 Coefficient of Drag vs Yaw Angle 10 20 30 40 50 60 70 80 90 Yaw Figure 5 Coefficient of Lift vs …

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