1. Layered Fiberglass vs. Injection Molded Fiberglass Surfboard Fin Finite Element Analysis
1st Progress Report
Dan Ippolito
Project Advisor: Ernesto Gutierrez-Miravete
Rensselaer Polytechnic Institute
October 17, 2011

2. Layered Fiberglass vs. Injection Molded Fiberglass Surfboard Fins Deflection Comparison Analysis
A deflection comparison analysis is a study of two or more components in which displacements, as a result of an applied load, are compared
When identical loads and boundary conditions are applied, a comparison of flex patterns can be done by observing the x, y and z displacements throughout the geometry of the components
To do a detailed deflection comparison finite element analysis should be uses to plot displacement contours to visualize various deflections
The goal of this analysis is to investigate how different the flex patterns are when a surfboard fin is constructed of layered fiberglass vs. cheaper injection molded fiberglass

3. The Project
Model a surfboard fin as accurately as possible in Abaqus CAE
Make two identically shaped, and meshed, fins and assign one isotropic material properties and the other layered orthotropic material properties with alternating fiber angles
Apply a force to the fins exposed surface and secure the base of the fin plugs
Run an Abaqus FEA analysis and compare deflections throughout the fin for layered fiberglass vs. the injection molded construction
Injection Molded Fiberglass Fin
Layered Fiberglass Fin

4. Fin Geometry and Model Development
To make the fin’s part geometry a popular thruster center fin (a FCS® model G-AM) is modeled as a solid part in Abaqus CAE. This is done using a picture of the fin as well as the actual fin to scale the part accordingly
Since layered fiberglass must be assigned Lamina material properties, and are not suitable for solid parts, a shell made is made using the solid fin model
The shell is assigned various thicknesses to map the thickness contour of the solid fin. This shell model will be used for both the isotropic injection molded fin and the orthotropic layered fiberglass fin to provide an accurate apples to apples comparison
Picture of the FCS® G-AM Center Fin
Abaqus Solid Model of the FCS® G-AM Center Fin
Abaqus Shell Model of the FCS® G-AM Center Fin
Abaqus Shell Model of the FCS® G-AM Center Fin with Thickness Contour Shown

5. Assigning Material Properties
Assigning different materials properties to each of the two fins simulates the different construction methods
One fin is assigned isotropic elastic material properties, for injection molded fiberglass, and different shell thicknesses to different geometric regions to provide the thickness contour
The other fin will be constructed using a composite layup in which elastic orthotropic fiberglass material properties are defined. A composite layup is assigned with defined thicknesses and alternating fiber angles of +45°/-45°
Abaqus Shell Model of the FCS® G-AM Center Fin
Material Properties for Orthotropic
E-Glass/Vinylester Fiberglass
Material Properties for Isotropic
Injection Molded Fiberglass

6. Derivation of Drag Pressure Applied to Fin Exposed Surface
Calculation of Drag Force for a Full Speed Bottom Turn
The drag force is calculated for a full speed bottom turn on a wave that is 10 ft high assuming you are traveling the same speed as a vertical drop from that height
Derivation of Drag Pressure Applied to Fin Exposed Surface
A Surfing Bottom Turn
Drag Force Equation

7. Preliminary Results of Isotropic Injection Molded Fin
Expected Outcomes
It is expected that layered fiberglass will behave differently that injection fiberglass when loaded. How different these flex patterns are is what this study is aimed to find
In general, a fin with a stiff base and flexible tip is ideal for performance
Preliminary Results of Isotropic Injection Molded Fin

8. References
[1] Ronald F. Gibson “Principles of Composite Material Mechanics”, second edition, CRC Press Taylor & Francis Group, 2007
[2] White, Frank M., “Viscous Fluid Flow”, 3rd Edition, McGraw Hill, 2006
[3] Chou Shih-Pin, “Finite Element Application for Strength Analysis of Scarf-Patch-Repaired Composite Laminates”, Master of Science Thesis, Wichita State University, Dec. 2006
[4] Stephen Pirsch, “How to Build Your First Surfboard – Glassing”,
[5] M. Nurhaniza, M.K.A. Ariffin, Aidy Ali, F. Mustapha and A. W. Noraini, “Finite Element Analysis of Composites Materials for Aerospace Applications”, Nov 2010
[6] Y.W. Kwon, D.H Allen, R. Talreja, “Multiscale Modeling and Simulation of Composite Materials and Structure”, 2008