Solar Boat Hydrofoils Design Team Jackson Betro, Kristen Fassbender Scott Kilcoyne, Kyle Machuta Design Advisor Prof. Gregory Kowalski Sponsor NU Solar Boat Abstract The Northeastern University Solar Boat team requested a hydrofoil to attach to their current boat to improve performance in the Solar Splash World Championships. Critical design considerations for competition include dimensional limitations, such as a maximum width of 2.4 meters, and static hull stability. Primary goals include dynamic stability, integration with the current boat, and a sprint performance improvement of 3 seconds per 300 meters. Based on analysis with a variety of software packages, the team selected an aluminum surface-piercing, V type hydrofoil in a split tandem configuration with an inverted front set of foils. A transient model of the boat simulated various scenarios and provided numerous outputs, including hull displacement, speed, and stability. The results verified that the hydrofoils exceed the design requirements. The superstructure, connections, and hydrofoils all passed stress analyses to ensure successful implementation. Boat with Hydrofoils Glides above Water at Speed Hydrofoils For more information, please contact g.kowalski@neu.edu 120
The Need for Project Hydrofoils provide the Solar Boat club a chance at winning the Solar Splash World Championships Northeastern University Solar Boat is an interdisciplinary club that teaches students fundamental skills in project management and engineering. By having a successful competition record, the club may attract more members and encourage students to apply their skills outside of the classroom, while reflecting well upon the university. Implementing hydrofoils gives the club a chance to win the Solar Splash World Championships (Rep. 4.6). The Design Project Objectives and Requirements The hydrofoils design Design Objectives objective is providing the Solar Primary design goals include dynamic stability, integration with Boat club with a successful the current boat, maneuverability, and performance improvements solution to reduce drag and leading to better overall placement in the competition. Previous improve competition capstone groups optimized the hull and drivetrain designs. To date, the performance. club s best overall performance was 10 th (Ref. 3). To make winning more viable, the capstone group will reduce drag by implementing hydrofoils. Design Requirements Solar Splash rules require boats meet dimensional constraints and stability testing (Ref. 6). The Solar Boat club expects hydrofoils to provide performance improvements of 3 seconds per 300 meters in the Sprint event of the Solar Splash World Championships. Design Concepts Considered At each stage of the design process, the team investigated several alternatives. Decisions included hydrofoil placement, type, and material. Hydrofoil Placement The location of the center of mass of the boat determines the distribution of wetted foil surface between the forward and aft of the boat. The hydrofoils provide a lift that is proportional to the foil surface within the water. A centrally-located center of mass requires a tandem foil arrangement, in which the foil surface amounts are symmetrical at the front and back. Meanwhile, the conventional arrangement features greater foil surface to the front of the boat and accommodates a forward center of mass, and the canard arrangement features greater foil surface to the back of the boat for a backward center of mass (Ref. 17). 121
Figure 10: Three Main Hydrofoil Types (Ref. 13) Hydrofoil Type Three main hydrofoil types exist based on a literature review: the surface-piercing V or U type, the surface-piercing ladder type, and the submerged foils (Ref. 13). Figure 10 illustrates the three types. Within the surface-piercing V or U shape, the orientation of the V, amount of foils, span of the foils, and connection at the vertex may vary. Each design variation provides unique attachment challenges, lift to drag ratios, and manufacturability considerations (Rep. 4.4). The ladder type requires definition of the angle of the ladder, the amount of foils, and the distance between foils. The submerged foils may have varied attachment and programming. All hydrofoil types contain the following variables: angle of attack, chord length, span, and hydrofoil profile, or shape. The surface-piercing designs boast the benefit of self-regulating lift as the foil surfaces breach out of the water. If the boat tilts, the foils to the tilted side become more submerged than the other side and provide more lift, stabilizing the boat. The submerged foils require movable elements or flaps to adjust lift. Additional Design Considerations Within all mentioned designs, certain fundamental parameters drive the effectiveness of the hydrofoils. The angle of attack affects the lift to drag ratio and the likelihood of cavitation, which is the development of bubbles caused by low pressure along the foil surface (Rep. 4.4.7). The foil profile affects the lift, drag, and the ratio between the two forces (Rep. 4.4.2). The angle of the foils from the horizontal allows for modification of the vertical lift. For example, a horizontal foil provides more vertical lift than a foil set at an angle, which splits lift between the vertical and horizontal components. Material While a variety of materials may have been sufficient for the foils, fiberglass and aluminum were investigated based on availability and familiarity. Epoxy resin would bond with the fiberglass to a foam or 3D-printed foil core. Recommended Design Concept 122
The selected design is a surface-piercing V shape hydrofoil with split tandem arrangement and an inverted front foil set. Design Description The surface-piercing foils provided the desired inherent stability, and the V shape design minimized the necessary component attachment points and avoided the difficult angled attachment to the hull (Rep. 4.1.1). Tandem arrangement of foil surfaces accommodates the central center of mass. Separating the V at the vertex facilitates attachment given the improved performance of foils spanning the width of the boat (Rep. 4.4.4). Inverting the front foils to make an upside-down V reduces negative interference caused by undesirable downwash flow at the rear foils (Rep. 4.4.5). Figure 11: NACA 8-H-12 Foil Profile (Ref. 31) An angle of attack of two degrees avoids cavitation, while providing a competitive lift to drag ratio (Rep 4.4.7). The NACA 8-H- 12 foil profile, shown in Figure 11, provides an asymmetry that further benefits this ratio without negative effects (Rep. 4.4.2). An angle of 30 from the horizontal, or 120 between the foils, provides adequate vertical lift while minimizing the effect of horizontal lift on the support structure of the boat. Vendors stock aluminum foils and foam bases in NACA profiles, such as NACA-0012 and NACA-8-H-12. Aluminum provided a higher safety factor than fiberglass (i.e. 1.48 compared to 1.01), while also ensuring a higher quality surface finish and profile shape than fiberglass (Rep. 4.7). Figure 12: Top-Level Simulink Model Analytical Investigations While decision matrices drove some design decisions, software packages such as 3DFoil and ANSYS provided the basis for the more technical design comparisons (Rep. 4.1, 4.4, 4.7). Following design optimization, MATLAB s Simulink extension facilitated development of a transient model of the boat, as shown in Figure 12, based on a flowchart of variable interrelationships and outputs from 3DFoil and Orca (Rep. 4.6). The model helped validate the effectiveness of the foils by analyzing scenarios with and without the hydrofoils to determine performance improvements. Keeping the forces on each foil separate allowed for stability analysis given a tilted boat. Key Advantages of Recommended Concept 123
Figure 13: Inverted Front Split V Hydrofoil Design The inherent stability of the selected design, shown in Figure 13, provides a significant advantage in balancing the boat without pontoons. The transient model shows that hydrofoils provide a performance improvement of eight seconds in the Sprint competition, which would put Northeastern University in first place in the Solar Splash World Championships (Rep. 4.6). Financial Issues The total cost of the one-off hydrofoil set and related provisions was approximately $2,000. Based on the hydrofoils unique implementation onto the club boat, the hydrofoils present an isolated financial investment. The club required software to properly analyze foils, and the selected Hanley Innovations 3DFoil cost $395 (Ref. 25). All other costs applied to producing the physical hydrofoil system. The set of 6.25 x 10 foil extrusions from Vortech, Inc. cost $1,390 (Ref. 31). Materials for the attachments and support structure were approximated to be $200. Shipping and packaging costs were neglected, along with the costs of available materials within the club cage or capstone lab. Recommended Improvements The suggested improvements target the changeable nature of the boat from year to year, by leaving the exact placement of the foils flexible for the boat s variable center of mass. Future iterations that may benefit hydrofoil implementation include the vertical placement of the foils with respect to the hull and the exact location of the foils with respect to the center of mass. Currently, these parameters remain relatively undefined based on the variable nature of the boat from year to year given modifications by the Solar Boat club. The hydrofoil and attachment structure design accommodate such variations by being relatively adaptable. The foils attach to a T slot channel, which allows foil adjustment forward and aft, while vertical adjustments may be done at this connection or at the vertical portion of the foils. As the center of mass changes from year to year, the club will need to determine, analytically or empirically, where to place the foils for best performance. To improve the foils, the weight, span, chord length, angle of attack, and attachment may be further optimized based on performance. 124