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Yacht Design Technology

Introduction. How do you compare different yacht designs?How can you determine which is best?What are the criteria for

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Yacht Design Technology

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    1. Yacht Design & Technology Performance Evaluation

    2. Introduction How do you compare different yacht designs? How can you determine which is best? What are the criteria for best?

    3. Tools of the Trade Velocity Prediction Program (VPP) Race/Regatta/Event Modeller

    4. VPP Input = Boat parameters Solves for: boat speed associated heel angle range of true wind speeds and headings adjusts trim and set of sails for maximum speed Output = Yacht performance polar plot

    5. VPP - Input Boat Parameters: Physical characteristics of the hull & appendages Dimensions of the rig and each sail in inventory Details of the drag-only elements (windage)

    6. VPP - Input Boat Parameters: Physical characteristics of the hull & appendages Dimensions of the rig and each sail in inventory Details of the drag-only elements (windage)

    7. VPP - Input

    8. VPP - Input

    9. VPP - Input Sailing Parameters: Headings, wind speeds and sea conditions Sail combinations e.g. mainsail & spinnaker

    10. VPP - Input

    11. VPP - Output

    12. VPP - Solver

    13. VPP - Solver Calculates: Steady state speed Vs and heel angle f For given: True wind speed VT and heading angle bT to the wind

    14. VPP Two Part Structure

    15. VPP Boat Model Aerodynamic: Determine apparent wind angle & speed sails encounter Predict aero lift & drag Resolve into thrust, sideforce, heeling moment Hydrodynamic: Predict resistance and righting moment Given that hydro sideforce equals known aero sideforce

    16. VPP Boat Model Internal force models e.g. DSYHS Experimental data: wind & tank data

    17. VPP Solution Algorithm Rigid body equilibrium. Yacht has 6 degrees of freedom, yet only 2 usually considered in VPP: longitudinal force rolling moment Vertical force & pitching moment assumed to be balanced by hydrostatics. Yawing moment assumed to be balanced by rudder angle. Sideforce balanced when yacht takes up leeway angle to develop hydro sideforce to balance aero sideforce.

    18. VPP Solution Algorithm

    19. VPP Solution Algorithm Therefore for a given bT, there are 4 equations with 4 unknowns. Newton-Raphson iterative solution used.

    20. VPP Output Polar Plot

    21. Race Modelling Performance prediction for N yachts as defined by V = f(Vt, Bt). Specification of M regattas, comprising races defined by joint probability density of wind speed and heading p(Vt, Bt), and weights W. Comparative analysis of N yachts for M regattas.

    22. Event Specification Course, e.g. windward-leeward, olympic, Sydney-Hobart, Round the World. Race, i.e. a course with wind speed information. Typically probability function of true wind speed (normal distribution with mean value and std deviation) Route, a race with joint distribution of true wind angles and true wind speeds. For given race or route, calculate elapsed time for expected distributions of wind speed and angle. Regatta or Series, a combination of races or routes.

    23. Analysis & Ranking For course: Deltas of relative performance in terms of seconds per mile as a function of true wind speed. For races: Expected elapsed time for each boat & compare differences. Boat with fastest time is the winner. For regattas: Probability and game theory methods.

    24. VPP - Exercise Formation Design System SPAN Use IMS sample yacht obtain polar plot Set up IACC yacht with rig obtain polar plot Change rig dimensions and look at change in polar plot output.

    25. Sum over one complete wave period all local damping waves generated by number of sections along yacht length. Sum over one complete wave period all local damping waves generated by number of sections along yacht length.

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