Yacht Design

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Yacht Design Technology

• Performance Evaluation

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Introduction

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

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Tools of the Trade

• Velocity Prediction Program (VPP)
• Race/Regatta/Event Modeller

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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

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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)

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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)

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VPP - Input
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VPP - Input
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VPP - Input

• Sailing Parameters
• Headings, wind speeds and sea conditions
• Sail combinations e.g. mainsail spinnaker

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VPP - Input
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VPP - Output
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VPP - Solver
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VPP - Solver

• Calculates
• Steady state speed Vs and heel angle f
• For given
• True wind speed VT and heading angle bT to the
  wind

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VPP Two Part Structure
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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

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VPP Boat Model

• Internal force models e.g. DSYHS
• Experimental data wind tank data

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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.

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VPP Solution Algorithm
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VPP Solution Algorithm

• Therefore for a given bT, there are 4 equations
  with 4 unknowns.
• Newton-Raphson iterative solution used.

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VPP OutputPolar Plot
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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.

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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.

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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.

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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.

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