¨  Where a Vpp is in the design loop ¨  What a Vpp ultimately is and does ¨  Different approaches for different yachts and design phases ¨  Specifics of foiling yachts ¨  Dynamic Performance Prediction/Simulation

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Where a Vpp is in the design loop

VPP

Appendages Design • CFD • Laboratory Experiments • Full Scale Testing

Hull Design • CFD • Laboratory Experiments • Full Scale Testing

Sails Design • CFD • Laboratory Experiments • Full Scale Testing

Structures • CFD • Laboratory Experiments • Full Scale Testing

Systems • Simulators • Bench Tests • Full Scale Testing • Targets

Race Modeling •  Inputs

• Weather Models • Race Models • Straight Line Performance • Losses in maneuvers

• Outputs • Objective functions for Vpp • Yacth with best cnaches to

win regatta

GOAL of the design loop for a racing yacht: provide the crew with the yacht (or the yacths) that give them the best chances to win a regatta Factors that contribute to that: •  Straight line performance •  Maneuverability •  Reliability

Vpp helps with: •  Ranking different designs in terms

of straight line performance (eventally via race modeling)

•  Estimating sailing parameters to run CFD and experiments in the appropriate conditions

•  Estimating the static loads the yacht will see while sailing (in flat water and regular wind...)

•  Defining the ranges necessary for the trimming parameters to achieve the full straight line potential of the yacht

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What a Vpp ultimately is and does A Vpp is a constrained optimizer where: •  The objective function is related to the yacht’s straight line performance. For

example the Vpp can optimize: •  VMG at a certain Tws •  Boat Speed at a fixed Twa and Tws (also called VMM) •  Weighted averages of VMMs in a range of twa and Tws •  Time for a leg at one Tws taking into account losses for maneuvers •  As above, but including weighted averages for different Tws •  Differences against a rating system •  ....any other function of Tws and Twa

•  The constraints are: •  That the total forces and moments are in equlibrium at each calculated point •  That the input and outputs parameters are within the ranges allowed by the

models used for the hydrodynamic and aerodynamic forces and moments •  Any other constraint, for example:

•  That loads on certain parts of the yacth don’t exceed prescribed values •  That the equilibrium points found are within certain stability ranges

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What a Vpp ultimately is and does Inputs for the Vpp are: •  Aerodynamic and hydrodynamic forces and moments

•  CFD •  Laboratory experiments •  Full Scale experiments •  Analitical models •  Regressions on experimental data for similar yachts •  ....

•  Tws Outputs are •  Straight line performance (VMG, VMM, full speed polars accross the Twa, Tws

range) •  Boat attitudes (Twa, Speed, Sink, Trim, Heel, Leeway etc.) •  Trim parameters (Rudder angles, Sails trim etc.) •  Any output that the aerodynamicand hydrodynamic models are able to provide NB: if Inputs are inaccurate, the Vpp will provide inaccurate Outputs, but these will be very accurate...nevertheless useless! The secret of a good performance prediction is in the inputs so ultimately in the tools used to create those

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Different approchaes for different designs and design phases DESIGNS: Standard Monohull (fixed keel and one rudder, mainly full displacement sailing) •  Most of the time «4 DOF»: vertical force and pitch moment are typically constrained

outside the Vpp, when preparing the aero and hydro inputs (CFD/towing tank, wind tunnel etc.).

•  Sometimes 3 DOF, when impact of yaw moment equlibrium can be neglected. Fast Monohull (canting keel, daggerboards, planning while reaching and downwind) •  Ideally 6 DOF to be able to predict behavior while planning. •  This means CFD or experiments need to be run in such a way as to provide the

appropriate inputs.

Multi Hull •  Ideally 6 DOF, but can be ok with less (3 or 4) for cruising yachts. DESIGN PHASES: •  3 DOF is fine to get a first look at a new design, but is normally quikly repalced by

more DOF. •  Analytical or regression aero and hydro models are ok in early stages of a project.

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Specifics of foiling yachts •  4 DOF (Side Force, Vertical Force, Roll Moment, Thrust-Drag)

can be used in very early stages to get a feel of the basics, but 6 DOF becomes mandatory as pitch and yaw moments ar critical

•  Transition between «Non Foiling» and «Foiling Mode» is difficult to model properly as hydrodynamic forces change quite abruptely around that point. Needless to say that it is very important to get it right as in general performance gradients are steep there. Inputs need to be specific and accurate

•  Tws for foiling is closely related to foil size and foil size has in general negative impact on non foiling performance or high speed foiling performance. It is really important to target the proper Tws for foiling and the Vpp needs to be as reliable as possible in predicting it

•  Equilibrium on the foils is less stable (or even unstable for some of the DOF) than in displacement mode. Vpp needs to include specific outputs or constraints to allow only sailable solutions

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Specifics of foiling yachts •  Loads on the appendages are higher than for displacement

yachts. The Vpp needs to predict normal working loads for the systems and structure teams for them to properly execute their work. Hydro inputs need to allow the Vpp to correctly predict working loads

•  At high speed and high loads appendages start facing hydrodynamic phenomena as cavitation and ventilation. Ideally the Vpp inputs should include models for these phenomena in order to avoid over predicting performance

•  VPP can be used «off optimum» as a quasi-static simulator to help sailors analyze details of maneuvers on the foils

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Dynamic Performance Prediction/Simulation

Dynamic Performance Prediction and Simulation can help with any type of high performance yacth design precess, more so for foiling yacths to:

•  Analyze dynamic stability •  Analyze and improve sailing techniques (transitions, maneuvers...) •  Design control systems •  Anticipate boat’s behavior and avoid catastrofic accidents •  Provide dynamic loads •  Crew training off the water when time on the water is limited •  Improve race modeling and tactical softwares •  ...

To run proper simulations, hydro and aero models need to be appropriate and include dynamic effects. For the moment CFD cannot be used to provide those accurate models due to computing time, so models must be reasonably simplified. CFD, VPP and Simulation are still complementary and will continue to be until CFD will become quick enough to become «embedded» in the Vpp or Simulator. It is just a question of time.

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THE END