Velocity prediction program
- Velocity prediction program
A Velocity prediction program or VPP is a program which solves for the performance of a sailing yacht in various wind conditions by balancing hull and sail forces. VPPs are used by yacht designers, boat builders, model testers, sailors, sailmakers and America's Cup teams to predict the performance of a sailboat before it has been built or prior to major modifications.
Background
The first VPP was developed at MIT during the early 1970's when Commodore H Irving Pratt funded research to predict the performance "of a sailing yacht, given knowledge of its hull, rig and sailplan geometry."
Methodology
VPPs are iterative programs which require educated guesses of initial parameters to begin operating. Generally VPPs are composed of two mechanisms, a boat model and a solution algorithm. Initial guesses of parameters including boat speed (Vs), heel angle (Φ), number of reefs and sail flatness are input into the boat model. Using these input parameters the solution algorithm calculates the different between the propulsive force of the sails and the resistive force of the hull. It also calculates the righting moment created by the hull and the operational heel angle. Since the propulsive force and the resistive force are not likely to be equal on the first iteration, the solution algorithm has the responsibility of adjusting the input parameters and balancing the forces until it produces the maximum possible speed at each true wind angle.
Hydrodynamic force model The resistive forces acting on a hull and its appendages (keel, rudder and other fins) can be broken down into a number of smaller components.
#Viscous drag
#Residuary resistance
#Induced drag
#Heel induced drag
#Added resistance in waves (RAW)
Aerodynamic force model
Solving and optimization
Presentation
Uses
Commercial VPPs
WinDesign AHVPP Sailfish Yacht Analyzer
References
Claughton, Wellicome and Shenoi (1998). "Sailing Yacht Design: Theory." University of Southampton, 109-143. ISBN 0-85432-829-7.
See also
* International Rule
* Universal Rule
* International Offshore Rule
External links
* [http://ocw.mit.edu/NR/rdonlyres/Ocean-Engineering/13-734Fall2003/DE815951-BB6D-481E-957B-4F8A7B0249EB/0/ims_rule_book.pdf IMS Rule Book]
* [http://www.wumtia.soton.ac.uk/brochures/WindesignBrochure.pdf WinDesign VPP]
* [http://aerohydro.com/products/marine/ahvpp.htm AeroHydro VPP]
* [http://www.techsail.com/ Sailfish Yacht Analyzer]
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