Added Resistance in Seaways and its Impact on Yacht Performance

2007 ◽  
Author(s):  
Kai Graf ◽  
Marcus Pelz ◽  
Volker Bertram ◽  
H. Söding
Keyword(s):  
Strong Impact ◽  
Wave Spectra ◽  
Linear Extensions ◽  
Added Resistance ◽  
Optimum Length ◽  
Prediction Program ◽  
Strip Theory ◽  
Velocity Prediction ◽  
Added Resistance In Waves ◽  
Response Amplitude Operators

A method for the prediction of seakeeping behaviour of sailing yachts has been developed. It is based on linear strip theory with some non-linear extensions. The method is capable to take into account heeling and yawing yacht hulls, yacht appendages and sails. The yacht's response amplitude operators (RAO) and added resistance in waves can be predicted for harmonic waves as well as for natural wave spectra. The method is used to study added resistance in seaways for ACC-V5 yachts of varying beam. Results are used for further VPP investigations. The AVPP velocity prediction program is used to study optimum length to beam ratio of the yachts depending on wind velocity and upwind to downwind weighting. This investigation is carried out for flat water conditions as well as for two typical wave spectra. The results show that taking into account added resistance in seaways has a strong impact on predicted performance of the yacht.

scholarly journals VPP-Driven Sail and Foil Trim Optimization for the Olympic NACRA 17 Foiling Catamaran

2021 ◽  
Vol 5 (01) ◽  
pp. 61-81
Author(s):  
Kai Graf ◽  
Oliver Freiheit ◽  
Paul Schlockermann ◽  
Jan C. Mense
Keyword(s):  
Olympic Games ◽  
Strong Impact ◽  
Large Set ◽  
Prediction Program ◽  
Velocity Prediction ◽  
Rudder Angle ◽  
Boat Speed ◽  
The Olympic Games

Abstract. The Nacra-17 catamaran is currently the only type of multihull that participates in the Olympic Games. It features semi-L-shaped daggerboards, allowing the boat to foil. For maximizing boat speed, the sailors have to cope with a large set of trimming parameters. Boat speed depends on sail trim, but additional trim parameters also have a strong impact on boat speed: the rake of the daggerboard and the rudder, the platform trim and heel angle and the rudder angle. The project described here tries to assist the sailors in finding an optimized set of trim parameters. This is done with the help of a proprietary velocity prediction program, which - besides solving for equilibrium of all forces acting on the boat - searches for the set of daggerboard and rudder rake, rudder angle, heel angle and platform trim, for which performance yields a maximum. The paper describes the method as well as some of the results.

Developments in the IMS VPP Formulations

1999 ◽  
Author(s):  
Andrew Claughton
Keyword(s):  
Aerodynamic Force ◽  
Wind Tunnel Test ◽  
Force Model ◽  
Added Resistance ◽  
Detailed Model ◽  
Prediction Program ◽  
Construction Methods ◽  
Force Modeling ◽  
Velocity Prediction ◽  
Lift And Drag

The paper describes the improvements made to the aerodynamic and hydrodynamic force models of the Offshore Racing Council (ORC) International Measurement System (IMS) sailing yacht velocity prediction program (VPP) since 1990. The paper explains the mechanisms of the force modeling used in the IMS VPP to provide a framework within which the modifications and revisions to the VPP are described. The major revisions fall into three categories. 1) The hydrodynamic model, where a revised formulation for residuary resistance and characteristic length has been introduced, which includes modifications to both the residuary and viscous resistance components. Revisions to the drag due to heel and induced drag formulations are described that more accurately reflect the behavior observed from towing tank tests. 2) The added resistance in waves module was introduced to assist with the equitable handicapping of diverse bull types and construction methods, which affect the behavior of sailing yachts in waves. The mechanism by which the sea state is charaterised and the added resistance calculated is described. 3) The aerodynamic force model, which derives complete rig lift and drag coefficients from standard sail types is described. The behavior of the VPP force model is compared with wind tunnel test results, and the recent additions of coefficient sets for a range of different sail types is described. Finally the components of a more detailed model of hull and rig windage are outlined.

The Application of VPPs to Practical Sailing Problems

1987 ◽  
Author(s):  
Kart L. Kirkman
Keyword(s):  
Prediction Program ◽  
Widespread Acceptance ◽  
Velocity Prediction ◽  
Do So

The velocity prediction program, VPP, appeared on the yachting scene about ten years ago and it now dominates design and sailing. Originally implemented as a handicapping tool under the Measurement Handicap System, now accepted internationally as IMS, it has seen widespread acceptance for many other uses, from design to tuning and racing. This capability means that it is productive, even necessary, for the typical sailor interested in good performance to understand how to apply a VPP to his activities. To do so requires an appreciation of how a VPP functions and how it is applied to practical sailing problems, such as sail selection or tactics. The paper presents a review of VPP fundamentals and then treats the following applications: - Sail selection and strategy for offshore yachts. - Tuning and optimization of all boats. It is the goal of the paper to impart a working understand­ing of the VPP to many sailors so that they can take advantage of the technology in their normal activities.

The Effect of Pitch Gyradius on Added Resistance of Yacht Hulls

1991 ◽  
Author(s):  
James F. Moran
Keyword(s):  
Water Resistance ◽  
Wave Spectrum ◽  
Response Amplitude ◽  
Added Resistance ◽  
Regular Waves ◽  
Low Frequencies ◽  
Irregular Wave ◽  
Wave Data ◽  
The Difference ◽  
Response Amplitude Operators

The purpose of this investigation was to determine the effect of pitch gyradius on added resistance of yacht hulls. Tank testing of a model yacht in head seas was performed in the Webb Robinson Model Basin. The model was tested in regular waves at two speeds and five variations of gyradius. The model was also evaluated in irregular seas of the Pierson-Moskowitz spectrum at various speeds with two gyradii. Response Amplitude Operators were developed from the regular wave data and comparisons made. The irregular wave data were analyzed for the effect of speed on the difference in added resistance between the maximum and minimum gyradius settings. Several conclusions were arrived at after analyzing the data. The Response Amplitude Operaters shift as the gyradius changes. In regular waves, at low frequencies of encounter, a lower, gyradius resulted in less added frequencies of encounter in regular waves, this trend reverses itself and the higher gyradii result in reduced added resistance. However, at higher frequencies of encounter in regular waves, this trend reverses, reverses itself in reduced added resistance. The peaks of the RAO curves shift to higher frequencies at higher gyradii. It was also concluded that at the higher speed, Froude Number of 0.3, the added resistance was lower relative to the still-water resistance for each gyradius tested. The irregular wave testing revealed the effect of the lower frequencies dominating the irregular wave spectrum. The minimum gyradius, in irregular seas showed less added resistance than the maximum gyradius. In addition, the irregular wave testing verified, the reduction of added resistance, relative to still-water resistance, at increasing speeds for both the minimum and maximum gyradii.

scholarly journals Rowing VPP(Velocity Prediction Program)

2003 ◽  
Vol 2003 (194) ◽  
pp. 67-73
Author(s):  
Hiroshi Kobayashi ◽  
Takeshi Kinoshita
Keyword(s):  
Prediction Program ◽  
Velocity Prediction

scholarly journals High Froude Number Experimental Investigation of the 2 DOF Behavior of a Multihull Float in Head Waves

2021 ◽  
Vol 6 (01) ◽  
pp. 1-20
Author(s):  
Paul Kerdraon ◽  
Boris Horel ◽  
Patrick Bot ◽  
Adrien Letourneur ◽  
David David Le Touzé
Keyword(s):  
High Performance ◽  
Good Representation ◽  
Prediction Program ◽  
Modeling Approach ◽  
Head Waves ◽  
Wide Range ◽  
Dynamic Velocity ◽  
Velocity Prediction ◽  
High Froude Number ◽  
Stability Issues

Dynamic Velocity Prediction Programs are taking an increasingly prominent role in high performance yacht design, as they allow to deal with seakeeping abilities and stability issues. Their validation is however often neglected for lack of time and data. This paper presents an experimental campaign carried out in the towing tank of the Ecole Centrale de Nantes, France, to validate the hull modeling in use in a previously presented Dynamic Velocity Prediction Program. Even though with foils, hulls are less frequently immersed, a reliable hull modeling is necessary to properly simulate the critical transient phases such as touchdowns and takeoffs. The model is a multihull float with a waterline length of 2.5 m. Measurements were made in head waves in both captive and semi-captive conditions (free to heave and pitch), with the model towed at constant yaw and speed. To get as close as possible to real sailing conditions, experiments were made at both zero and non-zero leeway angles, sweeping a wide range of speed values, with Froude numbers up to 1.2. Both linear and nonlinear wave conditions were studied in order to test the limits of the modeling approach, with wave steepness reaching up to 7% in captive conditions and 3.5% in semi-captive ones. The paper presents the design and methodology of the experiments, as well as comparisons of measured loads and motions with simulations. Loads are shown to be consistent, with a good representation of the sustained non-linearities. Pitch and heave motions depict an encouraging correlation which confirms that the modeling approach is valid.

Scoring IMS Regattas - An Empirical Study of Alternative Methods

1995 ◽  
Author(s):  
John W. Cane
Keyword(s):  
Empirical Study ◽  
Measurement System ◽  
Alternative Methods ◽  
Prediction Program ◽  
Data Points ◽  
Velocity Prediction ◽  
International Measurement

The International Measurement System (IMS) uses a computerized velocity prediction program (VPP) to calculate the performance of a meas­ured hull and rig in winds from six to twenty knots, at any sailing angle. A regatta is scored by comparing a yacht's performance with pre­dictions of the VPP. The winner is the yacht whose performance, relative to its VPP predic­tions, is the best, compared to all other yachts in its class or division. This paper discusses different methods of malc­ing the comparison and accounting for various factors in the race such as wind shifts and cur­rent on the course. Decisions made by race man­agers and/or developers of scoring programs can significantly impact results. Illustrative examples show the effects that these decisions can have. In 1994 the number of data points available for use in scoring yachts in custom courses doubled. Alternative ways of using these data are illus­trated by application to a sample regatta.

Relative Performance of Conventional Versus Movable-Ballast Racing Yachts

2005 ◽  
Author(s):  
Frank DeBord ◽  
Harry Dunning
Keyword(s):  
Physical Model ◽  
Morning Glory ◽  
Cfd Analysis ◽  
Design Issues ◽  
Design Features ◽  
Prediction Program ◽  
The Past ◽  
Trade Offs ◽  
Physical Model Tests ◽  
Velocity Prediction

Over the past few years several advanced concepts have gained wider acceptance from owners of large racing yachts and organizers of major international events. Two of these concepts, water ballast and canting keels, were evaluated during the design of the maxZ86 yachts Pyewacket and Morning Glory. This paper presents the key design features of these large movable ballast racing yachts and compares their performance to conventional racing yachts of similar size. Comparisons include results of physical model tests, CFD analysis using a panel code, velocity prediction program modeling, and sailing data from the existing boats. These results are accompanied by physical explanations of the differences, and the special testing and analysis requirements for the movable-ballast configurations are detailed. Finally, some of the design issues unique to the movable-ballast concepts and design trade-offs are discussed.

Upwind Sail Performance Prediction for a VPP including “Flying Shape” Analysis

2009 ◽  
Author(s):  
Brian Maskew ◽  
Frank DeBord
Keyword(s):  
Grid Point ◽  
Flow Simulation ◽  
Lattice Method ◽  
Prediction Program ◽  
Aerodynamic Pressure ◽  
Dynamic Velocity ◽  
Velocity Prediction ◽  
Coupled Structures ◽  
And Performance ◽  
Ultimate Objective

A coupled aerodynamic/structures approach is presented for predicting the flying shape and performance of yacht sails in upwind conditions. The method is incorporated in a flow simulation computer program, and is part of an ultimate objective for a simultaneous aeroelastic/hydro analysis in a Dynamic Velocity Prediction Program (DVPP), that will include a 6DOF motion solver, and at some point could include calculations in waves. The time-stepping aerodynamic module uses an advanced vortex lattice method for the sails and a panel method with special base separation treatment to represent the abovewater part of the hull and mast. A coupled inverse boundary layer analysis is applied on all surfaces including both sides of each sail membrane; this computes the skinfriction drag and the source displacement effects of the boundary layers and wakes, including bubble and leeside “trailing-edge” type separations. . At each step, the computed aerodynamic pressure and skin-friction loads are transferred to a coupled structures module that uses a network grid of tension “cords” in each sail membrane, each cord representing a collection of fiber “strings”. The solution of a structural equilibrium matrix provides the displacements needed to achieve balance between the aerodynamic and tension loads at each grid point as the shape iterations proceed. Details of the methodology used are presented and comparisons of predicted aerodynamic forces to wind tunnel results and an existing VPP sail model are provided. In addition, predictions are compared to some simple experiments to demonstrate the aerodynamic/structural coupling necessary to predict flying shape. Finally, an outline is given for incorporation of this methodology into the planned Dynamic Velocity Prediction Program.

Tacking in the Wind Tunnel

2009 ◽  
Author(s):  
Frederik C. Gerhardt ◽  
David Le Pelley ◽  
Richard G. J. Flay ◽  
Peter Richards
Keyword(s):  
Wind Tunnel ◽  
Aerodynamic Force ◽  
Three Dimensional ◽  
Added Mass ◽  
Mass Moment ◽  
Strip Theory ◽  
Dynamic Velocity ◽  
Order Of Magnitude ◽  
Velocity Prediction ◽  
Unsteady Effects

In recent years a number of Dynamic Velocity Prediction Programs (DVPPs), which allow studying the behaviour of a yacht while tacking, have been developed. The aerodynamic models used in DVPPs usually suffer from a lack of available data on the behaviour of the sail forces at very low apparent wind angles where the sails are flogging. In this paper measured aerodynamic force and moment coefficients for apparent wind angles between 0° and 30° are presented. Tests were carried out in the University of Auckland’s Twisted Flow Wind Tunnel in a quasi-steady manner for stepwise changes of the apparent wind angle. Test results for different tacking scenarios (genoa flogging or backed) are presented and discussed and it is found that a backed headsail does not necessarily produce more drag than a flogging headsail but increases the beneficial yawing moment significantly. The quasisteady approach used in the wind tunnel tests does not account for unsteady effects like the aerodynamic inertia in roll due to the “added mass” of the sails. In the second part of paper the added mass moment of inertia of a mainsail is estimated by “strip theory” and found to be significant. Using expressions from the literature the order of magnitude of three-dimensional effects neglected in strip theory is then assessed. To further quantify the added inertia experiments with a mainsail model were carried out. Results from those tests are presented at the end of the paper and indicate that the added inertia is about 76 % of what strip theory predicts.

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