Friday Morning
Investigation Of Scale Effects In Sailing Yacht Performance Prediction By Numerical And Experimental Methods, Mustafa Insel And Ziya Saydam
Substantial amount of research has been carried out in the past to enhance the testing techniques and to increase the accuracy associated with tank testing of sailing yachts. Majority of this work was associated with high budgeted campaigns; large models, long waiting times and high budgets became standard practice in the field. This led to lack of accessibility for low budgeted campaigns and for designers of ordinary sailing yachts to these tests.
A research study has been initiated to investigate the scale effects associated with tank testing of sailing yachts. The intention has been to make best use of modern experimental and computational methods to understand the scale effects in conjunction with systematic tank tests. Both viscous and wave components were considered for investigation of scale effects in sailing yacht performance prediction. Four different scale models ranging from 1/4 to 1/10 of a TP52 yacht have been tested in the towing tank in upright and heeled condition while full, half and quarter scale analysis have been carried out with a RANS code. The wave pattern measurements were conducted for all upright and heeled cases with the use of three wave probes on each side. Variation of drag, side-force, running attitude and wave pattern have been investigated
Least Squares Estimation of Sailing Yacht Dynamics from Full-Scale Sailing Data, Katrina Legursky
Sailing yachts have great potential to act as future long-term oceanic observing platforms, yet to date there have not been complete autonomous sailing systems robust enough to handle long term operation in the harsh ocean environment. The basis of control system design is a model capable of describing and capturing the necessary behavior of the system to be controlled. A common method employed in the aerospace industry when designing autonomous autopilots is parameter estimation where a physics-based model dependent upon motion variables, control inputs, and aerodynamic parameters is derived, then full-scale measurements are taken and used to estimate the aerodynamic parameters. This work presents preliminary results of least squares estimation (LSE) applied iteratively to fit a non-linear physics based sailing yacht model containing both aerodynamic and hydrodynamic parameters.
A physics-based model previously presented by the author is used as the basis for this estimation. The model is nonlinear in some of the parameters, thus a recursive estimation procedure is implemented.
LSE may be used for systems where the model structure is known except for a defining set of constant parameters that make the system unique. The method minimizes a cost function defined as the sum square difference between the measured output and the model predicted output. For non- linear systems, the method is applied iteratively with parameter estimates for the next step generated through the minimization of the cost function by the Levenburg-Marquardt method.
A Precision 23 sailboat, Avanti, has been outfitted with an adequate sensor system to do parameter estimation. The sensors provide boat speed through the water, apparent wind speed, wind angle, GPS position, velocity, heading, rudder angle, sail angle, Euler angles (roll/heel, pitch, and heading) and rates, and accelerations. Data is collected by a Labview Virtual Instrument (VI) PC interface which uniformly records and timestamps the data. Sailing tests are performed on Clinton Lake in Lawrence, KS. In addition steady state sailing, the data includes maneuvers designed to characterize the dynamic response of the vehicle to individual inputs, including rudder inputs, changes in sail angles, and responses to wind gust and wind shift. Tests have been done in different wind and sea states, effectively capturing the boat behavior in differing conditions. The data from the tests is used with an iterative LSE procedure to estimate parameters from the physics-based sailing yacht model.
Delft Systematic Yacht Hull Series Presentation, Lex Keuning
Friday Afternoon
Keelboat Yaw Gyradius Measurement, Peter Hinrichsen
Moment of Inertia measurements using a bifilar suspension normally entail accurate measurement of the length l and spacing 2d of the suspension, and of Ty the period of yaw oscillation. The latter requires that the motion is predominantly rotation about a vertical axis i.e. yaw, with negligible pitch or lateral sway, and so requires precise release of the hull. For an athwartships suspension the sway motion is that of a simple pendulum of period Ts. A modification which takes advantage of the sway to act as the clock, i.e. measuring the ratio Ty/Ts of the yaw and sway periods of oscillation is described.
This ratio is easily derived from the beat pattern of the motion of the bow or the stern, and can even be quite precisely estimated just by inspection. The yaw gyradius ky is then d, half the suspension spacing, times this ratio, i.e. ky = (Ty/Ts)d. This is a generalization of the previously suggested method in which the spacing d was adjusted to make Ty = Ts so that ky = d. It eliminates many calibration uncertainties so the precision is significantly improved and predominantly governed by the error ±δd in measurement of the suspension spacing.
A New Real-time Method for Sailboat Performance estimation based on Leeway Modeling, Ronan Douguet, Jean-Philippe Diguet, Johann Laurent, Yann Riou
This paper presents new methods for real time estimation of leeway and ocean stream, which are based on boat displacements. We propose two solutions that rely on several types of Kalman filters. The first one uses the empirically leeway definition and allows finding the key parameter of this formula. The solution works properly if the error of the formula of leeway remains limited. The second solution takes advantage of an additional sensor and we compare three methods to linearize boat displacements, which are based on a close-loop model including cascaded filters. These methods are tested on simulation and on real data collected with a maxi multihull. The results first validate the use of a DVL sensor for leeway estimation but also show that it requires the implementation of a complex and specific step of signal processing. Secondly our study demonstrates the relevancy of the close-loop approach and shows that a solution, based on UKF filters, provides a relevant method to cope with accuracy and stability in case of sensor data outage.
Mainsail Planform Optimization For IRC 52 Using Fluid Structure Interaction, Robert Ranzenbach, Dave Armitage and Adolfo Carrau
Most IRC 52 based upon existing TP52 retain the original rig proportions and mainsail girths to avoid the cost and disruption of a rig change and to not disturb the finely tuned yaw balance. It is not obvious whether the mainsail proportions essentially dictated by the TP52 box rule (aggressively square topped mainsails) are actually optimal under IRC even though IRC 52 with TP52 style mainsails tend to successfully compete under IRC. To determine the answer to this question, a planform investigation was performed as collaboration between Botin Partners and Quantum Sail Design Group.
The mainsail planform study utilized a Fluid Structure Interaction (FSI) program developed by QSDG known as IQ Technology (IQT) that consists of sail geometry definition, inviscid Computational Fluid Dynamics (CFD), Finite Element Analysis (FEA), and shape validation (based upon VSPAR) modules. The study also utilized the Botin Partners Velocity Prediction Program (VPP). Applicability of the inviscid CFD was validated by comparison to a limited number of viscous flow solutions, i.e. RANS analysis, performed by Porto Ricerca.
Two mainsails were considered, a conventional TP52 style and an alternative that was chosen to be closer to the IRC default girth values. To maintain sail area and yaw balance, the alternative mainsail had a longer P and E.
Results from the study suggest that a TP52 style mainsail is not optimal under IRC. The combination of rating reduction and predicted performance advantages over a wide range of wind speeds suggest that an alternative mainsail with larger P and E with girth values closer to the IRC default values is a superior choice for IRC 52.
An Experimental Validation Case For Fluid-Structure-Interaction Simulations Of Downwind Sails, H. Renzsch, K. Graf
In this paper the results of wind tunnel tests on two different asymmetric spinnakers are presented. During these tests forces and flying shapes at different apparent wind angles and trims were recorded by 6DoF balance and photogrammetry. As these tests are intended as a validation benchmark for FSI-simulations on downwind sails, the sail moulds, incident flow data as well as measured forces and flying shapes will be made publically available.
Saturday Morning
A Refinement of the Method Used to Determine the Balance of a Sailing Vessel During the Design Phase, with Application to Sail Design and Subsequent Sail Selection and Sailing Operations, Capt. Iver Franzen
The thrust of this paper is to attempt to define the relationship between the sail plan and the hull with somewhat more precision. Because of those factors that effect balance including and beyond those addressed by the traditional design approach as taught by most current texts on sailboat balance, the need for the factor "lead" will never go away. However, by including, as will be demonstrated, an additional balance factor, specifically the sheet lead positions, into the balance equations during the design phase, sailboat balance can be predicted with better accuracy. The primary objective of this refinement will be the ability to design sail profiles, especially the compliment of headsails, which will result in the least (adverse) change of balance when changing from one headsail to another, and which can be applied to either new designs, or to existing boats in need of out-of-balance remedies. This would mean that each anticipated sail combination can be analyzed for its lead, and therefore adjusted during the design phase to insure that proper helm is maintained from one combination to the next.
Uncertainties In The Wind-Heel Analysis For Traditional Sailing Vessels: The Challenges It Presents For Forensic Analysis Of Sailing Vessel Incidents,
Bruce Johnson, William Lasher, Matt Erdman, Jan Miles, and Bill Curry
There are many uncertainties in the interpretation of full scale sailing vessel data taken under dynamic conditions, and even more uncertainties when forensic analysis is attempted based only on survivor’s recollections. Frequently the analysis is based on static equilibrium assumptions, sometimes modified to steady state motions of the wind and heeling response of the vessel. Dynamic conditions are generally non-deterministic and statistical methods must be used. Even more complicated is the non-stationary random process nature of most accidents.
In the wind-heel research carried out on Pride II, the authors have learned that wave action frequently adds uncertainty in establishing the cause of the resulting heeling action. The best data is found in steady 10 to 20 knot wind strengths in minimum waves found in the lee of a shoreline. This criteria can be interpreted as minimizing the uncertainties in characterizing the wind-heel performance of a given sail combination at normal angles of heel.
Examples of quasi steady state response are presented in the paper as characterized by the Wind Heel Stiffness Ratio, (WHSR) equal to the square of the apparent wind velocity divided by the resulting heel angle. This WHSR for each sail combination is most easily established by a maneuver the crew of Pride II has deemed “The Crazy Ivan”. However it is uncertain whether this concept can make useful predictions at much higher angles of heel beyond that of GZmax in the absence of any good data taken during these conditions. CFD studies of various sail combinations give very good agreement between the recorded wind-heel response of the vessel and the CFD predictions and thus provide a method of predicting the normal wind heel response of a traditional sailing vessel during the design process.
The paper discusses operational guidance uncertainties that appear as a “fork in the road” decision with bearing away as one path and heading up as the other path. The paper examines the tradeoffs in the decision making process relative to the type of vessel involved and the observable wind and sea conditions at the time. Recent attempts to re-analyze the dismasting of Pride II in 2005 and the sinking of the S/V Concordia off Brazil in 2010 are also included.
The Evolution of Design: SALTS New Sail Training Schooner Project,
Stephen Duff, Fabio Fossati, Andy Claughton, Will Krzymowski, Tony Anderson
The Sail and Life Training Society is building a new purpose-designed 35m wooden sail- training schooner for unlimited international operations. Working with an international team of consultants, SALTS has initiated an ambitious agenda of analytical and experimental investig- ations to support design, including a parametric study of hull form as it relates to stability at high angles of heel, the development of bespoke parametric design and analysis tools using the graphical algorithm editor Grasshopper, a towing tank campaign at the Wolfson Unit to investigate the behavior of three keel profiles, and a wind tunnel campaign at Politecnico di Milano to investigate the behavior of fifteen sail-plans. Preliminary results from these studies will be presented, set in the context of the unfolding story of the evolution of the design of the new vessel.
Footy Presentation, Christer Broman
Saturday Afternoon
ORC Presentation,
Andy Claughton and Jason Ker
The International Technical Committee of the Offshore Racing Congress has in the last year completely revised one of the major components of the the VPP used for yacht handicapping.
This has been a complete change to the way Residuary resistance is calculated to both improve accuracy and to limit the opportunities for exploitation by over-zealous designers. It was accomplished by a re-analysis of the Delft Systematic Yacht Hull Series test data and a large tranche of complementary Computational Fluid Dynamics.
On The Hydrodynamics Of A Skiff At Different Crew Positions, Ignazio Maria Viola And Joshua Enlander
A set of towing tank tests was undertaken on a 1:4-model-scale high-performance small sailing boat, which was a candidate for the 2016 Olympic games. The resistance, sink and trim were measured and uncertainty analysis was completed. The boat was tested for different longitudinal positions of the crew in displacement, transition and fully planning regimes. The resistance measurements in the towing tank were well correlated with established empirical formulations developed for planning hulls. It was found that at low Froude numbers, forward crew positions allow lower resistance and resistance increases significantly for after crew positions, while at higher Froude numbers after positions allow lower resistance, and the resistance is less sensible to the crew position. These findings are in agreement with sailor experience and with measurements performed by other authors on large vessels.
A Measurement System for Performance Monitoring on Small Sailing Dinghies, Christoph Boehm, Robert Brehm, Janek Meyer,
Lars Duggen, Kai Graf
This paper describes a new performance monitoring system for dinghies and small sailing boats, developed in a collaborative project of the Yacht Research Unit Kiel (YRUK) and the Mads Clausen Institute (MCI) of the University of Southern Denmark. The system under development features a complete set of nautical instruments (wind, boat speed and heading, position) as well as dynamic sensors measuring the motion of the dinghy with additional audio and video streams for crew observations. Most sensors are integrated in a small lightweight housing also containing a main processing unit to be mounted on a dinghy. Some external miniaturized sensors (wind and water anemometers) are connected wirelessly. Data and media streams are recorded. Further a telemetry system allows online data transmission to a remote client operated on a coach boat. Analysis software allows the coach to visualize and analyze the performance of the dinghy. Both, the hardware system and the analysis software are presented here including first results from a field trial.
A Wind Tunnel Study Of The Interaction Between Two Sailing Yachts, P.J. Richards, D.J. Le Pelley, D. Jowett, J. Little, O. Detlefsen
The interference between two yachts sailing in several conditions is investigated in the wind tunnel by using two similar yacht models, one of which is mounted on a force balance and the other moved around the test section. The yachts were configured to sail close-hauled upwind at 20° apparent wind angle, downwind under asymmetric spinnaker at 60° and downwind under symmetric spinnaker at 120° apparent wind angle. The regions of positive and negative interference are determined through aerodynamic force measurement and flow disturbance measurement, and the sources of these effects investigated.
The Development of the New Volvo Class, Britton Ward, Chris Cochran and Farr Yacht Design, Ltd.
Although perhaps the most competitive Volvo Ocean Race in history, the 2012 event suffered from a lack of entries and a number of significant damage and breakage events that saw a number of boats fail to complete different legs. In response to this and the continued global economic challenges the Volvo Ocean Race organization made a dramatic shift in direction for the next two editions of the race opting to move to a smaller, less expensive yacht built to exceptionally strict one design standards. This has the effect of reducing costs for the boat, reducing crew sizes and dramatically reducing maintenance and repair and spares costs for the teams around the world allowing a very competitive campaign to be realized for under $15 million EUR.
The design brief for the NVC involves a significant number of challenges. It calls for a boat with a similar performance pedigree to the VO70 that it will replace, while requiring significantly enhanced structural margins for improved reliability, as well as reduced construction time, operating costs, and maintenance. This is a one design class that is competing at the pinnacle of the sport, so it needs to be built to an unprecedented level of construction accuracy and adhere to strict quality control requirements throughout the build process in order to be viewed as a successful one design by its users. All of this needs to be achieved in an unbelievably tight timetable in order to have at least 8 boats ready for the start of the next Volvo Ocean Race in late 2014.
This paper examines the some of the critical features of the design and how they compare to solutions on the previous VO70 yachts. A detailed review of the structural design is included to illustrate the efforts to improve construction efficiency, reduce cost and dramatically improve robustness of the yacht structures while minimizing the weight additions that result. Finally we review some of the extensive quality control procedures and manufacturing technology that has been employed in an effort to achieve a fleet of one designs that are as identical as possible