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Journal ArticleDOI

Performance prediction for sailing dinghies

15 May 2017-Ocean Engineering (Elsevier)-Vol. 136, pp 67-79
TL;DR: In this paper, the effect of crew weight on sailing performance was studied by comparing time deltas for crews of different physique relative to a baseline 80kg sailor. But the results showed a relatively high sensitivity of the performance around a race course to the weight of the crew, with a 10kg change contr ibuting to timedeltas of more than 60 seconds relative to the baseline sailor over a race of one hour duration at the extremes of the wind speed range examined.
About: This article is published in Ocean Engineering.The article was published on 2017-05-15 and is currently open access. It has received 16 citations till now. The article focuses on the topics: Crew & Water transport.

Summary (4 min read)

3.1 Introduction

  • This model may be modified (as it is here) to take advantage of measured data where available.
  • The hulls tested in the development of the model were all round-bilge sailing yacht forms with principal parameters reflecting yacht design practice during the many years of testing.
  • Hence where hulls have principal form parameters falling outside the range of hulls tested in the generation of the Delft data set, the results may not be reliable.
  • Day & Nixon (2014) investigated the resistance of a Laser dinghy, using a hull model measured using an optical measurement system.

3.2 Hydrodynamic resistance

  • For the current purposes, therefore, the data from the model tests was used directly to predict the upright resistance of a Laser in the developed VPP by interpolation (and in some cases extrapolation) for weight and speed.
  • Since model tests were only conducted in the upright condition without appendages, and hence results were not available for other components of resistance.
  • The Delft framework considers eight components of hydrodynamic resistance: frictional and residuary resistance for the upright hull, viscous and residuary resistance for the keel in the upright condition, change in frictional and residuary resistance of the hull due to heel, change in residuary resistance of the keel due to heel, and induced drag of the hull/keel combination.
  • The change in frictional resistance with heel angle is assumed to relate only to the change in wetted area; this may be estimated from the curve of wetted area against heel angle, calculated using the CAD model generated.
  • The induced resistance is discussed further in section 3.4.

3.3 Hydrodynamic side force and yaw moment

  • The model as described above provides the information required for the VPP to satisfy equilibrium in the horizontal plane and also in heel.
  • Following Keuning and Verwerft, the lift component for the daggerboard is found as: (11) .
  • The total lift of the daggerboard and rudder for a given leeway angle and rudder angle is thus obtained from the sum of the two components given in equations (11) and (12).
  • The hydrodynamic yaw moment from the daggerboard and rudder can be easily calculated from the moments generated by the respective lift components.
  • The resulting moment thus depends both on the displacement and the heel angle.

3.4 Induced Resistance

  • The coefficients in this equation are tabulated for different heel angles.
  • The planform efficiency e for a tapered swept foil where .
  • Here the aspect ratio includes the image in the free surface.
  • The delta in the lift caused by the rudder angle is subtracted from the heeling force before applying equation (15) to estimate the hull and keel induced drag, and the delta in the rudder induced drag is then added to the total resistance.
  • Hence it can be seen that the majority of the resistance results from components either measured in the tank or those which can reasonably be assumed to be accurately calculated.

4 Stability of a sailing dinghy

  • The hydrostatic stability of sailing dinghies is strongly dependent on the crew position, since the crew typically contributes more than 50% of the total weight.
  • In this study the more conservative figure of 55% is adopted.
  • However the body position adopted by even the fittest athletes will be less straight than in the standing position due to the geometry of the side decks of the boat; hence the upper limit of righting moment will occur with a transverse offset of crew CG less than 55% of the crew height.
  • In some dinghies, the crew may be offset transversely due to the location of the toe strap; in trapezing dinghies, the crews’ feet could be located on the deck edge or racks.
  • Since the measurement was executed outdoors, the sail was not rigged in order to avoid unwanted effects due to wind.

5 Solution procedure

  • The approach outlined in the previous sections was implemented in an Excel Spreadsheet.
  • Based on input values of true wind speed and direction, boat speed, heel, leeway and rudder angles, the spreadsheet computed the aerodynamic drive and heeling force, the aerodynamic heeling moment and yawing moment, the maximum righting moment, and the hydrodynamic drag, side force and yawing moment.
  • The Excel “solver” was then used to solve the problem to maximise VMG both upwind and downwind.
  • The daggerboard was assumed to be fully down whilst sailing upwind and 50% down when sailing downwind.
  • The only exception to the constraints described above are for the case in which yaw balance was neglected in which the third and fourth constraints were not imposed, and transverse equilibrium was imposed implicitly by equating the hydrodynamic heeling force to the corresponding aerodynamic force in the calculation of hydrodynamic induced drag.

6.1 Validation and comparison with measured data and previous VPP studies

  • The results of the VPP may be validated by comparing with full-scale measurements.
  • The data set was extracted from the plots shown and is re-plotted here in Figure 3.
  • It appears that no attempt was made to discriminate between data gathered from steady-state sailing and that gathered during manoeuvres, hence it can be expected that some of the variations in speed with true wind angle may be caused by boat/sailor dynamics during manoeuvres (such as roll tacking and gybing).
  • A Laser can be expected to achieve maximum VMG upwind in true wind angles in the region around 40-46 degrees in flat water.
  • VPP results are plotted for 9.0, 9.5 and 10.0 knots; it can be seen that the boat speed is relatively insensitive to the wind speed over the range of angles up to about 50 degrees, which implies that the accuracy of the wind speed measurement is not critical at these headings.

6.2 Results for baseline crew

  • The overall VMG is calculated over a range of wind speeds by assuming a windward-leeward course with upwind and downwind legs of the same length.
  • The times for each leg are calculated from the individual VMG values and added to give total lap time; the overall VMG is then simply the total lap length divided by total lap time.
  • Here the deltas due to frictional and residuary resistance are plotted against wind speed along with the heel angle.
  • The apparent wind angle varies between around 27 degrees in 5 knots of wind up to around 33 degrees in 15 knots; all relatively close to the angle for which the sail generates maximum lift coefficient.
  • It can be seen that upright hull resistance is dominant downwind, and less so upwind, for which induced drag becomes increasingly important as wind speed increases.

6.3 Yaw Balance

  • In order to examine the impact on the prediction of the boat performance of the inclusion of yaw balance, the runs described above were repeated without imposing yaw moment equilibrium; hence the boat was assumed to track in a straight line with the rudder central.
  • The results in terms of boat speed are shown in Figure 13.
  • It can be seen that including the yaw balance results in an increase in predicted upwind speed averaging around 1.0%.
  • Since the rudder is typically more efficient than the hull/keel combination this leads to a reduction in induced drag and increased speed.
  • From an aero-hydrodynamic perspective, a reason often quoted for heeling to windward downwind is to move the centre of aerodynamic pressure of the sail over the hull, thus reducing yawing moment and in turn minimising the need to use the rudder to maintain track.

6.4 Impact of Sailor Physique

  • At that point the 90kg crew becomes fastest upwind.
  • It is often quoted (e.g. Goodison (2008)) that the ideal crew weight for a Laser is around 80kg; interestingly there is only a small region (9.4-10.2 knots) for which 80kg is the fastest weight, and the benefit is presumably gained through retaining competitiveness over a wide range of wind speeds.
  • In the light wind region the effect of crew height is small, with only a very small penalty for taller crews due to increased aerodynamic drag; the penalty for additional 10 kg weight is around 40s in an hour, with a similar benefit for a reduction of 10kg in weight.

7 Conclusions

  • The key issues for performance prediction for sailing dinghies have been addressed, and illustrated through the development of a customised VPP for the Olympic Laser class dinghy.
  • The hydrodynamic model utilises tank test data along with standard Delft series results to predict the resistance.
  • The VPP allows identification of the relative importance of different hydrodynamic and aerodynamic drag components, in particular the importance of aerodynamic drag of the hull and crew on the boat performance in upwind sailing.
  • Finally, it would be of interest to gather more measured data, using more modern technology to allow more confident validation particularly for downwind sailing.
  • Heel influence coefficient ysc Local section area coefficient DC Drag coefficient * DC Depowered drag coefficient DpC Parasitic drag coefficient DsC Separation drag coefficient DvC Viscous drag coefficient LC Lift coefficient * LC depowered lift coefficient maxLC Maximum lift coefficient .L kC Lift coefficient of keel .L rC Lift coefficient of rudder mC Midships section coefficient pC Prismatic coefficient twistC.

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Citations
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Journal ArticleDOI
TL;DR: In this paper, the structural response of an eco-sustainable sailing yacht to different loading conditions, typical of those acting during regattas, was investigated using finite element method (FEM) tools.
Abstract: The use of finite element method (FEM) tools is proposed to investigate the structural response of an eco-sustainable sailing yacht to different loading conditions, typical of those acting during regattas. The boat is, in particular, a 4.60 m dinghy with the hull and the deck made of an hybrid flax–cork sandwich and internal reinforcements made of marine plywood. A preliminary activity has consisted in the refitting of an existing model in order to reduce the hull weight and to improve performances during manoeuvrings. These tasks have been interactively simulated in the virtual environment of the boat CAD model, where longitudinal and transversal reinforcements were enlightened and the maximum beam reduced. At the same time, results of FEM simulations on the modified model were analysed in order to verify the structural integrity. Shape modifications have been applied to the real model in laboratory and the resulting hull has been instrumented with strain gauges and tested under rigging conditions to validate the numerical procedure. Finally, the FEM model was used to predict the response of the boat to loading systems typical of sailing conditions.

11 citations

Journal ArticleDOI
TL;DR: Performance in the Laser class will be determined by the tactics and morphological characteristics of the sailor (height and sitting height), and the variables that are most related to performance are age and sailing experience.
Abstract: Despite the relationship between performance and anthropometric characteristics, strength, and endurance in the action of dinghy hiking, there is no equation to predict the position obtained in competition. The purpose of this study was to examine the effects of anthropometric characteristics, strength, and endurance on the performance of the sailor. Twenty-nine male sailors of the Laser class were evaluated according to age, navigation experience, strength and resistance tests in a simulator, body weight, size, sitting height, Body Mass Index (BMI), body fat percentage, trochanteric length, thigh length, tibial length, foot length, abdominal perimeter, and upper thigh perimeter. The results show that the variables were related to performance are age, navigation experience, height, and length of the thigh. The variables that are most related to performance are age and sailing experience. Seventy-six percent of the performance can be estimated using the following equation: 311.971 + (−1.089 × height) + (−1946 × age) + (−1.537 × thigh length). Performance in the Laser class will be determined by the tactics (age and sailing experience) and the morphological characteristics of the sailor (height and sitting height).

9 citations


Cites background from "Performance prediction for sailing ..."

  • ...The main objective of this maneuver is to maintain stability, which allows the sailor to use the force of the wind to increase the speed of the boat to its maximum during most of the route [3]....

    [...]

Journal ArticleDOI
15 Jan 2021-Sensors
TL;DR: Performance seems to be more strongly influenced by technical variables, such as speed, than by tactical variables, because the highest-level sailors presented a higher speed in upwind/downwind/beam reach and a shorter time inupwind and beam reach.
Abstract: Formula Kite is an Olympic sport that mainly differs from other kitesurfing modalities for the use of a hydrofoil. It is considered an extreme sport due to the great technical ability required. Regarding performance, the variables that determine performance in a real competition situation have not been studied, and even less so with Olympic sailors. Therefore, the objective of this study was to determine the technical and tactical variables that differentiate elite sailors. The sample consisted of 42 Olympic sailors of the Formula Kite class, who were evaluated in three World Cups. Using a GPS device, the speed, distance traveled, maneuvers, and time spent on the courses of upwind, downwind, and beam reach were recorded. The highest-level sailors presented a higher speed in upwind/downwind/beam reach and a shorter time in upwind and beam reach. Performance seems to be more strongly influenced by technical variables, such as speed, than by tactical variables.

6 citations


Cites background from "Performance prediction for sailing ..."

  • ...The technical level of the sailor in the different courses carried out in a regatta will determine the speed of the board, and the VMG in the windward and leeward courses is considered the most important variable to evaluate the performance of the sailor [31,32]....

    [...]

  • ...Although the literature shows the relationship between performance and technical (velocity) and tactical (distance and maneuvers) in Windsurfing [27,30] and Laser [31,32] classes, to our knowledge, no study has provided the variables that determine performance in the Formula Kite....

    [...]

Journal ArticleDOI
TL;DR: The VMG is decisive in the performance of elite female sailors in the upwind, downwind, and broad reach courses, while in elite male sailors, performance is mainly influenced by speed in upwind and downwind and the distance covered in up wind.
Abstract: Laser class is an Olympic sport in which technical and tactical variables are very important in the performance of the sailor. However, the variables that determine performance in a regatta have not been studied, and less so with Olympic sailors. Therefore, the main objectives of this study are to analyze the technical and tactical variables that differentiate sailors based on their level of performance and sex and determine the most important courses in a regatta. The sample consists of 159 Olympic sailors (67 females) of the Laser class, who participated in a World Cup. Velocity made good (VMG), distance, and maneuvers were evaluated using Global Navigation Satellite System (GNSS) devices in the upwind, downwind, and broad reach courses. VMG in upwind and downwind is the technical variable that determines performance in the Laser class. The VMG is decisive in the performance of elite female sailors in the upwind, downwind, and broad reach courses, while in elite male sailors, performance is mainly influenced by speed in upwind and downwind and the distance covered in upwind. The maneuvers do not determine sailing performance in any of the courses of a regatta.

6 citations


Cites background from "Performance prediction for sailing ..."

  • ...The sailor’s technique determines the velocity of the boat, and the VMG on the windward and leeward courses is considered the most important variable in a regatta, since the courses of a dinghy sailing are relatively simple and well defined, and, in many windward-leeward courses, two legs are navigated, one windward (upwind) and the other one leeward (broad reach and downwind) [10,11]....

    [...]

01 Jan 2019
TL;DR: This study analyzes how the wind determines the optimal time-path of Lasers, one of the smallest sailboats that compete during the summer Olympic Games, and proposes to model the sailboat in 3-dimensions including the X-coordinate of the sail-man position.
Abstract: Sailing against the wind follows a zig-zag trajectory. To find the optimal time and path-trajectory to move from one target to another during a race, this study analyzes how the wind determines the optimal time-path of Lasers, one of the smallest sailboats that compete during the summer Olympic Games. To answer this question, this study uses four wind models in an algorithm developed in MATLAB to find the optimal time-path. The wind models were forecasts and wind measurements for the area of race R1 from the World Cup Series 2018 at Hyeres, France. One of the wind models used were a Weather Research and Forecasting model (WRF) with a grid resolution of 1km, a time step of 10 minutes. On the other hand, the most basic model was a constant and uniform wind field. The race R1 has three lines, limited by two buoys, and one point(buoy), one line and one point define a leg. R1 has five legs and two of them are against the wind. The results, time and path-trajectories, of each of the wind models, were compared with the results of the top 10 winners of the race. They showed that the legs sailed against the wind are also characterized by the location of the sailboats on the start line. The times of these legs using the WRF wind model and the race-time had an error of less than 5%. For the prediction of the start location, it was the same as the winner of the race. However, the direction of the paths was not predicted accurately for these legs. Using the constant and uniform wind scenario, the percentage error of the race-time respect to the winner is about 7%. However, the direction of leg 2 is not even similar to the winner. To review the effects of the heights of the waves this study proposes to model the sailboat in 3-dimensions including the X-coordinate of the sail-man position. In addition, a 3D model allows the analysis of how the center of effort (CE) on the sail is affected by the current and waves.

4 citations


Cites background or methods from "Performance prediction for sailing ..."

  • ...Since for Olympics Sailing Races, it could represent more than 50% of the total mass of the sailboat (m)[18]....

    [...]

  • ...5, the values taken were the smallest with a reduction of the area of 20 % to consider shielding from the cockpit [18]....

    [...]

  • ...5b) The literature regarding VPP for laser boat classes is limited and it is mainly accounted in [18], the comparisons made here are only valid for wind speed between 4 and 16 knots, while races are performed up to 25 knots....

    [...]

  • ...005 and ARE is based on the rig geometry and calculated according to it [18]....

    [...]

  • ...These coefficients model the behavior of the sails and the athlete under strong wind conditions and it includes not only the upwind conditions but also the downwind course [18]....

    [...]

References
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01 Jan 1987
TL;DR: In this paper, the author's theories on the design and handling of sailing craft and a follow-up to his "Sailing Theory and Practice" are presented. But the authors do not discuss the performance and efficiency of aerofoils and hydrofoils, the principles underlying high speed sailing and recent developments in keel shapes.
Abstract: Incorporating many years of research, this book contains the author's theories on the design and handling of sailing craft and is a follow-up to his "Sailing Theory and Practice". Clear explanations and calculations help to quantify the many factors which determine a sailboat's performance. This edition incorporates new research on hull and sail behaviour, the performance and efficiency of aerofoils and hydrofoils, the principles underlying high speed sailing and recent developments in keel shapes, with particular reference to 12 metre yacht designs. The author Professor Tony Marchaj, is a former Polish Finn champion and is now an independent aerodynamic and research scientist.

134 citations

Journal ArticleDOI
TL;DR: The results were better than those of other researchers who did not assess aerodynamic drag during effort at race pace and who employed different wheels and the validity, reliability, and sensitivity of the wind tunnel and aerodynamic field testing were addressed.
Abstract: The aims of this study were to measure the aerodynamic drag in professional cyclists, to obtain aerodynamic drag reference values in static and effort positions, to improve the cyclists' aerodynamic drag by modifying their position and cycle equipment, and to evaluate the advantages and disadvantages of these modifications. The study was performed in a wind tunnel with five professional cyclists. Four positions were assessed with a time-trial bike and one position with a standard racing bike. In all positions, aerodynamic drag and kinematic variables were recorded. The drag area for the time-trial bike was 31% higher in the effort than static position, and lower than for the standard racing bike. Changes in the cyclists' position decreased the aerodynamic drag by 14%. The aero-helmet was not favourable for all cyclists. The reliability of aerodynamic drag measures in the wind tunnel was high (r > 0.96, coefficient of variation < 2%). In conclusion, we measured and improved the aerodynamic drag in professional cyclists. Our results were better than those of other researchers who did not assess aerodynamic drag during effort at race pace and who employed different wheels. The efficiency of the aero-helmet, and the validity, reliability, and sensitivity of the wind tunnel and aerodynamic field testing were addressed.

119 citations

Frequently Asked Questions (1)
Q1. What are the contributions in this paper?

This study describes the development of an approach for performance prediction for a sailing dinghy. The effect of crew weight is studied by comparing time deltas for crews of different physique relative to a baseline 80kg sailor. Results show relatively high sensitivity of the performance around a race course to the weight of the crew, with a 10kg change contributing to time deltas of more than 60 seconds relative to the baseline sailor over a race of one hour duration at the extremes of the wind speed range examined.