THE WORK ACHIEVED WITH THE AIL DYNAMOMETER BOAT FUJIN, AND THE ROLE OF FULL CALE TET A THE BRIDGE BETWEEN MODEL TET AND CFD Y. Masuyama, Kanazawa Institute of Technology, Japan, masuyama@neptune.kanazawa-it.ac.jp The work achieved with the sail dynamometer boat Fujin was reported. At first, the sail shapes and performance for upwind conditions were measured in steady sailing conditions. The results were compared with the numerical calculations. The database of three-dimensional coordinates of the sail shapes was also tabulated with the aerodynamic coefficients. The sail shape database provides a good benchmark for the validation of sail CFD in full scale level. Then, the aerodynamic force variation during tacking maneuvers was measured by Fujin, and a new simulation model of tacking maneuver was proposed. The simulated results showed good agreement with the measured data. Finally, the scale effect problem of wind tunnel tests was discussed. Wind Tunnel tests using model sails are performed at the region of critical Reynolds number. Therefore, the wind tunnel test had to be performed very carefully. On the other hand, the full scale tests using a sail dynamometer boat are free from scale effect problems and appear more promising. NOMENCLATURE C L, C D Lift force and drag force coefficients (-) C X, C Y Thrust force and side force coefficients (-) A ail area (m ) U A Apparent wind speed (AW) (m.s -1 ) V B Boat velocity (m.s -1 ) X, Y Force components along x and y-axis (N) K, N Moments around x and z-axis (N.m) γ A apparent wind angle (AWA) (deg) ρ Density of water (kg.m -3 ) ρ a Density of air (kg.m -3 ) Heel angle or roll angle (deg) Heading angle (deg) 1 INTRODUCTION Because the recent advances in computational fluid dynamics (CFD) further motivate the application of numerical simulations to predict the sail performance, there is an ever increased need for reliable experimental data for validation. Wind tunnel tests can be performed relatively easily, but scale effects related both to flow and structural aspects, which yield inaccuracy in sail shape measurements, are always present. Full scale onboard measurements are free from scale effect problems and appear more promising, but the challenge becomes how to accurately measure the forces acting on the sail. uch studies on sail force measurements were performed by Milgram et al., Masuyama et al. and Hochkirch et al., who built full-scale boats with onboard sail dynamometer systems. Milgram [1] showed in his pioneering work that the sail dynamometer boat, Amphetrete, is quite capable. This measurement system consists of a 35-foot boat with an internal frame connected to the hull by six load cells, which were configured to measure all forces and moments acting on the sails. In his work, the sail shapes were also measured and used for CFD analyses; unfortunately, details of the sail shape and performance data were not presented. Hochkirch et al. [] also built a 33-foot dynamometer boat DYNA. The aerodynamic forces acting on the sail were measured and compared with the results from wind tunnel tests [3]. The measured data were also used as input to the CFD calculation and a parametric survey was carried out [4]. However this work does not provide a database for the relation between sail shape and performance. Masuyama and Fukasawa [5, 6] were encouraged by Milgram s work, and built a sail dynamometer boat, Fujin. The Fujin is a 34-foot sailing cruiser, in which load cells, CCD cameras and sailing condition measurement system are installed to obtain the sail forces and shapes, and the boat attitude, simultaneously. In this report, the work achieved with the sail dynamometer boat Fujin is presented, and the role of full scale tests in the validation of CFD in full scale level is discussed. AIL DYNAMOMETER BOAT FUJIN.1 GENERAL ARRANGEMENT The Fujin was built in 1994. Fujin is a 1.3m-long ocean cruiser with a sail dynamometer system in the hull. Table 1 shows the principal dimensions of the boat and Figure 1 shows the sail plan of the Fujin. The sail dynamometer system is composed of a rigid aluminum frame and four load cells. The frame is separated structurally from the hull and connected to it by the load cells. The general arrangement of the dynamometer frame is given in Figure (a). The load cells are numbered in the figure. Two of these are 1-component load cells and the others are -component ones. The directions in which the loads were measured for each of
Table 1 Principal dimensions of Fujin HULL LOA LWL BMAX BWL Disp AIL I J P E [ton] 1.35 8.8 3.37.64 3.86 11. 3.61 1.55 4.51 (a) (b) Figure 1 chematic showing the sail plan of Fujin Figure General arrangement of dynamometer frame and directions of measuring components of each load cell the load cells are shown in Figure (b). Hence, these load cells form a 6-component dynamometer system, and their outputs can be transformed to the forces and moments about the boat axes using a calibration matrix. All rig components such as the mast, chain plates, winches, lead blocks, etc. are attached to the aluminum frame through the deck holes.. MEAUREMENT YTEM Figure 3 ea trial condition in light wind with 13% jib The sail shape was recorded using pairs of CCD cameras. The lower part of the mainsail was photographed using the CCD camera pair designated A in Figure 3. These were located at the mast top, 5 cm transversely from each side of the mast. The upper part of the mainsail was photographed using a portable video camera from below the boom. The lower part of the jib was photographed
using the camera pair designated B in Figure 3, which were located at the intersection point of the forestay and the mast, 1 cm transversely from each side of the mast. The upper part of the jib was photographed using a portable video camera from inside the bow hatch. The original data acquisition system consisted of a single PC which gathered all the data. However, the system was renewed later as a distributed system using three singlechip computers (Hitachi H8-636) connected with the Control Area Network (CAN) bus. The CAN is a highspeed, serial bus developed for the automotive environment and has a high level of noise immunity. 3 TEADY AIL PERFORMANCE FOR UP CONDITION 3.1 TET CONDITION AND ERROR ANALYI At first, the sail shapes and performance for upwind conditions were measured using mainsail and 13% jib in steady sailing conditions[6, 7]. Close-hauled tests were conducted over an apparent wind angle (AWA) range of to 4 degrees, and an apparent wind speed (AW) range of 5 to 11m/s. The effect of the AWA, and the draft and twist of the mainsail on the sail performance were measured. Data sampling was started when the sailing condition was considered to be in steady state. The sampling rate for the data acquisition system was set at 1Hz. Data sampling was continued for 9 seconds, and during this time the sail shapes were recorded using the CCD cameras. The boat was steered carefully during this time. However it was difficult to keep the variation in the AWA sufficiently small during the whole of the 9 seconds period. Therefore the steady state values for the aerodynamic coefficients were obtained by averaging the data over a 3 to 6 seconds period, in which the AWA was closer to the target value than during the whole 9 second period. For these tests if the range of deviation of AWA exceeded ±5 degrees, the results were discarded. All of the measured coefficients are plotted with error bars indicating the range of deviation over the averaging period. 3. NUMERICAL CALCULATION METHOD Numerical flow simulations were performed for the measured sail shapes and conditions. Two numerical methods were used: a vortex lattice method (VLM) and a Reynolds-Averaged Navier-tokes (RAN)-based CFD method. A vortex lattice method using a step-by-step procedure developed by Fukasawa [8] was employed to compare with the results of a RAN-based CFD calculation. The code of the RAN-based CFD method was FLOWPACK developed by Tahara [9, 1]. The method has an automatic gridding scheme, and complete multiblock domain decomposition feature. 3.3 AIL PERFORMANCE VARIATION WITH APPARENT ANGLE Figure 4 shows the performance variation for the mainsail and 13% jib configuration as a function of AWA. Figures 4(a) and (b) show the variation of lift and drag force coefficients C L,C D, and thrust and side force coefficients C X, C Y, respectively. In the figure the solid symbols indicate the experimental results and the open symbols indicate the calculated results using the VLM and the RAN-based CFD. For the experimental results, both data from the starboard (tbd) and port tack are shown. All of the measured coefficients are plotted with error bars indicating the range of deviation over the averaging period. There are some discrepancies between the data from each tack. During the experiments, efforts were made to remove this asymmetrical performance. However, the boat speed actually differed on each tack. It can be concluded that there was a slight asymmetry in the combination of the hull, keel, rudder and dynamometer frame. In this figure, AWA ranges from.3 degrees to 37.9 degrees for the port tack. The former is the closest angle to the wind that was achieved, and the latter is typical of a close reaching condition, where the sail is trimmed in the power down mode. There is some scatter in the experimental data because this is made up from measurements taken with the sails trimmed in slightly different ways. The experimental value of C L in Figure 4(a) varies with AWA from.91 to 1.58. For the close reaching condition, unfortunately, the sails were not well trimmed to satisfy the power down mode. The calculated results for C L using the VLM show good agreement with the experiments at AWA angles less than about 35 degrees. Over about 35 degrees, the calculated results are lower than the measured ones. This shows that the calculated results strongly indicate the effect of incorrect sail trimming. The results for C L using the RAN-based CFD show the same trends with the experiments, but are slight higher than those from the experiments for AWA between degrees to 3 degrees and lower for AWA greater than 3 degrees. In particular, the decrease in C L for AWA values greater than 3 degrees is considerably large. The calculated results for C D slightly over predict those from the experiments. Figure 4(c) shows the coordinates of the center of effort of the sails. The x and z coordinates of the geometric center of effort (x GCE and z GCE ) are.63m aft and 4.8m above the origin, which are indicated by alternate long and short dashed lines in the figure. It is seen that both the experimental and the calculated coordinates of x CE are near x GCE and move slightly forward with increasing AWA. Unfortunately, there is a wide scatter in the experimental values of z CE. This is thought to be because the measured Ks moment contains a large component from the mass of the dynamometer frame and rigging (659kg). This moment was subtracted from the measurement, taking into account the measured heel angle. If there is a slight error in the position of center of gravity of the dynamometer frame, or in the measured heel angle, the error in the calculated moment will be
C L, C D. (1) () Exp. Table ail shapes, measured experimental data and three-dimensional coordinates of the sails for the case of numbered point (1) in Figure 4 :C L :C D 1.5 (tb d) C L :C L :C D 1. Cal. (VLM) :C L :C D (RAN) C D :C L :C D 1 3 4 5 γ A (a) CL and CD vs. AWA C X, C Y Exp.. 1.5 1. C Y :C X :C Y (tb d) :C X :C Y Cal. (VLM) :C X :C Y (RAN) C X :C X :C Y 1 3 4 5 γ A (b) CX and CY vs. AWA x CE, z CE Exp. 7 66 44 z C E :x C E :z C E (tb d) :x C E :z C E Geometric zg C E Cal. (VLM) :x C E Geometric xgc E :z C E x C E (RAN) :x C E :z C E 1 3 4 5 γ A (c) xce and zce vs. AWA Figure 4 Performance variation as a function of apparent wind angle (AWA) for mainsail and 13% jib (1) 969335 AWA TWITDRAFT[%] AW[m/s] HEEL VB [kt] 3.7 15.5 8.6 6.9 15.1 5. C L C D C X C Y x CE z CE 1.44.8 1.39.41 4.17 % of 13%Jib Mainsail heit x y z x y z -3.78 46 1.3 -.81.136.934 1.3-1.843.7 1.8 1.3 % -.875.48.71 1.3 94 44 3.598 1.3 1.6.681 4.486 1.3 -.998.14.133 3.8 -.35.49.14.888.176 3.8-1.568.667.14 1.645.3 3.8 % -.85.795.14.46.4 3.8-7.861.14 3.173.363 3.8.76.886.14 3.947. 3.8 -.15 4.8.1 6.3-1.771.44 4.8.834.7 6.3 4-1.7.719 4.8 1.45.45 6.3 % -.73.85 4.8.81.483 6.3 -.145.898 4.8.7.44 6.3.448.898 4.8 3.371.331 6.3-1.433 6.4.38 8.8-1.186.33 6.4.761.18 8.8 6 -.893 7 6.4 1..389 8.8 % -5.715 6.4 1.699.47 8.8 -.176.79 6.4.191.46 8.8.17.83 6.4.691.41 8.8 -.65 8.56.396 11.3-41.17 8.56.651.144 11.3 8 -.414.318 8.56.914.61 11.3 % -5.419 8.56 1.19.33 11.3-73.486 8.56 1.476.36 11.3.1 35 8.56 1.768.374 11.3.13 1.7.483 13.8.144 16 1.7 11 1 13.8 1.159 3 1.7 38 3 13.8 %.173 44 1.7 67 33 13.8.189 56 1.7 95 4 13.8 7 66 1.7.64 51 13.8 large. However, though there is a scatter in the measured data, it can be seen that z CE is decreasing as AWA increases. The trends in the movement of both x CE and z CE as functions of AWA might be caused by the decrement of force acting on the aft and upper parts of the sails due to the loosening of main and jib sheets with increasing AWA. The calculated results for z CE obtained using theran-based CFD show the same trend as the experiments. On the other hand, the calculated results using VLM are considerably higher than the experimental ones. This might be caused by over estimation of the force acting on the upper portion of the mainsail. In this area, since the jib is not overlapping, flow separation may occur easily. However, the VLM does not take flow separation into account. The shapes and three-dimensional coordinates of the sails are given in Table. This shows the case of numbered point (1) in Figure 4. The figure described above the
table shows the sail section profiles at,, 4, 6 and 8% of the sail height. The three-dimensional coordinates of each section are given in the table. The origin of the coordinate of sail dynamometer system is shown in Figure 1. In this table, the positive direction of the x coordinate is aft. The four lines at the top of the table are the measured values for the wind and sail trim conditions, the boat attitude and the sail performance coefficients. In reference [7], the same tables are shown which are measured at various sail trim conditions. These tabulated data may provide a good benchmark for the validation of upwind sail CFD in full scale level. 4 AERODYNAMIC FORCE VARIATION DURING TACKING MANEUVER AND TACKING IMULATION 4.1 MEAUREMENT OF AERODYNAMIC FORCE VARIATION DURING TACKING MANEUVER Tacking of a sailing yacht is a quick maneuvering motion accompanied by large rolling angle changes in a short period of time. To analyze this type of large amplitude motion, a mathematical model for the simulation was proposed by Masuyama et al. [11,1]. The calculation method was applied to a 34-foot sailing cruiser and the simulated result showed good agreement with the measured data from full scale tests. However, in these research, the modeling of aerodynamic force variation during tacking was insufficient due to lack of information about the sail forces. In order to clarify the sail force variation during tacking maneuver, the measurements were conducted using Fujin [13, 14, 15]. Figure 5 shows two examples of the measured data in the time domain for X' d, Y' d, K' d and N' d during the tacking operation for seconds, from five seconds before to 15 seconds after the, where X' d and Y' d are the thrust and side force coefficients along the axes of sail dynamometer system, and K' d and N' d are the roll and yaw moment coefficients around the same axes. Figure 5(a) shows the case of tacking from starboard to port tack, and Figure 5(b) shows from port to starboard tack. The scattering of the data at the crossing points of the curves is caused by the crew action on the dynamometer frame in releasing and trimming the jib sheet during tacking. In the measured data, the inertia forces and moments due to the mass of the dynamometer frame are included. These effects clearly appear at the starting and finishing stage of the tacking maneuver, but are not so significant at the middle stage. Hence the measured data are indicated only subtracting the forces and moments due to the gravity force acting on the dynamometer frame using measured heel angle at every moment. Figure 6 shows the variation of sail force coefficients during tacking as a function of the heading angle of the boat, where = º means heading in the true wind direction. During tacking, the jib sheet was released just before the jib was backwinded on the new tack in order to minimize luffing of the jib and loss of wind power. The curves show the results of 1 tacking cases from starboard to port tack. It should be noted again that forces and moments are shown using the sail dynamometer coordinate system. The variations start from close hauled condition of starboard tack until the boat is on port tack, (i.e., from = -45º to 45º). The corresponding AWA, from γ A = 3º to -3º, are also indicated in the second abscissa in the figure. Figure 6(a) shows the variation of X' d. When the boat heads directly into the wind, X' d becomes about -.1, (i.e., drag force coefficient). Figures 6(b) to 6(d) show the forces and moments become zero not at =º, but around =1º, which indicates a delay in the variation of forces and moments compared to the change of heading angle. This could be caused by the sail filling with wind due to the yawing motion from the former tack to =1º on the new tack when the jib sheet was released. Inversely, for the case of port tack to starboard tack, the values of Y' d, K' d and N' d become zero at around = -1º, and the variation of forces and moments are almost symmetrical to Figure 6. From this result, it can be considered that the bias of the zero crossing point of the forces and moments at the tacking maneuver is symmetrical. 4. MODEL OF AIL FORCE VARIATION FOR TACKING IMULATION Let us define the model of sail force variation for the tacking simulation as bold lines in Figure 7 referring to the measured data in Figure 6. Figure 7(a) shows the case of tacking from starboard to port tack. The abscissa indicates AWA (γ A ). In the model, the basic sail performance curves of X's and Y's are divided into three stages. tage A is the range of γ A that is greater than º. In this region, the coefficients vary with γ A according to the basic curves. tage B is the range of γ A = º to -1º. In this region, the coefficients are assumed to vary linearly along the lines determined from the results of Figures 6(a) and 6(b). tage C is the range of γ A = -1º to -3º. In this region, the basic pattern of the coefficients is expressed as basic performance curves. However, it may take several seconds to recover to the basic curves due to the delay of trimming the sails for the new tack condition. Therefore, the coefficients are assumed to increase from the lowest values to the basic curve values with elapsed time. The recovery time was chosen from 5 to 1 seconds by taking the simulated heel angle corresponding to the measured one. Figure 7(b) shows the case of tacking from port to starboard tack. In this case the variation pattern proceeds in the opposite direction. The sail forces and moments expressed in equation (1) are used for the equations of motion in the following chapter. 4.3 EQUATION OF MOTION FOR TACKING IMULATION In order to express the large amplitude motion such as a tacking maneuver of a sailing yacht, the authors
1.5 1.5 X' d, Y' d, K' s d, N's d 1. - X' d K' d N' d X' d, Y' d, K' d, N' d 1. - K' d X' d N' d Y' d -1. -1. Y' d -1.5-5 5 1 15 (a) Tacking from starboard tack to port tack -1.5-5 5 1 15 (b) Tacking from port tack to starboard tack Figure 5 Examples of measured sail force coefficients in the time domain during tacking operation 1. 1. P X' d P K' d - - -6-4 - 4 6 3 1-1 - -3 (a) X' d vs. and γ A γ A -1. -6-4 - 4 6 3 1-1 - -3 (c) K' d vs. and γa γa 1.5 Y' d 1. P N' d P - -1. -1.5-6 -4-4 6 γ A - -6-4 - 4 6 3 1-1 - -3 3 1-1 - -3 γa (b) Y' d vs. and γ A (d) N ' d vs. and γ A Figure 6 Variation of sail force coefficients during tacking operation as a function of of boat (tacking from starboard to port tack) heading angle X',Y'. tarboard tack A B 1.5 C 1. X' Port tack Y' Increasing with tarboard tack X' C X',Y'. 1.5 B 1. Port tack A Y' X' X' 5 4 3 1-1 - -3-4 -5 - -1. γ A [d eg] 5 4 3 1-1 - -3-4 -5 γa Increasing with - -1. Y' Y' -1.5 =-45 =45 =-45 -. (a) tacking from starboard to port tack -1.5 =45 -. (b) tacking from port to starboard tack Figure 7 Model of sail force variation during tacking maneuver for tacking simulation
employed equations of motion expressed by the horizontal body axis system introduced by Hamamoto et al. [16]. The origin of the coordinate system is on the C.G. of the boat which is shown in Figure 1. The x-axis lies along the centerline of the boat on the still water plane and is positive forward. The y-axis is positive to starboard in the still water plane. The z-axis is positive downwards. In this coordinate system, the maneuvering motion of the boat and aero/hydro-dynamic forces acting on it can be expressed in the horizontal plane even though the boat heels. Both added mass and added moment of inertia, which are referenced to the body axes fixed on the boat, can be obtained by the coordinate transformation. Then, the equations of motion expressed in the horizontal body axis system for the motions of surge, sway, roll and yaw are derived as follows. The left sides are forces and moments due to the mass and added masses of the boat, and the right sides are fluid dynamic forces and moments acting on the hull and sail with reference to the horizontal body axes. surge: m mx U ( ) ( m my cos mz sin ) V (1) X X X V X X sway: ( m m roll: ( I J xx yaw: ( I y xx J Y cos m ) ( I H z z H y V sin ) V ( m m ) U ( m m )sin cos V ( I K H J N Y Y Y J K K H )sin ( I ) ( I ) ( I R J R R x Y J ) sin cos K mggm sin J N N R N ) cos ) sin cos The derivation of these equations and calculation method of each term are described in detail in references [14, 15]. () (3) 4.4 COMPARION BETWEEN MEAURED AND IMULATED REULT The simulation method was applied to several boats and the results showed good agreement with the measured data. In this report, the cases of Fujin and Fair V are shown in the following sections. The Fair V is a 34-foot sailing cruiser, which was designed by the author and used for the first measurement of tacking maneuver. The Runge-Kutta method was employed to calculate the equations of motion. The rolling and yawing motions were calculated around the C.G. of the boat. Input data for the simulation is true wind velocity and the measured time history of rudder angle during tacking maneuver at increments of.1 seconds. (4) 4.4.1 Results of Fujin Figure 8 shows the comparison between measured and simulated results of Fujin. Figure 8(1) shows tacking from starboard to port tack, and 8() shows tacking from port to starboard tack. The sail force variations in Figures 5(a) and 5(b) correspond to these cases, respectively. The indicated results were recorded for 35 seconds, beginning 5 seconds before the. Figure 8(1)(a) shows the boat trajectories. olid circles indicate the positions of measured C.G. of the boat at each second, while open circles indicate the simulated positions. The illustrations of the small boat symbol indicate the heading angle every three seconds. The wind blows from the right side of the figure and the grid spacing is taken as 15 meters. Figure 8(1)(b) shows the time histories of rudder angle, heading angle, heel angle and boat velocity V B. The solid lines are measured data and the dotted lines are simulated data. In Figures 8(1)(b) and 8()(b), the patterns of rudder angle variation can be considered as standard for tacking maneuvers. As shown, tacking with a yawing motion of 9 degrees is completed in 7 to 8 seconds. The boat velocity decreases about 3%, and the boat takes about 15 seconds to recover to the previous velocity after the yawing motion is completed. The measured time histories of and indicate the delay of zero crossing point of compared with. This might be caused by the sail filling with wind due to the yawing motion until around = 1º on the opposite tack as shown in Figure 6. The simulated time histories show a slight delay when compared to the measured data. In particular, the delay of the simulated heel angle is relatively large. This might be caused by the over-estimation of the damping coefficient for rolling, K. For this point further investigation might be necessary. However, the simulated results of velocity decrement show agreement with the measured results. This suggests that the model of sail force variation proposed in this report is adequate for the tacking simulation. In Figures 8(1)(a) and 8()(a), although the simulated trajectories show slightly larger turning radiuses than the measured trajectories, the simulated results show agreement with the measured values overall. 4.4. Results of Fair V Figure 9 shows the comparison between measured and simulated results of Fair V. The contents of these figures are identical to Figure 8. In these cases, the rudder angle variations in the first stage are relatively small. These cause the delay of yawing motion of the boat. Hence it takes more than 1 seconds to complete the tacking maneuver. On the other hand, the simulated results show a prompt response to the rudder angle variation. Therefore the simulated time histories vary slightly earlier compared with the measured histories. By the same reasoning, the simulated trajectories in Figures 9(1)(a) and 9()(a) show smaller turning radiuses than the measured trajectories.
measured simulated measured simulated U T=5.7m/s start of tacking U T=5.4m/s start of tacking 15m 15m 7 35-35 (a) Trajectory of boat [m/s] 5-7 -5 5 1 15 5 3 (b) Boat attitude parameters V B 4 3 1 VB 7 35-35 V B (a) Trajectory of boat : Heading Angle : Heel Angle : Rudder Angle VB: Boat Velocity [m/s] 5-7 -5 5 1 15 5 3 (b) Boat attitude parameters (1) From starboard to port tack () From port to starboard tack Figure 8 Measured and simulated results of tacking maneuver of Fujin 4 3 1 VB measured simulated measured simulated UT=4.8m/s start of tacking U T=4.9m/s start of tacking 15m 15m 7 35-35 (a) Trajectory of boat [m/s] 5-7 -5 5 1 15 5 3 (b) Boat attitude parameters VB 4 3 1 VB 7 35-35 V B (a) Trajectory of boat : Heading Angle : Heel Angle : Rudder Angle VB: Boat Velocity [m/s] 5-7 -5 5 1 15 5 3 (b) Boat attitude parameters (1) From starboard to port tack () From port to starboard tack Figure 9 Measured and simulated results of tacking maneuver of Fair V 4 3 1 VB
Overall, although the timing of boat motion indicated in the simulated time histories shows a slight discrepancy, the tendency and amount of variation of the boat motion indicate good agreement with the measured data, including the decrement of boat velocity. 5 ROLE OF FULL CALE TET A THE BRIDGE BETWEEN MODEL TET AND CFD Wind Tunnel tests using model sails are commonly performed at the Reynolds number (Re) region of around x1 5 to 5x1 5. This region is referred to as the critical Reynolds number range, where the boundary layer flow turns from laminar to turbulent, causing the drag and lift coefficients change drastically. Hoerner [17] shows experimental results of wing sections in this region and indicates that the maximum lift coefficient varies as a function of the Reynolds number, camber ratio and noseradius ratio, and also can be very sensitive to the test conditions. From the author s experience of wind tunnel tests [18], the unexpected and unstable deviation on measured data occurred in particular in the case of downwind sail. Normally, a spinnaker has a large camber and a sharp leading edge which works at a high entrance angle. This causes the laminar-type separation at the suction side of the leading edge at the low Reynolds number region. When this separation area spreads over the surface of the suction side, the drag and lift coefficients change drastically. The author sometimes experienced that the slight shape change of a spinnaker by sheet trimming caused serious deviation on measured data. Therefore, it should be considered that the wind tunnel test in this Reynolds number region has to be performed very carefully. On the other hand, for the full scale boat, the sails work in the Reynolds number of almost greater than 1x1 6. In this region, although the effect of critical Reynolds number still remains, the effect on the measured data may be less than the case of wind tunnel tests. Recently, Viola et al. [19] measured the pressure distribution on the surface of full scale downwind sails during sea tests using a Platu5-class yacht. The results were compared with the measured data by wind tunnel tests, and showed very interesting differences in the pressure distributions near the leading edge. The author thinks this is the first report which points out the differences of pressure distribution on the downwind sails between full scale and scale model. It can be considered that this fact indicates the importance of full scale measurements for the developments of downwind sails. A sail dynamometer boat may provide more precise information not only about pressure distribution, but also aerodynamic forces and sail shapes simultaneously in full scale level. Investigation of effect on the sail aerodynamic forces by dynamic motion of the boat is another important research target of the full scale test using a sail dynamometer boat. The research of aerodynamic force variation during tacking maneuver should be broadened to investigate the best tacking procedure. The motions of pitching and rolling of a boat also have a serious effect on sail performance. For the research of these effects, a sail dynamometer boat will provide essential information. When the sail tests were performed using Fujin, it was difficult to measure the shape of sail such as balloon spinnaker simultaneously with aerodynamic forces. However, recently we can easily employ high performance digital cameras and 3-dimensional shape analyzing systems. Moreover, the developments of measurement systems such as small gyroscope, GP sensor, electronics transmitter, etc. can also provide us good opportunities for carrying out sea tests easily. It is worth emphasizing that the tests using a sail dynamometer boat can provide the ultimate validation data for CFD in full scale level. Now, a new generation sail dynamometer boat is being prepared by Professor Fabio Fossati at Politecnico di Milano. We are looking forward to the results of this boat from tests at Lake Como in Italy. 6 CONCLUION The work achieved with the sail dynamometer boat Fujin was reported. At first, the sail shapes and performance for upwind conditions were measured in steady sailing conditions. The results were compared with the numerical calculations using the measured sail shapes as the input data. The database of three-dimensional coordinates of the sail shapes was also tabulated with the aerodynamic coefficients. The sail shape database and the comparison with the numerical calculations indicated in this research provide a good benchmark for the validation of sail CFD in full scale level. Then, the aerodynamic force variation during tacking maneuvers was measured by Fujin, and a new simulation model of tacking maneuver was proposed. The simulated results showed good agreement with the measured data. Finally, the scale effect problem of wind tunnel tests was discussed. Wind tunnel tests using model sails are performed at the region of critical Reynolds number. Therefore, the wind tunnel test in this Reynolds number region had to be performed very carefully. On the other hand, the full scale tests using a sail dynamometer boat are free from scale effect problems and appear more promising. ACKNOWLEDGEMENT The author wishes to thank Professor T. Fukasawa at Osaka Prefecture University and Dr. Y. Tahara at National Maritime Research Institute of Japan for their contributions as co-researchers. The author also would like to thank Mr. H. Mitsui, the former harbour master of the Anamizu Bay eminar House of Kanazawa Institute of Technology, for his assistance with the sea trials. Help with the sea trials given by graduate and undergraduate students of the Kanazawa Institute of Technology is also acknowledged.
REFERENCE 1. MILGRAM, J. H., PETER, D. B. and ECKHOUE, D.N., N., Modeling IACC ail Forces by Combining Measurements with CFD, 11th Chesapeake ailing Yacht ymposium, NAME, 1993.. HOCHKIRCH, K. and BRANDT, H., Fullscale Hydrodynamic Force Measurement on the Berlin ailing Dynamometer, 14th Chesapeake ailing Yacht ymposium, NAME, 1999. 3. HANEN, H., JACKON, P. and HOCHKIRCH, K., Comparison of Wind Tunnel and Full-scale Aerodynamic ail Force, International Journal of mall Craft Technology (IJCT), Vol. 145 Part B1: 3-31, 3. 4. KREBBER, B. and HOCHKIRCH, K., Numerical Investigation on the Effects of Trim for a Yacht Rig, nd High Performance Yacht Design Conference, Auckland, New Zealand, 6. 5. MAUYAMA, Y. and FUKAAWA T., Full cale Measurement of ail Force and the Validation of Numerical Calculation Method, 13th Chesapeake ailing Yacht ymposium, NAME, 1997. 6. MAUYAMA, Y., TAHARA, Y.,FUKAAWA, T. and MAEDA, N., Database of ail hapes vs. ail Performance and Validation of Numerical Calculation for Upwind Condition, 18th Chesapeake ailing Yacht ymposium, NAME, 11-31, 7. 7. MAUYAMA, Y., TAHARA, Y.,FUKAAWA, T. and MAEDA, N., Database of ail hapes versus ail Performance and Validation of Numerical Calculation for the Upwind Condition, Journal of Marine cience and Technology, JANAOE, vol. 14, No., 137-16, 9. 8. FUKAAWA, T., Aeroelastic Transient Response of 3-Dimensional Flexible ail, Aero-Hydroelasticity, ICAHE'93, 1993. 9. TAHARA Y., Evaluation of a RaN Equation Method for Calculating hip Boundary Layers and Wakes Including Wave Effects, J. ociety of Naval Architects of Japan 18: 59-8, 1996. 1. TAHARA, Y., HAYAHI, G., Flow Analyses around Downwind-ail ystem of an IACC ailing Boat by a Multi-Block N/RaN Method, J. ociety of Naval Architects of Japan 194: 1-1, 3. 11. MAUYAMA, Y., NAKAMURA, I., TATANO, H. and TAKAGI, K., Dynamic Performance of ailing Cruiser by Full-cale ea Tests, 11th Chesapeake ailing Yacht ymposium, NAME, 161-179, 1993. 1. MAUYAMA, Y., FUKAAWA, T. and AAGAWA, H., Tacking imulation of ailing Yachts-Numerical Integration of Equations of Motion and Application of Neural Network Technique, 1th Chesapeake ailing Yacht ymposium, NAME, 117-131, 1995. 13. MAUYAMA, Y. and FUKAAWA, T., Tacking imulation of ailing Yachts with New Model of Aerodynamic Force Variation, 3rd High Performance Yacht Design Conference, Auckland, 138-147, 8. 14. MAUYAMA, Y. and FUKAAWA, T., Tacking imulation of ailing Yachts with New Model of Aerodynamic Force Variation During Tacking Maneuver, Journal of ailboat Technology, NAME, 1-. 1. 15. MAUYAMA, Y. and FUKAAWA, T., Tacking imulation of ailing Yachts with New Model of Aerodynamic Force Variation During Tacking Maneuver, Transactions, NAME, Vol. 119. 11. 16. HAMAMOTO, M. and AKIYOHI, T., tudy on hip Motions and Capsizing in Following eas (1st Report), Journal of The ociety of Naval Architects of Japan, No.147, 173-18, 1988. 17. HOERNER,. F., and BORT, H. V., Fluiddynamic Lift, Hoerner Fluid Dynamics, p.4-1, 1975. 18. TAHARA, Y., MAUYAMA, Y., FUKAAWA, T. and KATORI, M., CFD Calculation of Downwind ail Performance Using Flying hape Measured by Wind Tunnel Tests, 4th High Performance Yacht Design Conference, Auckland, 38-47, 1. 19. VIOLA, I. M. and FLAY, R. G., ail Aerodynamics: On-Water Pressure Measurements on a Downwind ail, Journal of hip Research, NAME, Vol.56, No.4, 197-6, 1. AUTHOR BIOGRAPHY Y. Masuyama is a Professor Emeritus and a Research Fellow at the Actual eas hip and Marine Research Laboratory, Kanazawa Institute of Technology, Japan. He graduated from the Department of Mechanical Engineering, Toyama University, and received a degree of Doctor of Engineering from Osaka University. He learned the yacht design process at the Kumazawa Craft Laboratory, yacht design office, and has been continuing research about sailing yachts at Kanazawa Institute of Technology. His research interests include sail performance, velocity prediction, maneuverability and stability of sailing yachts. He had been involved with the technical committee of the Japanese America s Cup challenge team Nippon Challenge. He was a chairman of the ailing Yacht Research Association of Japan from 1993 to 1.