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Science of the 470 Sailing Performance

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Science of the 470 Sailing Performance Journal of Sailing Technology 2020, volume 5, issue 1, pp. 20 - 46. The Society of Naval Architects and Marine Engineers. Science of the 470 Sailing Performance Yutaka Masuyama Kanazawa Institute of Technology, Kanazawa, Japan. Munehiko Ogihara SANYODENKI AMERICA, INC. Torrance CA, USA, [email protected]. Manuscript received July 9, 2019; revision received April 6, 2020; accepted July 26, 2020. Downloaded from http://onepetro.org/jst/article-pdf/5/01/20/2478407/sname-jst-2020-05.pdf by guest on 25 September 2021 EDITORIAL NOTE By J.-B. SOUPPEZ, on behalf of the Journal of Sailing Technology’s Editorial Board. This paper holds a significant place in the Journal of Sailing Technology, as the very last publication of Prof. Masuyama, published posthumously, and co-authors by Dr Ogihara. For many decades, Prof. Masuyama has been a very influential and respected member of the sailing yacht research community world-wide, holding the chairmanship of the Sailing Yacht Research Association of Japan for close to 20 years, and being involved with the Japanese America’s Cup Challenge. His expertise and academic research have impacted generations of researchers, and his work on high performance sails, sailing yachts and velocity prediction remains at the forefront of sailing technology. It is therefore with great honour that the Journal of Sailing Technology presents the very last insights of Prof. Masuyama into the sailing performance of the 470 Olympic class dinghy. ABSTRACT. The paper presents a Velocity Prediction Program (VPP) for the 470 dinghy. Starting from a description of the hull performance and sail performance, measured and predicted performance are compared, including the effect of the spinnaker. These results will guide sailors towards enhanced performance in the future. Keywords: 470; aerodynamics; hydrodynamics; maneuvering; planing; tacking; Tokyo Olympic. NOMENCLATURE A Sail area (m2) B Breadth at design waterline (m) CD Drag force coefficient CL Lift force coefficient CN Yaw moment coefficient CT Resistent coefficient D Design draft (including centerboard 1.08 m) (m) Fn Froude number K, N Moments about X- and z-axis in horizontal body axis system (kgf m) KTrapeze Righting moment of Trapeze (kgf m) L Length on design waterline (4.4 m) S Wetted area (4.52 m2) T Resistance (kgf) U, V Velocity components along x- and y-axis in horizontal body axis system (knots or m s-1) -1 UA Apparent wind speed (knots or m s ) -1 UT True wind speed (knots or m s ) -1 VB Boat velocity (knots or m s ) 20 VMG Velocity Made Good (knots or m s-1) X, Y Force components along x- and y-axis in horizontal body axis system (kgf) ZCE Vertical coordinate of the centre of effort (m) β Leeway angle (deg) γA Apparent wind angle (deg) γT True wind angle (deg) δ Rudder angle (deg) φ Heel angle or roll angle (deg) ψ Heading angle (deg) -3 ρa Density of air (kg m ) -3) ρw Density of water (kg m Δ GZ Righting moment (without trapeze) (kgf m) AWA Apparent wind angle AWS Apparent wind speed Downloaded from http://onepetro.org/jst/article-pdf/5/01/20/2478407/sname-jst-2020-05.pdf by guest on 25 September 2021 CB Centre of buoyancy CE Centre of effort CG Centre of gravity GPS Global position system TWA Trues wind angle TWS True wind speed VPP Velocity prediction program 1. INTRODUCTION The 470 (Four-Seventy) was designed in 1963 by the Frenchman Andre Cornu as a double-handed mono-hull planing dinghy. The name comes from the overall length of the boat in centimeters (470 cm). The 470 is a World Sailing International Class has been an Olympic class since the 1976 games. In Japan, the 470 is used in university championships and National Athletic meets. So, it is in the most popular dinghy races in Japan. Ideal crew weight of skipper and crew is 130 kg, it is suitable for Japanese who are smaller than Europeans and Americans. This paper progresses the science of the sailing performance of the 470 concerning to aspects such as hull performance, sail performance, steady sailing performance, and maneuvering performance. Specification of the 470 Table 1 presents the technical details, Figure 1 shows the Sail plan, and Figure 2 depicts the hull shape (Japan 470 class association, 2019). The 470 has a very flat hull form. This flat hull implies that the hull form in the wetted area and submerged area variations are much dependent on the trim angle (pitch angle) and heel angle, which is considered to affect the performance as well. Figure 3 shows the result of the calculation of displacement and wetted area variations for draft depth from the hull shape of Figure 2. The abscissa indicates draft depth. The vertical axis shows the displacement △ and wetted area ◆. When the gross weight, including the crew and skipper, is 250 kgf, the draft depth is about 0.15 m, and the wetted area is about 3.8 m2. Also, when the gross weight variation is 35 kgf, the draft depth variation is 1 cm, and the wetted area variation is 0.25 m2. 21 Table 1. TechnicaL detaiL of 470. Length: 4.7m Length of waterline: 4.4m Weight: 120kg Mast: 6.76m Main: 9.12m2 Jib: 3.58m2 Spinnaker: 13.0m2 Downloaded from http://onepetro.org/jst/article-pdf/5/01/20/2478407/sname-jst-2020-05.pdf by guest on 25 September 2021 Figure 1. SaiL plan of 470. Figure 2. HulL shape of 470. 22 Downloaded from http://onepetro.org/jst/article-pdf/5/01/20/2478407/sname-jst-2020-05.pdf by guest on 25 September 2021 Figure 3. Draft depth - displacement - wetted area. Figure 4 shows the calculated stability. The abscissa indicates the heel angle. The vertical axis shows stability. The gross weight, including the crew (70 kgf) and the skipper (60 kgf), is 250 kgf. However, the skipper can hike out. So, the CG of the crew is 2 m away from the hull centerline as of 90 kgf (70 kgf x 1.3). Dashed line shows without trapeze. The solid line shows full trapeze. Shape of HulL From Figure 4, without trapeze, the maXimum righting moment is achieved at a heel angle of about 30°, but it is small as 60 kgf m. On the other hand, when trapeze is performed, it becomes the maXimum righting moment of about 220 kgf m at a heel angle of 25°. However, since the righting moment decreases at a further heel angle, the range of the heel angle that can be restored is surprisingly narrow. In the case of the cruiser, since the ballast keel is around 40% of the hull weight on the bottom of the ship, the righting moment will continue to increase to about 50° in the heel angle. These are the reason why dinghy can capsize more quickly than a cruiser. Heeling moment decreases with heel angle because heel decreases the effective angle of attack of sail. The cross point of the heel moment curve is obtained under this condition when the righting moment curve of the hull becomes a balance point, that is, a steady sailing state. In the case of TWS 6 m, the heel angle is balanced at about 10°. The symbol ☓ indicates TWS 8 m s-1, and the sail is full power. Where ☓ intersects the righting moment of the blue line at heel angle 45°, and the righting moment is already decreasing, the boat will capsize at once with a kinetic energy that makes it heel to 45°. In the case of power down sail to 70% (△), the heel angle is balanced at about 20°. Based on the above, the following can be concluded, a 470 dinghy with righting moment by trapeze has little increase in righting moment by the heel, the maximum righting moment is at about a heel angle of 25° (side deck touches the water). As soon as the side deck begins to touch the water, it is necessary to immediately reduce the power of sail or luffing up to avoid capsize. In actual sailing, the heeling moment which acts to increase heel is generated by the force of water acting on the hull (especially centerboard). For this reason, it is necessary to consider the moment of restoration of the hull by 10 to 20% lower than the value shown in Figure 4. 23 Downloaded from http://onepetro.org/jst/article-pdf/5/01/20/2478407/sname-jst-2020-05.pdf by guest on 25 September 2021 Figure 4. Righting moment/HeeL moment. 〇: TWS 6 m s-1, Sail Full Power, TWA: 60°, AWA: 40°, AWS: 8.5 m s-1. △: TWS: 8 m s-1, Sail 70% Power, TWA: 60°, AWA: 40°, AWS:10.7 m s-1. Heel moment was calculated as 70%). ☓: TWS 8 m s-1, Sail Full Power, TWA: 60°, AWA: 40°, AWS:10.7 m s-1. Tacking Maneuver Figure 5 and 6 shows the dynamic measurement result of tacking maneuver. Figure 5 (a) and 6 (a) show the variation of the rudder angle (δ) and heading angle (ψ) for 25 s from 5 s before tacking. Figure 5 (b) and 6 (b) show the variation of the VB. Figure 5 (c) and 6 (c) show the variation of the boat trajectories. Circles indicate the position of the center of the boat at each second. The illustration of the small boat symbol indicates the heading angle every two seconds. The wind blows from the top of the figure, and the grid spacing is taken as 10 m. Red shows the case where the rudder used gently, and the maX rudder angle is up to 45°.
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