Investigations on Sail Force by Full Scale Measurement and Numerical Calculation

Abstract

Sail forces were measured in a full-scale sailing boat with the use of a sail force dynamometer. This apparatus consisted of an aluminum frame fixed to the hull by way of several load cells. The sailing boat was modified so that the dynamometer frame could be installed inside the hull. The mast, stays, winches, and other sailing rig were fixed on the frame so as to transmit all the forces acting on sail to the frame. By transforming the measured forces, the lift force, drag force, thrust, side force, or the center of effort of the sail force could be obtained. The sailing conditions of the boat, such as the boat speed, heel angle, wind speed, wind angle, and so on, were also measured.Sail shapes of the boat in the up-wind condition were also measured with the use of CCD cameras installed in the boat. The sail shape images taken by the cameras were transformed to bit-map files, and then processed by an SSA-2 D, a sail shape analyzing software. With the use of this software, sail shape parameters were obtained. The relationship between the measured sail forces and the sail shape parameters is discussed in this paper. Moreover, the measured sail shapes were used as the input data for the numerical calculations.Numerical calculations were performed to estimate the sail forces of the boat. In the calculations, two sails, a mainsail and a jib, were modeled in the form of a vortex lattice. The vortex lattice method was adopted as the numerical calculation method. Step by step calculations were conducted up to attaining the steady state of the sail in steady wind. Calculated sail forces were compared with the measured forces, and the validity of the numerical method was studied. 17) "International Measurement System (IMS)", Offshore Racing Council, 1996

Sail Performance Analysis of Sailing Yachts by Numerical Calculations and Experiments

“…The location of wake vortices are determined by the condition that they are free vortices; that is, the stream line of wake vortices should be parallel to the velocity field induced by total vortex system. A step-by-step procedure developed by Fukasawa was adopted in this paper to determine the strength of the bound vortices and the location of wake vortices Fukasawa & Katori, 1993;Masuyama et al, 1997aMasuyama et al, , 1997b. The wake vortices are shed from the trailing edge in each time step according to Helmholtz's theorem; that is,…”

“…Such studies on sail force measurements were performed by Milgram et al (1993), Masuyama et al (1997aMasuyama et al ( , 1997b, and Hochkirch et al (1999), who built full-scale boats with onboard sail dynamometer systems. Milgram (1993) showed in his pioneering work that the sail dynamometer boat, Amphetrete, is quite capable.…”

“…Masuyama and Fukasawa were encouraged by Milgram's work, and built a sail dynamometer boat, Fujin. The measurement system installed in the Fujin and the results of calibration test and sailing test were reported by Masuyama et al (1997a and1997b).…”

“…The under deck portion of the mast is held by the frame, and the other rig components are attached to the frame through the deck holes. The data acquisition system and calibration method for the Fujin were described by Masuyama et al (1997a and1997b). The sail shape was recorded using pairs of CCD cameras.…”

“…The AAF is a specialized package for the calculation of sail performance of sailing yachts, and composed of both mesh generator and post analyzer. The sail shapes and performance were measured using a sail dynamometer boat Fujin under sailing condition on the sea (Masuyama et al, 1997a(Masuyama et al, , 1997b. Fujin is a 34-foot LOA boat, in which load cells and CCD cameras were installed to simultaneously measure the sail forces and shapes.…”