Articles

The Journal of Sailboat Technology will be available free of charge to all members of SNAME; for a limited time articles will be free to the public.

Experimental Investigation of Sail Aerodynamic Behavior in Dynamic Conditions.
By Fabio Fossati and Sara Muggiasca.

Abstract: The aerodynamic behavior of a 48’ yacht rig 3D scale model was characterized by means of wind tunnel tests. The experimental program, performed in the Politecnico di Milano Twisted Flow Wind Tunnel, allowed the aerodynamic forces to be characterized using forced motion tests and the aeroelastic behavior of the sail plan to be studied. Preliminary results are presented with reference to the typical encounter frequency range and typical pitch amplitudes corresponding to best yacht Velocity Made Good (VMG) condition for different true wind speeds and related sea states. A new representation of the aeroelastic effects is proposed in the form of aerodynamic hysteresis loops, obtained by plotting the sail plan aerodynamic coefficients against instantaneous apparent wind angle, varied using a harmonic law combining wind tunnel constant wind speed with sail plan center of effort velocity induced by yacht pitch motion. A “sail plan reduced velocity” concept is defined, and experimental results show that this reduced velocity play a fundamental role in sail plan aerodynamics. Finally, an estimate of the aerodynamic added mass effects is provided based on the comparison between the measured pitch moment during the “wind off” tests and the experimental test rig pitch moment of inertia.
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Tacking Simulation of Sailing Yachts With New Model of Aerodynamic Force Variation During Tacking Maneuver.
By Yutaka Masuyama and Toichi Fukasawa

Abstract: A mathematical model for the tacking maneuver of a sailing yacht is presented as an extension of research by the same authors. The authors have proposed the equations of motion for the tacking maneuver expressed in the horizontal body axis system. 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, the modeling of aerodynamic force variation during tacking was insufficient due to lack of information about the sail forces. In this report, the authors performed full-scale measurement of sail forces during tacking maneuvers using a sail dynamometer boat Fujin. The Fujin is a 34-foot sailing cruiser which has a measurement system to obtain simultaneously sail forces, sail shapes, and boat attitude. Based on the results of full-scale measurements, a new model of aerodynamic force variation for the tacking maneuver was proposed. The equations of motion were also simplified to more easily perform the numerical simulation. Using this calculation method, the tacking simulations were performed and compared with the measured data from three full-scale boats. The simulated results showed good agreement with the measured data. This simulation method provides an effective means for assessment of tacking performance of general sailing yachts.
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Experimental Study of the Hydro-Impact of Slamming in a Modern Racing Sailboat.
June Lee and Philip A. Wilson.

Abstract: The hydrodynamic impact, or hydro-impact, phenomenon caused by slamming on racing yachts and the local structure’s response is studied experimentally. Pressure transducers and a special measurement system named ‘Slam Patch’ have been designed and implemented to measure the hydro-impact pressure and/or the local structure’s response. The measurement systems were installed on a 1/7-scale model of an Open 60 yacht. Modal, rotational drop, and seakeeping-slamming tests are carried out. The measured hydro-impact pressure was processed statistically. A methodology to scale up the test results to prototype is mentioned. At the same time, the transient response of a simple structure under half-sine impulse is calculated using a commercial finite element analysis program to study the effect of the relationship between impulse duration and natural frequency of the structure.
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