12 AERODYNAMICAL EXPERIMENTS UPON A YACHT'S MAINSAIL. 



Mr. Nathaniel G. Herreshoff, Member (Communicated) : — I have received Mr. 

 Everett's paper on yacht sails and have read it with a great deal of interest, and am sorry I 

 cannot be at the meeting. There is a great deal to be learned about the driving powers of 

 sails, and I think this paper has opened up the subject in a very good way. I hope such exper- 

 iments will be continued and include such matters as taking into account the efifect of dif- 

 ferent amounts of bag of draft, for different velocities of wind, the effect of the inclination of 

 the mast, twist of sail, etc. 



Mr. H. de B. Parsons, Member (Communicated) : — Having read with interest Profes- 

 sor Everett's paper giving results of experiments upon a yacht's mainsail, the speaker is 

 pleased that experiments of this nature are being undertaken. 



In the design of a racing yacht, success largely depends on the proper locations of the 

 centers of wind pressure of each sail in order that the vessel may be properly balanced, espe- 

 cially when sailing to windward. So much depends upon the cut of the sails that experiments 

 on one mainsail are probably not sufficient to accurately determine a formula for the location 

 of the true center of pressure. Variations in shape, which result in a flat or loose-fitting 

 sail, and heel of the vessel must necessarily affect the location of the actual center of 

 pressure. 



The writer was much interested in the description of the wind tunnel and he takes 

 pleasure in contributing the following information with regard to a wind tunnel which he 

 designed. 



In 1913 the writer had occasion to make experiments on the power developed by a 

 new type of wind-mill, known as an air turbine. In order to determine suitable angles for 

 the sails or vanes, the writer designed a testing apparatus, shown on Plate 13, which con- 

 sisted of a circular, galvanized-iron tunnel, 8 feet in diameter by 38 feet in length. An arti- 

 ficial wind was created through this tunnel by a 96-inch disc fan, driven by an electric motor. 

 By varying the speed of the motor and by changing the size of the pulleys, it was possible to 

 obtain a wide range of air velocities, or wind, through the tunnel. 



Baffies were arranged inside the tunnel, located about 8 feet behind the fan, so as to 

 straighten out the flow of air and prevent eddies and swirls. Various forms of baffles were 

 tried, but the one finally adopted consisted of thin wooden vanes, arranged as shown on 

 Plate 13. These baffles worked well and gave satisfactory results, as was proven by tests 

 made with an anemometer and with a delicate pitot tube. Readings with both the ane- 

 mometer and pitot tube were made at many points in the cross-sectional area of the tunnel, 

 and the readings obtained were consistent and showed a steady breeze. 



The model under test was placed near the free end of the tunnel, and air measurements 

 were made in front of the model by a pitot tube, which had been standardized, as mentioned 

 before, by teing operated in connection with an anemometer. 



The whole apparatus had to be located out of doors. The end at which the fan was 

 located was enclosed by a shed, so as to protect the fan and motor from the weather. The 

 free end of the tunnel entered a chamber, the sides of which were carried up sufficiently high 

 to prevent the natural wind from interfering with the artificial wind created by the fan. 



The whole apparatus, as shown on the plate, cost about $1,000 erected and ready for 

 test. 



The writer does not offer his design as being better than the one described by Professor 

 Everett, but thought that a record of another wind tunnel, as actually constructed, might be 

 of interest to members of the Society. 



