AERODYNAMICAL EXPERIMENTS UPON A YACHT'S MAINSAIL. 11 



I had the pleasure of seeing Professor Everett making one of his experiments and also 

 of examining very carefully the sail he used. This sail was a model of one that has been 

 successful in practice, and was in keeping with the present idea of the form. The form, which 

 he does not describe in his paper, has a moderate amount of curvature or draft with the 

 greatest amoimt of curvature forward and the least aft. The aim of the sail-makers at 

 the present time is to get as near a parabolic form as possible. In making his experiments, 

 Professor Everett had a very good example of modem sail making. 



The results of his experiments are interesting as the geometrical center of the sail is 

 practically in the same position as the center of pressure, the slight difference, both vertically 

 and in a horizontal direction, being easily accounted for by the windage of the mast. This 

 shows that the draft or form was about right for the wind velocity used, as the pressure must 

 have been even throughout the sail. 



A number of questions have been under discussion for a long while. One of them is, as 

 to whether the draft should be the same at all times. Some contend that you should have a 

 moderate draft for heavy winds, a medium draft for medium winds, and a considerable draft 

 for light winds. Others contend that the sail with a moderate draft, but perfectly made, 

 is the best one under all conditions. 



I hope Professor Everett will be able to carry on his experiments, or, if he cannot do so, 

 that some one else will take up the work and try, say, three sails with different amounts of 

 draft and try each of these at different wind velocities, so that we will get the further infor- 

 mation that we very much need. 



This paper is of great value to the naval architect, and of possibly greater value to the 

 practical sailorman. From the data contained a dial could easily be made, having two hands, 

 with two rows of corresponding figures on the circumference. Having set one hand at the 

 angle of apparent wind, the other hand could be set at the corresponding figure. This hand 

 would then give the proper angle of boom for the direction of boat and apparent wind. With 

 such a dial, sail trimming can be brought to an exact science. In the past it has been a 

 matter of judgment and experience. 



As I said before, I hope these experiments can be continued, for I feel a complete knowl- 

 edge of this interesting subject can be obtained. 



Mr. Edwin A. Stevens^ Jr., Member: — -I wish to second Mr. Gardner's remarks and 

 words of congratulation to Professor Everett. As there is one point that was not mentioned, 

 I thought it might be well to say something about it, although I hesitate to speak after such 

 a prominent naval architect as Mr. Gardner. About fifteen years ago I had quite some expe- 

 rience in sailing yachts known as the scow type, short water-lines and long, flat ends. This 

 type of boat needs a sail with more draft than the deeper type of yacht, such as are being 

 built now under the universal rule. Not only is more draft needed, but they cannot be sailed 

 as close to the wind, with good results, as deeper bodied boats. It is necessary to ease off 

 the sheets and to make up by footing what you lose in pointing. I have tried trimming the 

 sails flat and pointing up with the deeper bodied boat, and fell hopelessly behind. The minute 

 I eased up on the sheets and pointed off, in some cases as much as a point (especially in 

 light weather, where there is quite a sea), she would make up in footing what I lost in 

 pointing. 



The President: — Is anyone else prepared to discuss the paper? If not, the Secretary 

 has some communicated discussion which he will present. 



