14 AERODYNAMICAL EXPERIMENTS UPON A YACHT'S MAINSAIL. 



the drive or speed of the boat, while scientifically correct, are misleading, if he looks at them 

 from a practical point only. Of course, with the wind say 15 miles an hour, the speed of 

 the boat must be added or deducted from this figure in estimating the real force of the 

 wind, so that the speed of the boat would be quite different from those outlined in Professor 

 Everett's experiment — that is, as the layman sees it. 



In actual practice, I once made some quite elaborate experiments and found that on a 

 21-foot boat the greatest speed was at some six points off the wind. Some time I will show 

 the author the relative speeds on all the different points of sailing as I found them in these 

 experiments. 



I hope that he will have continued opportunity to keep on with these sail experiments 

 and will be willing to let me know what he is doing in regard to them. There are many prac- 

 tical questions which experience has suggested to me as being worthy of scientific experimen- 

 tation, and I would like to feel that somebody was working them out. 



Mr. Guy Lowell (Communicated) : — I was most interested in the paper on wind tun- 

 nel experiments with the model of a sail, and am sure that the Society of Naval Architects 

 will, too, find it very interesting when it is presented next week. I received the paper on my 

 return to Boston yesterday, and, therefore, can only give a hasty impression of it ; I have had 

 no time to compare Professor Everett's results with those of others. 



As I wrote the author last fall, I have given a good deal of study to the subject, and the 

 most difficult part has been to determine : 



1. What problems we needed to solve aerodynamically in order to study sails. 



2. What results had already been obtained by wind tunnel workers. 



3. In what way we have had a right to apply the experimental results in a general way 

 to sails. 



Since these three questions have been much in my mind during my studies, I must be for- 

 given if I apply them in reading this paper, and then give my opinion about it. 



In the first place, I do not think sufficient emphasis is laid in the paper on the really valu- 

 able facts contributed by the author (such as the value of P, at top of page 5, and its relation 

 to Eiffel's surface with a camber of 1/7), and that, per contra, too much stress is laid on cer- 

 tain deductions the author seems to have no right to make, or, to be fairer, has no right to 

 lead his reader to make, because in order to simplify his explanations and calculations he quite 

 rightly eliminates certain very real factors ; but in applying the results of his experiments to 

 real sailing conditions he in turn neglected to put back those qualifying factors. For instance, 

 the yachtsman knows by experience that the paragraph on page 5, beginning with the sentence, 

 "It is interesting to consider on what direction of sailing the boat is driven the fastest by 

 this sail," is not true. 



This is because in actual sailing, such as the author assumes when he makes a practical 

 application of his data to the sailing of a ship, there can be no such thing as a constant apparent 

 wind, which he appears to assume as a condition of his practical problem, for though the real 

 wind is constant in wind tunnel experiments, and may even be assumed to be so on the open 

 water, there is no such thing conceivable as a constant speed of apparent wind when the direc- 

 tion of the course of the boat, and therefore its speed, in relation to a steady real wind, is 

 varying. I enclose the following solution, using Professor Everett's resultant, which shows 

 that a boat can sail faster with wind abeam than with wind aft, as his figures imply. 



