1873.] in determining the best Course for a Ship. 265 

 From the materials contained in Tables I. and II. we have to calcu- 



Fig. 1. 







\ ! 



4 Jioints o£f w 



w.d 





'/[■ 



^ — — — 







[ %k -. ■ 





-ffm. 





- - S \ 





1 



1 i 







J 











° \ 

 \ 



V: : 



2yj J 







\ 











$0 



16 



Jsoehrojie of .Beau, 



fart iS9iifi 





late the average distance towards each of the 4 cardinal points that the 

 ship is capable of accomplishing in a day. 



The ship that on each of the 100 occasions makes the best of her way 

 to the N. experiences the following weather. The wind is right ahead of 

 her (that is, is N.) on 30 occasions, with an average force of 3 ; therefore, 

 under those circumstances, as we learn from Table II., she will sail an 

 aggregate distance of 30 X 24=720 miles. On 25 occasions the wind is 

 abeam (E.) of her, with a force of 2, and she sails under these conditions 

 25x38=950 miles; on 15 occasions it is astern (S.), with force 1, by 

 which she makes 15x12=180 miles ; and, lastly, it is abeam (W.) on 

 10 occasions, with force 2, contributing 380 miles. Therefore the total 

 distance she would sail in the 100 voyages, each of one day's duration, 

 and in every case to the N., is 720 + 950 + 180 + 380=2230 miles ; and 

 consequently her average daily performance to that point of the compass 

 is 22-30 miles. 



Similar computations give 34-40 for an E. course, 37 - 75 for a S., and 

 38-00 for one to the W. The form of calculation is appended in 

 Table III. 



If we take a point A, fig. 2, and mark from 

 it the distances we have just obtained, and draw 

 a contour, with a free hand, enclosing the dots, 

 we shall have a figure such as is represented, 

 which determines the performance of the ship 

 from A to every point of the compass. It should 

 be borne in mind that, although there must be 

 much guess work in drawing the curve under 

 the guidance of only 4 dots, there will be con- 

 siderably less chance of error when we have 8, and none of appreciable 



Eig. 2. 



i /^v 



-=j — > 





1 \ 





' \ 



i \ 



V' 





- / i 





















