150 HYDROGRAPHICAL SURVEYING [chap. v. 



The proper positions for the floating beacon and the ship 

 require careful consideration to obtain the best results. E is 

 a floating beacon, with bamboo 30 feet high and large black 

 flag, well moored and placed off the coast in such a position 

 as to satisfy as nearly as possible the following conditions : 



(a) As near the coast as possible consistently with being 



visible from C. 

 (6) Within visual range of C (7 miles is usually a safe 



distance). 



(c) In such a direction from B as to form approximately 



an isosceles triangle whose apex is the first position 

 of the ship at F ; bisecting the angle A B F will be 

 a guide to this direction. 



(d) At as great a distance from B as is consistent with 



obtaining a sufficiently large receiving angle between 

 A and B. 



Fig. 38. 



F is the first position of the ship, moored taut without the 

 ST\avel, and taken up with a view to making each of the re- 

 ceiving angles B F E, E C F sufficiently large ; neither should 

 be less than 30°. Z E C F is roughly known by the difference 

 in the bearings of C from E and F. 



G is the second position of the ship, situated as near the 

 coast as possible consistently with both C and D being dis- 

 tinctly visible, and the receiving angle B G C not greater than 

 120° or 130°, whilst keeping the receiving angle E G B as large 

 as possible. 



H is the third position of the ship, in a direction from C 



