2722 



HYDROGRAPHIC MANUAL 



Page 156 



2722. Forty-Foot Signal 



The type of construction of the 98-foot signal can be used to build hydrographic signals of various 

 heights. The 16-foot base section is identical and the signal may be built up in sections to the ele- 

 vation desired. For a 40-foot signal, guys are fastened at the 25- and 40-foot levels The target 

 may be similar to that of the taller signal. If desired, one corner instead of a side of the scaffold 

 may be pointed seaward. In such a case, the target boards are cut in 8-foot lengths and nailed on two 

 sides to form a V whose apex points seaward. 



Numerous types of signals can be built up to heights of 40 feet. The choice depends mainly on 

 the quantity of lumber available, especially if there are no roads for transportation and all materials 

 have to be landed from the ship. Pole signals constructed of 2 by 4's, in cross sections of 4 by 4 inches 

 or 4 by 6 inches, with targets made from J^^- by 6-inch boards, have been erected 40 to 60 feet high. 

 Tripods 40 feet high have been erected, but generally lumber in lengths longer than 16 feet is required 

 for the horizontal braces at the base. If native trees are available, pole tripod signals can be 

 constructed. The various types of tripods can be dressed with whitewash, painted boards, canvas, 

 or signal cloth. 



2723. Ordinary Tripod Signal 



The ordinary tripod signal usually serves a dual purpose. It serves as a triangula- 

 tion signal, being constructed in such a manner that an observer can set up his theodolite 

 under the tripod and make observations without moving any of the structure. And 

 it makes an ideal signal for inshore hydrography at distances of 3 to 5 miles, and even 

 farther, if the elevation of the ground is sufficient and the tripod is properly dressed. 

 (See fig. 43.) 



SCALE IN FEET 



Figure 43.— Tripod signals. 



