Survey of Oyster Bars, Somerset County, Md. ^j 



the corners have been dragged or otherwise moved from their correct positions, and the 

 other, to relocate or reestablish a buoy at the point from which it was removed. The 

 different ways of solving these two problems partly depend upon the instruments 

 possessed by the engineer and his assistants and partly on his training and experience. 



(i) Triangula I ion. — This method is the one that will give the greatest accuracy, 

 but on account of its requiring special data and instruments, and being an operation 

 rarelv used by engineers not engaged in geodetic surveying, it is recommended only for 

 cases in dispute that can not be settled satisfactorily by some other method. An 

 explanation of this class of work would be too long for a report of this sort, and those 

 not familiar with this method are referred to the publications on the subject by the 

 Coast and Geodetic Survey. 



(2) Hydrographic. — This method is the most simple and satisfactory one that can 

 be adopted if the survevor can obtain the use of the necessary instruments and assistants. 

 It is the one best suited for the work of the engineers of the Commission in relocating 

 corners of boundaries, as it gives results of the accuracy ordinarily required and is rapid 

 in execution. Besides, it has the advantage of being available whenever three triangu- 

 lation stations of suitable relative positions are visible from the offshore points needing 

 relocation. 



Most navigators and others familiar with the use of a sextant are well acquainted 

 with the graphic three-point method of fixing a position on water, and only a brief 

 description of the operation will be stated. 



In the case where there is only one engineer, having a single sextant, the three-point 

 method can be used, but not until the two angles determining the position of any buoy 

 have been derived from the "Forward bearing" given in the tabular forms describing 

 the boundaries of the oyster bars. For example, take "Turtle Egg Island" bar, which 

 is the first one described in this publication, and assume that "Corner No. 3," is to be 

 examined as to its position. The angle between the two landmarks "Senator" and 

 "Deal Island Church" as determined from right to left from the forward bearings from 

 this corner is 128 39' and the angle between "Deal Island Church" and "Crab" is 

 99 30'. Having these two angles, the engineer proceeds to the buoy of doubtful location 

 and measures the actual sextant angles between the landmarks for which the calcula- 

 tions were made. If the measured and calculated angles do not agree the buoy is not 

 in its correct position and the boundarv corner must be relocated. This is accom- 

 plished by moving the boat about until a point is reached where angles do agree, and 

 this point being the desired location, the buoy can be placed in its correct position. 



If the engineer can obtain the use of both a sextant and a three-arm protractor 

 ("position finder"), the availabilitv of the hydrographic method is increased, as the use 

 of the protractor is essential in case of the washing away or destruction of one or more 

 of the landmarks originally used in describing the boundaries. Under these circum- 

 stances, any three landmarks of suitable relative positions that are visible from the 

 point to be located can be utilized. For example, the engineer can proceed to the buoy 

 of doubtful position and measure the two adjacent sextant angles between the three 

 landmarks selected. These two angles are set off on the three-arm protractor and the 

 actual position of the buoy plotted on the chart by shifting the protractor about until 

 the edge of each of the three arms passes through the center of the symbols on the 



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