|
A plotting board was a mechanical device used by the U.S. Coast Artillery to track the observed course of a target (typically a moving ship), project its future position, and derive the uncorrected data〔Before firing, the uncorrected firing data from the plotting board were corrected to account for such factors as the current weather, the level of the tide, the batch of powder being used by the guns, and/or were adjusted based on observations from spotters who reported on the fall of earlier shots at the same target. For details, see corrected firing data.〕 on azimuth (or direction) and range needed to direct the fire of the guns of a battery to hit that target. Plotting boards of this sort were first employed by the Coast Artillery〔Other types of plotting boards, used for the ''field artillery'', are not described here.〕 around 1905, and were the primary means of calculating firing data until WW2.〔Towards the end of WW2 these boards were largely replaced by radar and electro-mechanical gun data computers, and were relegated to a back-up role.〕 Although several different types of plotting boards were used by the Coast Artillery over the years, the example described here is the Whistler-Hearn Plotting Board, Model of 1904 which was widely employed by the Coast Artillery between about 1905 and 1925.〔Other boards included the Cloke plotting and relocating board and the so-called 110 Degree plotting board. For a summary see "Coast Artillery Plotting Boards 1904-1945" by Fredrick M. Baldwin, in "American Seacoast Defenses: A Reference Guide," Mark A. Berhow, Ed., CDSG Press, McLean, VA, 2004〕 This description is primarily derived from two manuals of the period, each of which leaves certain aspects of the board's design and use unexplained.〔"The Service of Coast Artillery," Frank T. Hines and Franklin W. Ward, Goodenough & Woglom Co., New York, 1910, p. 315 ff. Plates XXV and XXVI on this page are from this source.〕〔"Training Manual No. 1669: Description of the Whistler-Hearn Plotting Board (Model of 1904), Mortar Plotting Board (Model of 1906 and Model of 1906 MI), and Submarine Plotting Board (Model of 1906) and Instructions for Assembling, Adjusting, Caring the, Etc.," Ordnance Department, U.S. Army, Government Printing Office, Washington, April 24, 1907, Revised December 13, 1909. This source contains engineering quality drawings of the board's mechanisms, including plans and elevations, but these are incompletely annotated.〕 A 1940 manual also describes the Whistler-Hearn board.〔"FM 4-15 Coast Artillery Field Manual-Seacoast Artillery Fire Control and Position Finding," U.S. War Department, Government Printing Office, Washington, 1940, p. 84ff.〕 ==Overview== The Whistler-Hearn plotting board〔It has been about 90 years since the Whistler-Hearn plotting board was widely used, and the details of its operation must be inferred from manuals and drawings of the period.〕 (see Plate XXV at right, top) was a semicircular wooden table about 7.5 feet in diameter with a mechanism on top that could be configured to represent the geography of the harbor area in which it was used, including the locations of the base end stations that observed targets for the gun battery it controlled and the location of the gun/s of that battery.〔The guns were located with reference to their directing point, the point for which the firing data were calculated. Making the firing data relative to the osition/s of the gun/s was called the relocation of these data. Relocation was part of the analog function of the plotting board and was enabled by adjustments to the gun arm center of the board (see plate and explanation below)〕 The mechanism of radial arms and adjustable slides, arcs, and gears converted observations that had been telephoned in from the base end stations into firing data for the guns〔.〕 The plotting board for a given gun battery was located in the plotting room for that battery (shown at right, bottom), a space often attached to an observation post or protected within a reinforced concrete bunker or casemate. It was served by a large crew (often more than a dozen soldiers) who were part of the Range Section of the battery personnel.〔A thorough overview of how the Coast Artillery fire control process was organized and staffed and how the plotting board was employed is contained in "Gun Battery Organization and Duties I: HQ and Range Sections (1940) in "American Seacoast Defenses: A Reference Guide," Mark A. Berhow, Ed., CDSG Press, McLean, VA, 2004.〕 To locate a target, plotting board operators used two radial arms (called the primary and auxiliary arms), and "locked-in" the ends of these arms along on the notched azimuth scale that ran around the circumference of the board at the azimuths of the sightings that were telephoned in to them by the two base end stations. These locked arms and the baseline arm (along the base of the arc) then formed a triangle whose vertices were the two observation stations and the target. This located the target on the board,〔It should be noted that the target was not located by direct triangulation from the observations of the base end stations, even though the locations of these stations and the distance between them as well as their observing angles to the target were known. Rather it was the plotted position, relative to these stations and the DP, that was computed on the board.〕 and its position was then marked by punching a hole in the paper placed over the plotting board. Next, another radial arm, called the gun arm, was swung over the plotted position of the target, and the resulting range and azimuth for firing were read off the gun arm and an azimuth scale on the gun arm center. These data were corrected or adjusted for some other variables, and telephoned to the gun/s. The figure at left shows the actual relationship between the distant target (at top), the two base end stations (at either end of the baseline), and the directing point of the battery's guns, as reflected onto the plotting board. The triangle formed by the B1 (primary) arm, the B2 (secondary) arm and the base line arm is the small triangle at the base of the plotting board, and the gun arm is shown swung over the intersection of the other two arms in order to read the range and azimuth to the target. Another helpful diagram is shown on the base end station page—the cutaway diagram of a battery's plotting room (with its plotting board), shown next to the two base end stations, and behind the directing point of the battery, between its two guns. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Plotting board」の詳細全文を読む スポンサード リンク
|