4462 HYDROGRAPHIC MANUAL PagE 354 



of wire payed out will measure the true distance and be so indicated on the revokition 

 counter, if it has been properly calibrated. 



4462. Small Taut-Wire Apparatus 



The small taut-wire apparatus operates on essentially the same principle as the large apparatus but it is built in one compact 

 unit that is very similar in appearance to a wire sounding machine. On each side of a sheet-metal base, IVA inches wide by 35 inches 

 long, are welded triangular-shaped supports, 21 H inches high, for a spindle, on which a reel with a capacity of 20 miles of piano wire 

 is permanently moimted. A brake drum, fixed on the spindle, is partly surrounded by a band brake operated by a wheel 

 momited near the top of one of the triangular-shaped supports. A horizontal bar, pivoted above the center of the reel, has a cyclom- 

 eter wheel geared to a dial-type of distance indicator on the after end and a spring balance on the forward end. This assembly 

 forms a beam-type of dynamometer to measure the tension on the wire. 



The distance is registered on a round dial having two concentric graduated scales each of which has a clock-like pointer hand. 

 The inner scale is divided into 20 nautical miles, subdivided in tenths of miles. One revolution of the outer scale is equivalent to 

 0.2 nautical mile, divided and marked in hundredths of a mile and subdivided in thousandths, so that distances may be estimated 

 to ten-thousandths of a nautical mile. An attachment is provided so that both pointer hands may be set at zero or as desired. 



The lower end of the spring balance is attached by a metal rod to the base, and its upper end is suspended from the forward end 

 of the horizontal bar. From the spring balance the tension on the wire may be read to half-pounds on a circular dial graduated from 

 to 100. When the apparatus is in operation the brake should be adjusted so that a tension of 36 to 40 pounds is indicated on the 

 spring balance. 



The apparatus should be installed and cared for and distances should be measured with it in much the same manner as described 

 for the large taut-wire apparatus (see 4463, 4464, ajid 4466). The operation of the apparatus is slightly different, for the reel revolves 

 as the wire is payed out instead of remaining stationary as it does on the large taut-wire apparatus. Depending on the freedom with 

 which the reel revolves, a heavier anchor may be required than is used with the large taut-wire apparatus. 



The apparatus is prepared for use by reeving the wire from the bottom of the reel over the after side of the cyclometer wheel and 

 three-quarters of a turn around it. The wire crosses below the cyclometer wheel, and is then passed under the fair-lead sheave on 

 an arm attached to the after end of the base. From here the wire is lead over the stern of the vessel, through fair-lead rollers if 

 necessary, and the anchor weight attached as explained in 4465. 



The reel is not removable and the wire must be wound on it on board ship. The wire should be wound on the reel under ten- 

 sion. It should be led from aft around the cyclometer wheel and under the fail-lead sheave on to the bottom of the reel. A manually 

 operated attachment is provided at the base of the apparatus for use in winding the wire in even layers. A rope pully is attached to 

 one end of the spindle so that power may be used and a crank is supplied for use in turning the reel by hand power. 



There is insufficient clearance where the wire crosses imder the cyclometer wheel; the wire coming off one side of the reel clears 

 but will rub coming off the other side. Wire in one continuous piece should be used, but where splices are necessary they must be 

 made securely and neatly, and they should be wound on that side of the reel where they will pass through the apparatus without 

 interference. 



The apparatus should be calibrated in the manner and with the accuracy de- 

 scribed in 4467 for the large taut-wire apparatus. The instrument may be read to 

 closer limits, however, and a measured mile course marked by shore ranges should be 

 of sufficient length to determine an accurate calibration factor. 



4463. Installation of Taut-W ire Apparatus 



The taut-wire apparatus must be installed near the ship's stern, and preferably where the wire, as it leaves the after rollers, will 

 lead fair over the stern into the water. Such an installation is often impracticable, for the weight of the apparatus confines it to the 

 main deck and the height of the taffrail often requires additional rollers to lead the wire over it astern. The two parts of the large taut- 

 wire apparatus should be alined parallel to the centerline of the ship. There must be sufficient clear space between the standard and 

 the measuring-apparatus stand for the flyer to revolve without interference, and a clear space aft of the apparatus for the wire to pass 

 over the stern. A suitable location may generally be found on tlie quarterdeck or in one of the deck passageways between the house 

 and the bulwarks. In the latter case, if there is a choice of sides, that side should be preferred where the revolution counter can be read 

 most conveniently. 



The standard and reel full of wire weigh approximately 3,000 pounds, so the standard must be mounted on a substantial foun- 

 dation. The standard on a wooden base is bolted to the deck with H4-inch through bolts, engaging a structural member of the ship's 

 hull. The axis of the reel must be parallel with the centerline of the ship. A special davit is furnished with the apparatus, to be 

 mounted near the standard for use in handling the heavy reel, but it may not be required if the standard is located where a boat 

 davit can be used instead. 



The measuring-apparatus stand should be installed with its forward end not less than 13 feet astern of the standard (fig. 75). It 

 must be installed so that it will be level when the ship is trimmed normally and on an even keel for the dynamometer to function 

 properly. If the dynamometer is inclined, the frame will bind on the guide rods, restricting its vertical movement and preventing 

 the registration of the true tension of the wire. The stand is generally fastened by bolts through the deck and mounted on thwart- 

 ship blocks which are wedged on the outboard side, if necessary, to make the installation level. 



If additional rollers are required on the stern they are generally improvised from material on board. They may be either per- 

 manently secured to the taffrail or mounted on a suitable piece of lumber to be lashed securely to the rail when in use. 



