hollow brass coil spring which carries a stylus 

 at its free end. The stylus records the move- 

 ments of the Bourdon, as it expands or con- 

 tracts with changes of temperature, on a 

 smoked-glass slide. The temperature range is 

 from 28° to 90° F. 



The slide is held rigidly on the end of a coil 

 spring enclosed in a copper bellows, or sylphon. 

 Water pressure, which increases in proportion 

 to water depth, compresses the sylphon as the 

 BT sinks. This pulls the slide toward the nose 

 of the BT, at right angles to the direction in 

 which the stylus moves, to record temperature. 

 When the BT is raised toward the surface the 

 spring expands the sylphon to its original shape. 

 Thus, the trace scratched on the smoked surface 

 of the slide is a combined record of temperature 

 and pressure, the pressure being proportionate 

 to depth. 



Since external pressure slightly affects the 

 internal pressure of the xylene in the Bourdon, 

 and since temperature changes also influence 

 the movement of the sylphon, each instrument 

 must be carefully calibrated by the manufacturer. 



A special grid is supplied for each instrument 

 for converting the stylus trace to temperature 

 and depth readings. These grids are not inter- 

 changeable between instruments. From an 

 examination of the grid, it will be noted that 

 the temperature lines are not exactly straight 

 and vertical, but curve slightly to the left with 

 increasing depth. Likewise the depth lines are 

 not exactly arcs of circles with radius equal to 

 the length of the stylus, but also allow for 

 thermal expansion of the sylphon. 



At temperatures of 105° F., the recording 

 stylus moves up against a stop pin ; ij this tem- 

 perature is exceeded, permanent deformation oj 

 the brass coil oj the Bourdon will occur, and the 

 calibration of the instrument will be ruined. 

 For this reason, the BT must always be kept 

 out of the sun and away from the vicinity of 

 fire rooms, steam pipes, and other sources of 

 heat. An instrument that has been overheated 

 often may have the stylus arm jammed by the 

 pen-lifter bar in the high temperature position. 

 If another BT is aboard, use it, and turn in the 

 damaged instrument for adjustment. If a spare 

 is not available, gently lift the stylus arm from 

 the pen-lifter bar and let the arm swing back 

 toward the low temperature side. 



The temperature calibration will henceforth 

 be in error as a result of deformation of the 

 Bourdon. 



Record on oceanographic log sheet B that 

 the calibration is uncertain beginning with the 

 next slide, and turn in the instrument at the 



first opportunity. Complete instructions for 

 filling in the log sheet are given in chapter 14. 



2-35 Equipment Needed to Operate the 

 BT.— In addition to the BT itself, the following 

 list of equipment is required to operate the 

 instrument. 



1. A BT winch. BuShips E6/S Hoist, or 

 equivalent, with spares as provided. 



2. A BT Boom. BuShips Drawing 56800- 

 668234. 



3. A BT towing block, counterbalanced, 

 Navy stock No. N 16-600 821-101. 



4. Wire rope, %2-inch diameter 7x7 stainless 

 steel, aircraft control category, in 2,000-foot 

 lengths per reel. 



5. Two grid mount assemblies. 



6. A box of accessories containing: 



a. Four boxes of 50 smoked slides each. 



b. One-half pint can of slide lacquer. 



c. One-half pint can of lacquer thinner. 



d. Two glass dipping jars with tops — one 

 for fresh water, the other for lacquer. 



e. One pair of dipping tongs. 



f. One slide viewer. 



g. One thermometer in a metal case. 



7. One-gallon can of Grade III Rust Preven- 

 tive Compound — Navy Dept. Spec. 52-C-18 

 (Standard Navy Stock No. G52-C-3257-60). 



2-36 Spare Parts Needed for the BT.-^No 

 spares are provided. Those possibly required 

 would be extra smoked slides, lacquer, lacquer 

 thinner, spare reels of wire, and spare towing 

 blocks. 



2-37 Tools Needed To Operate the BT.— 

 The following tools are needed to operate and 

 maintain the BT. 



1. Pliers, 8-inch combination. 



2. Screwdriver, medium. 



3. Adjustable end wrench. 



4. Fifteen-inch round wooden stick. 



5. Rags for cleaning and cooling. 



2-38 Making a BT Lowering.- The BT is 

 designed for lowering from a ship underway at 

 speeds up to 18 knots. Best results, however, 

 are obtained when the speed is not in excess of 

 12 knots. At higher speeds, unless the sea is 

 very smooth, only an experienced operator 

 should attempt to operate the winch. New 

 operators should practice lowerings and recov- 

 eries with a dummy BT before undertaking the 

 operation of an actual instrument. Operation 

 of the BT winch cannot be learned from read- 

 ing a description only, any more readily than 

 one can learn to pitch a baseball or bowl 300 by 

 reading a manual. Nevertheless, the essential 

 steps together with some useful hints are out- 

 lined below. 



18 



H. O. 607 



