3. EQUIPMENT AND INSTRUMENTS 



89 



Figure 29. — Interior of hydrographic launch show- 

 ing arrangement of equipment. 



tors and batteries are charged at night 

 aboard the vessel. Experience has shown 

 that it is best to charge one battery while 

 operating from the other. It is possible to 

 operate from a battery under charge but 

 precautions must be taken to prevent surges 

 of excessive voltage. A 40 to 50 ampere gen- 

 erator is adequate and a 12-volt automobile 

 generator equipped with a regulator will 

 keep the batteries charged over long periods 

 of operation. If other equipment, such as a 

 radio^ is operated from the same batteries, 

 a larger generator may be required. 



For EDO 255 installations, the 12-volt 

 D.C. system is fed to a converter or transis- 

 tor power supply which in turn provides 115 

 volt, 57.5 to 62.5 cycle A.C. required by the 

 instrument. The Kato rotary converter has 

 been used with satisfactory results but ef- 

 forts are being made to replace it with a 

 transistor power supply which is much more 

 efficient. It is often feasible to place the 

 Kato converter in another compartment and 

 use an extended shaft to operate the fre- 

 quency adjustment knob. A small variac in 

 the A.C. power line to the depth recorder 

 can be used to adjust A.C. voltage as the 

 batteries run down. The battery leads to the 



converter should be as short as practicable. 

 It is desirable to have a 0-15 volt D.C. meter 

 across the battery being used and a 0-150 

 volt A.C. meter across the variac when one 

 is used. 



The transducer can be mounted through 

 the hull or attached to the keel. A fairwater 

 must be built around it to reduce turbulence 

 to a minimum. The transducer is usually 

 located nearly amidships, but no fixed rule 

 can be given. It should not be mounted 

 under the engine, or so far forward that dis- 

 turbed water washes around it at operating 

 speeds, and should not be aft of intake and 

 discharge ports. 



3-109 Bar check apparatus. — The bar 



check is a method whereby the accuracy of 

 an echo sounding instrument may be veri- 

 fied. By using the bar check, the index of an 

 echo-sounding instrument operated at a con- 

 stant velocity may be adjusted to compensate 

 for the draft of the acoustic unit and the 

 instrumental error without knowledge of 

 their amounts ; and when accurate bar checks 

 can be obtained through the full range of 

 depths in the project area, compensation may 

 be made for a velocity of sound differing 

 from the calibration velocity of the instru- 

 ment (see 5-115). 



The bar may be any reflecting surface 

 which may be lowered to a known depth be- 

 low the transducer. Various types of bars 

 have been used, such as a section of 2- to 3- 

 inch pipe sealed at both ends, a section of 

 sheet steel about 9 inches wide and 3 feet 

 long, and a weighted board. One of the most 

 satisfactory bars is one made of 6 to 8 sec- 

 tions of thin walled tubing, such as con- 

 denser tubes. The ends of the tubes are 

 plugged and made water tight. The tubes 

 are placed about '/i-inch apart and clamped 

 in position with 3 sections of strap iron, and 

 a hinged yoke is secured to each end of the 

 bar. Additional weight is required to over- 

 come the bouyancy of the trapped air and 

 keep the suspending lines taut. The overall 

 length of the bar should be approximately 

 equal to the beam of the sounding launch. 

 If the bar is to be u.sed in depths greater 



