OPERATIONS AND MEASUREMENTS 



491 



loss, the use of a second experimental vessel carrying 

 the receiver might be eliminated by echo ranging 

 through the wake at a target sphere and measuring 

 the intensity of the echo returned to the transducer. 

 From echo ranging at wakes, usually the wake-laying 

 vessel proceeds at constant speed on a straight course 

 past the measuring vessel, which either may run a 

 parallel course with different speed or may be hove to. 

 Maintenance of prescribed speeds and course de- 

 mands accurate seamanship. The relative positions 

 of the two vessels as a function of the time are de- 

 termined by direct triangulation and dead reckoning. 

 During echo-ranging experiments, an incidental check 

 on those geometric data is obtained by the acoustic 

 ranges. 



During transmission runs, the range from the cruis- 

 ing auxiliary vessel, which carries the projector, to 

 the measuring vessel has been accurately determined 

 by the use of airborne sound; simultaneous radio and 

 sound signals are transmitted from the auxiUary 

 vessel, and the difference between the automatically 

 recorded times of arrival of the two, multiplied by the 

 velocity of sound in air, yields the range. Moreover, 

 for transmission runs, the courses of the operating 

 vessels have to be laid out and maintained with great 

 care in order to avoid interference with the acoustic 

 measurements from the auxiliary vessel's own wake. 



In working with wakes which are laid and then 

 allowed to age before the measurements or while the 

 measurements are being conducted, the exact loca- 

 tion of the wake soon becomes difficult to discern. 

 If the wake-laying vessel lies to, it usually soon drifts 

 enough to be useless as a marker for one end of the 

 wake. The following method has proved helpful when 

 working either with surface craft or submerged sub- 

 marines, particularly with very long wakes. A small 

 boat lies to at a point near where the initial end of the 

 wake will be laid. As the wake-laying vessel goes by, 

 the small boat moves into the center of the wake and 

 releases a small amount of fluorescein ;"■ chrome yel- 

 low or any other nonsoluble dye which floats on the 

 surface is not satisfactory for this purpose, since 

 wind drift can move it away from the wake. In the 

 case of a submarine, it submerges as it passes the 

 small boat or if already at periscope depth, the sub- 

 marine releases the fluorescein. The wake-laying 

 vessel releases fluorescein into the wake at the end of 

 its run. Both this ship and the small boat then keep 



their bows touching the dye spot, thus keeping their 

 net drift the same as that of the wake. More fluores- 

 cein is dropped off the bow of the marker boats at 

 intervals; one marking will not last when working 

 with wakes older than 20 to 30 minutes. If the ob- 

 serving vessel crosses the wake in the course of its 

 measurements, the wake is located by sighting on the 

 marker boats; the use of a simple optical device for 

 lining up the markers is recommended. One of the 

 marker boats takes a stadimeter range on the vessel 

 which crosses the wake; this procedure aids in com- 

 puting the wake age at that point. If successive cross- 

 ings are made, fluorescein is dropped from the ob- 

 serving ship just as it lines up the marker boats. The 

 marker boat closest to this point then moves up to 

 the new dye spot; this insures that the wake between 

 markers remains free of extraneous wakes. Where 

 marker boats are not available, it is helpful to use a 

 mixture of fluorescein and chrome yellow as a marker. 

 The two colors drift apart if any wind is present; the 

 chrome yellow can be seen farther away and is used 

 to locate the fluorescein. 



30.2.1 



Training Errors 



" Before using fluorescein in experiments at sea, it should be 

 ascertained whether special authorization by the Area Com- 

 mander is required. 



In echo ranging on wakes the trainable transducec. 

 is usually operated at a fixed relative bearing. How- 

 ever, in measuring the transmission loss across a 

 wake, it is necessary to keep the trainable projector 

 of the sending vessel aimed at the hydrophone of the 

 receiving vessel; continual changing of the bearing of 

 the transducer is also necessary in echo ranging 

 through the wake at a target sphere. For this purpose, 

 an observer is stationed on the flying bridge to oper- 

 ate a repeating pelorus, to be aimed at the auxiliary 

 vessel or target sphere. A second man stationed at the 

 control stack matches the projector-heading indi- 

 cating "bug" to the target-bearing repeater. Even so, 

 the projector heading does not hold precisely to the 

 true target bearing. The deviation is partly attributa- 

 ble to the lag in the various linkages of the system and 

 partly to the impossibility of holding the pelorus ac- 

 curately on the target at all times. Under practical 

 conditions as prevailing on board the USS Jasper 

 (PYcl3), the estimated errors and their sources are as 

 follows: ' (1) pelorus aiming error +2 degrees in fair 

 weather; (2) control stack matching error, projector 

 bearing to target bearing + 2 degrees; (3) lag in train- 

 ing system, gears and projector-heading repeater 

 system +2 degrees maximum prior to April 1944, 

 when the system was overhauled a^jd the error re- 



