Specifications

BATS AND PORTABLE BATS INSTALLATION

2-50

2.4.2 HYDROPHONE X AND Y OFFSETS AND HYDROPHONE DEPTH

Hydrophone Offsets are used to reference the target position to the pitch / roll center of the vessel

and also to correct for the hydrophones dynamic motion. Hydrophone motion is due to the pitching

and rolling of the vessel when it is not on the pitch or roll center of the vessel. ( It is assumed the

hydrophone is rigidly mounted to the vessel. ) The hydrophone, when mounted offset from the

vessel’s pitch / roll center, swings in an arc about the pitch / roll center causing variations in the

hydrophone depth, X and Y offsets as the vessel experiences dynamic motion. These variations

cause the target to appear at a different depth, depression angle and bearing than it actually is.

By entering in X, Y and Z offsets the system can correct for this dynamic motion if a survey grade

Motion Sensing System is interfaced to the BATS. See EdgeTech Model 4414B Motion Sensing Sys-

tem. Connect the analog outputs from the Motion Sensor to the rear panel Gyro/VRU input con-

nector.

Hydrophone X and Y offsets are entered with respect to the pitch / roll center of the vessel. ( It is

assumed that the vertical reference for the pitch / roll center is the water-line of the vessel or the

entered “DEPTH OFFSET”. )

NOTE: The Trackman Software outputs the target position (X & Y) with respect to the pitch

/ roll center of the vessel graphically in the Display, numerically in the Status Block

and also on the RS-232 serial communications port.

In Figure 2-26, horizontal distance and bearing (X & Y) for the beacon are determined relative to

the pitch / roll center of the vessel (C). (Note that the slant range remains relative to the Hydro-

phone.) Determine the Hydrophone X and Y offsets as follows:

A. Measure the distance between the hydrophone (H) and the pitch / roll center of the vessel

The X coordinate is the distance perpendicular to the centerline (dx

in Figure 2-27). The Y

coordinate is the distance parallel to or along the centerline (dy

in Figure 2-27).

Distance along the X-axis from the centerline towards a starboard direction has a positive

value. In this example, the X offset is 7 meters. Distance towards the port side of the ves-

sel has a negative value.

The hydrophone's distance along the Y-axis, forward of the pitch / roll center, is a positive

value. In Figure 2-27, the hydrophone is aft of the pitch / roll center, and the Y offset is -10

meters.

B. Enter the offsets at the Trackman and observe the display to verify that the hydrophone is

being offset in the proper directions. Figure 2-27 illustrates the tracking window display as

the X and Y offsets determined above are entered.