Edgetech USBL BROADBAND ACOUSTIC TRACKING SYSTEM, User Hardware Manual, Page: 63 / 102

3-17
Hydrophone Offsets
The BATS computes range and bearing relative to the hydrophone, unless the system is instructed to add
or subtract corrections (offsets) which relate range and bearing to some other reference point on the
vessel. The hydrophone centerline, or zero bearing, is indicated by the index mark, shown in
F
IGURE
3-3
and F
IGURE
3-4 , and is generally aligned so that it corresponds to the vessel heading.
It is difficult and time consuming to fabricate a mounting in which the hydrophone heading is aligned
within a degree of the vessel centerline, unless the vessel is in a drydock. If you have the facilities to
perform an exact mechanical alignment or if the installation is to be permanent, consider fabricating a
mount that repeatedly returns the hydrophone to the same physical location aligned to within 0.5° of the
vessel centerline.
Most operations requiring a Portable BATS will be on various vessels of opportunity, and require quick
and temporary mounting. The Desktop/Rackmount systems offer a more permanent solution. In this case
align the hydrophone with the vessel centerline as closely as possible. Use some variation of the following
procedure to determine hydrophone offsets.
3.3.1 Hydrophone Bearing Offset
The bearing offset must be determined before X, Y, and Z offsets can be measured.
1. Measure distance (d) from vessel centerline to the hydrophone location as shown in F
IGURE
3-13 .
NOTE:
Most vessels have a centerline weld or plank running down the
deck that can be used for alignment purposes. If in a seamless deck
vessel, measure the vessel beam and determine the true centerline.
2.
Weight a line to suspend the acoustic tracking source vertically in the water.
3. As far forward on the vessel as possible, hang the weighted acoustic beacon over the side at the
same distance from the vessel centerline as the hydrophone, position B1 in
F
IGURE
3-13 . It may be
necessary to use a length of pipe or a boathook to extend the weighted line the required distance.
The beacon should be slightly deeper than the hydrophone.
4. Turn the System on and set it up to track the beacon in use. If you have aligned the mounting
bracket correctly, the system tracks the beacon at or very near a 0.0° bearing.
5. If you have designed a mounting that can rotate while in the vertical position, you can rotate the
hydrophone until you obtain the correct reading. If you cannot rotate the pipe it will be necessary
to enter a bearing correction at the time of operation. Bearing Offset can be entered under the
USBL HYDROPHONE PARAMETER menu.