TOWFISH DRIVER
Towfish

The towfish is used to localized à towed sensor without USBL posit,
sidescan sonar, magnetometer…..
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The towfish driver allows an accuracy estimated position of the
mobile by merging different information and filtering navigation of
the boat.

In a hardware configuration several mobile could be create, a
Towfish driver could be associate to each mobile.
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If two mobiles are created, the sidescan sonar mobile should be the
first in the configuration, the shared memory root the first mobile
position to the Sidescan survey program.
Towfish: Merge Information
Horizontal distance
A-Frame Offset
Layback Calculated
Z Offset
Cable out x Catenary factor
Depth
Depth Boat
Altitude
Towfish driver setting
Sidescan Survey Information
Survey Information
Towfish Driver Calculation
Towfish: Filter and smooth Boat navigation
In real time the driver makes a
calculation of the mobile position by
applying filter and latency on the
boat heading.
The estimated calculation of the
mobile is close the reality.
Setting up a Towfish Driver

In Hardware, add the
driver to position your
main vessel


Create a 2 mobile for your
towfish position.


Named ‘Sidescan’ in this
example.
Select a driver to position
the towfish.


GPS.DLL in this example.
Towfish.DLL
Select Sidescan Survey in
System (check Include box
for Sidescan Survey)
Note:
If you are towing a sidescan, you need to create the mobile in
Hardware before selecting the sidescan option
Configuration Sample
Configuration with a sidescan sonar and Magnetometer.
Connection Block Diagram With SS
Your computer
Mobile position
HYPACK
SURVEY
Pulley
GPS
POSITION, HEADING
MEMORY
SHARED
Sensor Altitude
Depth value
Hypack Mobile
SIDE SCAN
SURVEY
Side Scan Sonar

Towfish driver calculated in Real Time the position of the mobile.

Information is passed between the two modules using the shared memory.
Set up
Cable out input source
Layback Method
calculation
Catenary factor value ie
K=0.9 pour 100m cable out the
cable out value calculated is 90m.
Depth Source if advanced formula
is used for calculation.
Number of segment
Pulley’s Offset in Boat
referential.
If Depth Source= Fish Depth use
to select the Depth value:
-Shallow fish: fish at the surface
-Deep fish: deep under the boat
-Depth Sensor/Altitude Sensor
coming from the selected channel
Record method if
connection with the
pulley is lost
Set up
DO NOT USE GENERIC OFFSET.
Layback method calculation: HYPACK
Layback method calculation T. Backer
Layback method calculation: SHOM
Layback method calculation : SHOM
Basic Method :
Do not apply Pythagoras Calculation only the
multiplication of the catenary factor and the
cable out.
The result will be the Layback.
Layback method calculation : SHOM
Classic Method.
Pythagoras with values coming from.
Hardware:
•Catenary factor,
•Z pulley.
Survey
•Cable Out.
Sidescan Survey
•Sensor immersion
•Boat Depth –Altitude or Depth sensor
For a good calculation:
• Zero pressure sensor should be done on subsurface.
• Zero Pulley should be done at the pulley.
• If (I+z)²>(k.L) then an alarm is displayed in real time.
Layback method calculation: SHOM
Specific Method is equivalent to Classic
Method.
This method is more adapted:
• when the pulley Z offset is important.
•
For a good calculation:
• Zero pressure sensor should be done on subsurface.
• Zero Pulley should be done on subsurface.
• If (I+z)²>(k.L) then an alarm is displayed in real time.
When the surveyor want to do the zero
pulley at the surface.
Layback method calculation: SHOM
If (I+z)²>(k.L) then an alarm is displayed in real time.
Cable out input Method
Several counting pulley could provide
automatically the cable out information
via a serial connection or shared
memory.
The towfish’s immersion for Sidescan.
Two possibilities:
1.Depth sensor on fish, then select
Sidescan interface and Depth Sensor.
2.There is no Depth Sensor on the
sidescan then the immersion is
approximate calculation.
SS Depth=Boat Depth- SS Altitude
The towfish’s immersion for other sensor
Some towed sensor as Magnetometer
could provide depth information.
Depth Source:
•Enable Mobile Depth
Fish Depth
•Enable Depth Sensor
Fish Depth Channel
•Select the input Channel
Towfish Survey Window
Display Tab
Display all the different
information
Towfish Survey Window
Cable Out and
altitude graph
Towfish Survey Window
Visual Graph
Towfish Survey Window
Variables Display
Cable out Manual Input
In Manual Mode, cable out could be set by:
•Using arrow
•Input in the dialog box
The Cable out Adjustment:
If a counting pulley is using the cable could slide on the
sheave, if cable mark has been done then surveyor could
adjust the cable out value.
How improve the estimated position
1-mark you cable (10m,15m,20m..) to control the information delivered
by the pulley.
2-when you put back the fish on boat check the coherence of the zero
pulley you did when you put the towfisn in the water.
3-If it is a long survey it could interesting during the day to do again the
zero pulley.
These actions will improve the estimated position of the fish, note that a
transvers current could decrease the position.
Calculated the Catenary Factor for SS
1-Do the same line in the two ways on a remarquable obstruction.
2-In Hyscan make a target on these obstructions for each line
3-Measure the distance between the two targets divide per 2 or the
average of the distance between the obstruction and the target,
It is the Error E
Calculated the Catenary Factor for SS
4-In Hyscan load the two lines and activate spredsheet
5-Clic on the obstruction the spreadsheet will display the value
Calculated the Catenary Factor for SS
6- Take the information in the spreadsheet.
•Layback Logged is the calculation did by towfish driver
•Cable out (L)
•Depth: sensor immersion (I)
•Pulley Offset (Z) from Hardware
7- Calculate the correct K factor.
The K factor depends of the survey speed and the cable out value.
For the same system the k value could be different for 20 m cable out and 150m cable out.