1. TOWFISH DRIVER

2. Towfish
The towfish is used to localized à towed sensor without USBL posit, sidescan sonar, magnetometer…..
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.
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.

3. 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

4. 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.

5. Setting up a Towfish Driver
In Hardware, add the driver to position your main vessel
GPS.DLL in this example.
Create a 2 mobile for your towfish position.
Named ‘Sidescan’ in this example.
Select a driver to position the towfish.
Towfish.DLL
Select Sidescan Survey in System (check Include box for Sidescan Survey)
Changed cablecnt.dll to towcable.dll. Towcable is a later dll and more accurate to reality.
Note:
If you are towing a sidescan, you need to create the mobile in Hardware before selecting the sidescan option

6. Configuration Sample
Configuration with a sidescan sonar and Magnetometer.

7. Connection Block Diagram With SS
Your computer
HYPACK
SURVEY
Mobile position
POSITION, HEADING
MEMORY
SHARED
Sensor Altitude
Depth value
SIDE SCAN
SURVEY
Hypack Mobile
Pulley
GPS
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.

8. Set up Catenary factor value ie
Cable out input source Layback Method calculation Number of segment Pulley’s Offset in Boat referential. Record method if connection with the pulley is lost
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.
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

9. Set up
DO NOT USE GENERIC OFFSET.

10. Layback method calculation: HYPACK

11. Layback method calculation T. Backer

12. Layback method calculation: SHOM

13. 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.

14. 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.

15. Layback method calculation: SHOM
Specific Method is equivalent to Classic Method.
This method is more adapted:
when the pulley Z offset is important.
When the surveyor want to do the zero pulley at the surface.
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.

16. Layback method calculation: SHOM
If (I+z)²>(k.L) then an alarm is displayed in real time.

17. Cable out input Method
Several counting pulley could provide automatically the cable out information via a serial connection or shared memory.

18. The towfish’s immersion for Sidescan.
Two possibilities:
Depth sensor on fish, then select Sidescan interface and Depth Sensor.
There is no Depth Sensor on the sidescan then the immersion is approximate calculation.
SS Depth=Boat Depth- SS Altitude

19. 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

20. Towfish Survey Window Display Tab
Display all the different information

21. Towfish Survey Window
Cable Out and altitude graph

22. Towfish Survey Window
Visual Graph

23. Towfish Survey Window
Variables Display

24. 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.

25. 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.

26. 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

27. 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

28. 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.