Other Interest > DIY - Side Scan Sonar and towfish

DYI towfish Mminnesota

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Following the great information in this forum, I built a towfish for using with a Lowrance HDS10 sidescan.
Drawing and picture attached.
To be used with 60ft (appr. 20m) of cable for shallow use (20-30ft ( appr. 7-10m)) in freshwater lakes at low towing speeds.  We are a sheriff dept. dive team and no experience yet with our own sidescan, so this will be a first towfish for testing.  Main use will be looking for vehicles and victims.
Plan to pull the fish from a short boom off the front of the boat (20ft, 150hp outboard), use a separate battery and coil the cable in a figure 8.
Please add any suggestions/advice/additional information that would help.
The towfish is 2" PVC tubing, 6lbs (2.7kg) nose weight, 40"(102cm) long.  Towing point and transducer mounting slide fore/aft for balancing.  Current balance point is about 1/3 from nose. Total cost less than $50.
Lakes are frozen now, we probably can't test until April.

Dan, Cool! You might add more weigh to the nose 5 to 10 kg. What are you using as a com cable? Never try ed tow off the bow?

Nice fish, seen one somewhere?

Good luck and good hunting.


Hi Danl

 Grattulation, a successful Towfish. :)
 Do you use the StructureScan transducher?
 Are eagerly awaiting the first test results.



I've done a good bit of towfishing in the 20 to 30 foot range (saltwater) using a short tether. I can occasionally get away with towing from the bow, but bow movement in anything other than flat calm conditions resulted in the towfish "porpoising". My current towfish all have the transducers mounted towards the front. I plan on trying a rear mounted transducer this spring to see how much difference it can make. A longer tether with a shallow running towfish could help stabilize the towfish, but you'll probably need to tow from the stern to keep the cable free of the prop. A heavily weighted towfish can be deployed about a third of the way down the hull (and still run ahead of the prop) if it has a low enough drag profile.

* Please tell us about your cable and connections.
* Do you know if the Lowrance Sonar Log Viewer (or any third party software) can replay the Structure Scan recordings?
* Does Lowrance have an emulator for the HDS 10 (Gen2?) / LSS-1 unit?

(Edit: morning => afternoon grammar)

I really don't know anything yet about the sidescan equipment.  I just built the towfish.  On Saturday, I meet the guy who knows the electronics, cable info, etc.  I will try to get answers to yor questions.
Bow towing does seem a problem for shallow running and a shallow running angle on the cable potentially hitting the prop.  So off the stern it is....
Location of the transducer to me seems best centered right below the tow point, the center of any pitch or yaw rotation. See the diagram (two transducers in different locations shown).....any change in pitch changes the position of the  transducer more as it is farther away from the cable attachment.
So change in depth from porpoising can't be corrected for, but change in pitch or yaw from porpoising might be minimized by centering the transducer under the tow point.  Just assumptions...is that how it might work???


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