Other Interest > DIY - Side Scan Sonar and towfish

Towfish setup - for reducing wave motion

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Boue:
Hello,

Firstly, wow, what an amazing forum, so much knowledge.

I am a proud new owner of a HB Helix 9 with Mega SI+ transom mounted ducer, which I intend on using for seabed habitat mapping in seawater approx 10m to 50m deep.

I am at a fairly exposed coastal location, so the sea is rarely as calm as I would like it, which means the number of days where the sea is flat enough to capture really good SI data are limited.

I am therefore thinking that a towfish would help removing the roll and pitch of the boat (21ft motor cruiser with outboard).

Does anyone have any recommendations for a setup to simply remove the motion of the boat. I don't need to get the ducer much deeper, just remove the wave action. I also have a down rigger on the boat.

I am considering lowering the down rigger just enough to clear the outboard, then streaming a towfish 5m or 10m behind it?
Would such a setup achieve my objective of steadying the ducer from the motion of the boat?

All and any comments or advice greatly appreciated.

Thank you
Tim

Rüdiger:
Welcome to the forum Tim :)

You're right, a towfish is the best solution to minimize boat and water movement. Here in this forum you will find many examples of construction. I also only use three standard extension cables for towing, but with an additional line for strain relief.
Have fun building it yourself and let us be a part of it.

mvh
Rüdiger

abraquelebout:
hi
Rüdiger is on the right.
I use towfish in salt water for various deep (3 to 60m),, but 10 m câble seem's short.
Think there's few meters on board to connect the unit (4 or 5m) and if there's more waves the movements of the ship give a wrong traction to towfish (some bad movements).
My first short towcâble is 30 m and the second for 60 m deept is100m, with the 30 m i get a good result with a  bad weather (1m short waves and 15 to 20 knots wind) at 7 to 10 meter depht . ..the towcâble is all over  board at this moment.

Boue:
Hello both,

Thank you very much for your advice.
Rüdiger - do you use a downrigger with your towfish?

Thank you

Rüdiger:
Hi Tim

I don't use a downrigger, as an alternative to the usual rocket shape for a towfish, here's a good idea:
http://www.treasurenet.com/forums/shipwrecks/579733-towfish-vs-downrigger.html

mvh
Rüdiger

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