Topic: Minimum tow fish depth

[sonar2000]

Is there a minimum depth for tow fish operation.
Is there a depth which tow fish is not as viable as the regular SI? 
When should we consider tow fish for a display? 

Chuck

[Rickard]

Chuck,

Clever question that's hard to answer. There seeems to be a tradeoff between proximity to target and cable length. A long cable means close to target but weak signal. Short cable, like with a hull mounted transducer, means far from target but strong signal. I found when using my 50 m towfish cable I must stay closer than 10 m from the seafloor to get acceptable coverage. When targets are deeper than about 10 m a towfish seems to afford significantly sharper images. At 30 m the targets must be substantial to be seen from the surface. So my rule-of-thumb has become: shallower than 10 m - no need for a towfish, deeper than 10 m - use the towfish (if I search for smaller targets). In wavy conditions a towfish always helps regardless of depth, but then the cable doesn't need to be 50 m!

The images show the same wreck as it looks when using the towfish and when scanned with a hull mounted transducer the same day.

Towfish



Hull mounted transducer

[sonar2000]

Thanks, Rickard.  And answers that I can understand.  The picture help a lot also. Most of our waters will be under the 10 meters of depth and the targets will be small. Very seldom do we get deeper than 10 meters and then it is usually for larger objects.
If we do get deep water then we go to a true side scan system. 
Just wanting to make sure we were not missing something. 

Thanks again for the good explanation.   

Chuck