Topic: 2D readings Troling motor vs Transmon

[mike fish]

Last year I had asked about why if I run my Vexilar on Trolling Motor it shows more detail then my 798 at the console using the Transom TD. Didn't really get to bottom of that last year.
This year I upgraded to 2-999's. So for giggles I mounted my 798 on a portable case and was going to give it try this winter icefishing but in the mean time decided to try it upfront on TM. Now again I'm getting better readings and more detail on 798 then at the console 999. If I had got these kind of readings in past I'm not sure I would have upgraded, well maybe I still would have, it's always fun to get new toys but you get my point.
The question is why does this happen? Is there reflection off hull or something stopping TD from recieving signal back?  I have a 16.5' tin boat. Does this happen on glass boats too? I did this about a month ago and been messing around moving TD and even borrowed a 2D TD from someone to try also on transom with the same results.
I can post some pics later tonight so you can see but maybe someone already knows the answer to this.
 Thanks Mike

[rnvinc]

There is the possibility that the hull is creating turbulence that the transom xducer is trying to transmit thru ....

Rickie

[mike fish]

Maybe. ? I've been questioning this problem since new so possible. Especially after the day at the Res. and I know there's lots of fish in there and that was verified on a another trip when we took our Vexilars with.
 
More info: Original HDSI is mounted directly to starboard transom and then I have another HDSI and 2D mounted on a separate boards and clamped to transom so I can move and adjust them. I've moved them both all over transom and still same results. Trolling motor is on bow so TD is away from the boat a bit.
I even held 2D TD off to side of boat best I could and didn't seem to get any better results but that's some what inconclusive because it was difficult to hold steady.
Do the plastic mounting boards offer anything besides adjustability and not a ton of holes in transom? I think I asked this before but don't remember. Does the SI ping while looking at 2D screen?
Just trying to put my finger on what is happening here.

[mike fish]

798, 999, 798, 999 respectively.

[mike fish]

A couple more. The GPS coordinates are with in 2-7 thousands in all these screen shots.
The 2nd pair of shots the hump on bottom is on left in 798 and center of 999. Lines look like interference but may be debris or dirty water. Water is still a little dirty yet.  thoughts?
Some of the SI shots from HDSI TD that was in center of boat gave some decent results.
After reviewing some more this morning I have a list of different things I want to try next time out.

[rnvinc]

The vertical lines in the 2d is crosstalk interference ...and this will cause some issues in performance ...

If your units are Ethernet connected you can select to use one xducer for both units to eliminate crosstalk ...

If your units are not Ethernet connected you will have shut the Sonar off of one to eliminate crosstalk ...

Please post some more examples after you find and eliminate the crosstalk ...
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The plastic mounting boards do have a slight advantage on getting effective high speed readings by placing the xducer housing behind the transom plane just enough for the water to begin its natural tendency to rise back to surface level after exiting from under the hull during travel ...



Rickie

[mike fish]

Units are not connected. It looked like interference to me too but it isn't there all the time but the last pair shows the worst images.
My hull is considered a deep "V". Where would you expect to find more turbulent water off back of transom? Near center of boat or outer edge of boat?
The plastic board makes some sense in that retrospect.
My next chance out probably won't be till next week.

[rnvinc]

Experiment with turning the sonar off and on to see if that's the interference culprit ...

Crosstalk is usually worse in deeper water because the 2d cones have spread out farther as the water gets deeper ... (Notice your deeper examples show worse vertical lines than the shallower examples) ...

Rickie

[mike fish]

Yep, I should have thought of the deeper water. I actually had switched it to 83/200 not to long before that too from 200 now that I think about it.

[mike fish]

Some Trolling motor shots with 999.
Last one is transom.