Lowrance dead zone

[Ron T.]

Any Ideas on how to clear up the clutter that seems to occure on the bottom that obsruucts the view of the true bottom. Seems to only occure on a hard or steep bottom. This is the HDS 10. I have the bottom line setting on , drop a drop shot streight down and the bait will dissapear long before accually hitting the bottom. Frustrating not being able to see what might be swimming on the bottom 3 to 5 feet. Didnt have this issue with the old lcx110 or the trusty x17.

[WackySenko]

When drop-shotting do you have the system set for the 83kHz? I learned that you can see your drop-shot much better that way. I hope that helps.

[Ron T.]

Not a problem seeing the bait untill it hits the cluttrer filled last 3 to 5 feet.

[GregD]

I was wondering this too. I see the same thing on my HDS5. I was hoping someone who really understood how these units work would jump in but in the absence of that so far, here's what I'm thinking is happening...

Your transducer is emitting and receiving the sonar signals over a cone angle that means it's covering a circular patch of the bottom of the lake at any given instant in time. The size of that patch is dependant on the depth of the lake bottom. Could be 2' in diameter if you are in shallow water, or it could be 10' if you are in deeper water. But if the bottom of the lake is sloping at a steep angle, the circular patch is actually oval and part of it is hitting the bottom in shallower/deeper water than other parts. So the graph is processing depth data returns at different levels and has to display those different depth levels in the form of the "noise/clutter" you are seeing. What appears to be the bottom on the screen is actually the deepest returns in the cone angle "contact patch" and the "noise" is returns within the cone angle that are at a lesser depth. The top of the "noise" is the returns coming from the shallowest returns.

If that is true, I have no idea how you would set the unit up to still be able to see your lure in that zone. It may not be possible as it would be a very small signal in the midst of much stronger returns from the lake floor.

[Delaney]

GregD, you put this in a very understandable way, which is another reason that I wish flashers were still available. LCD images disappear in that zone. When I go over a place where I know there is a vertical under water bluff, all I get is a sloping picture that is an average of the two depths, and you don't see what's between the two different depths. Back in the flasher days, going over an underwater vertical bluff you would get two separate readings that would show fish on the bluff between the two readings.

[Ron T.]

Greg, thats the same thing I was thinking and you explained it well. Only thing is I dont remember getting this on my other graphs. With my x17 I was able to find fish on steep rock and points and catch them . With the HDS10 its a completely differant animal on the points and rock. Hard to have confidence in going virt when I cant make out whats there or not. Thinking about reinstalling the x17 ??????? Anybody have any other suggestions ?

[GregD]

Maybe this should/could be moved to the Lowrance Product Forum and Ken Sauret could weigh in?

[ash]

Maybe this should/could be moved to the Lowrance Product Forum and Ken Sauret could weigh in?

We dont do shadow topics typically, but I think this is worthwhile for anyone with an HDS unit to learn the response from Lowrance, I moved the topic to the Lowrance forum (thanks GregD) and left a copy on the main board.

Good luck in your quest, PS my ole boat has both a flasher and a 17x

[WackySenko]

The diameter of the cone at the bottom is: depth divided by 5 and multiplied by 2.
Example: 15' depth divided by 5 is 3 then multiply that my 2 which equals 6' a cone with a bottom of 6'.

[GregD]

The diameter of the cone at the bottom is: depth divided by 5 and multiplied by 2.
Example: 15' depth divided by 5 is 3 then multiply that my 2 which equals 6' a cone with a bottom of 6'.

Isn't there a different cone angle depending on the frequency of operation?

[Bayou Boy]

Yes, cone angles do very. Example: The rule of thumb for a 22 degree cone angle is 1/3 of depth is diameter of bottom area covered.

Learn to go to manual settings. You have no control over the power output of the signal you can only control the gain or ability to receive. Equate your sonar gain to your truck radio volume. You have no control over the power of the radio station's signal or the strength of the signal you receive; all you have control over is the volume.

As you drive further away from the station the weaker the signal becomes e.g. the deeper the water the weaker the return signal. As you turn up the volume on your radio to hear your favorite song you start hearing "Static" or interference too... Same with your sonar; the higher the gain setting the more you are amplifying the un-wanted info too.... Hence the more difficult it is to get a good clean read on a steep slope or drop off....

[Delaney]

Wonder why no comments from Lowrance at all on this subject? Seems strange!

[timegg]

I thought I would bring this up again to see if anyone has a fix for this problem. My HD5 does this all the time, the steeper the bank the worse the dead zone. Maybe Ken could help with this or anyone else. thanks tim.

[mark poulson]

Greg D nailed it.
I fish sometimes with a guy who actually did a video on sonar, and he said what I was seeing was the steep adjacent structure.
After he 'splaned it to me, Lucy, it made perfect sense.
If you run down imaging at the same time, you can actually see the rising structure that corresponds with the "dead zone" on the 2d sonar.
That's the only "fix" I've found. Maybe it's possible to put a "cone of silence" around the transducer, to focus the beam and restrict the returning signals, but I bet that would probably come with it's own set of problems.

[Marc]

Guys, what you are seeing is a limitation of sonar that you do little to overcome, regardless of brand or model. Even modern flashers have the same limitation, because the cone angle of the transducer sends the signals out in a wide path that doesn't play well on steep drops or any rapid depth change.

The only way to improve the situation is to use a narrow cone transducer. The flashers of years past had a very narrow cone angle (most were less than 10 degrees, compared to modern cone angles of more than 20 degrees).

In the old days the units didn't have enough power to handle wide areas that modern units are capable of, nor did they have adequate software to process the signals. The flashers were also intended to primarily show the bottom directly under the transducer, and any object in between the bottom in a direct line below the transducer. So they are great for showing the true bottom depth, but lousy for showing the degree of slope, or for showing fish or objects off to the side of the boat.

I haven't shopped lately, but you used to be able to buy smaller cone angle transducers from aftermarket companies like AirMar. Might want to check this out. The universal sonar transducers in trolling motors are generally a few degrees smaller cone angle as well, and is why I used to use a US2 on my Maxxum. I don't any longer.

Now I prefer to see the "dead zone" so that I can judge the dropoff and easily find it as well. I don't worry so much about seeing bass on these spots, as even with a tight or narrow cone angle I learned you only see a fraction of the bass that are actually there anyway; so now I just fish them and let the fish tell me if they are there.

Hope this helps clear up the dead zone.

ciao,
Marc Marcantonio

[Ron T.]

Would be cool if Lowrance could sell a narrow cone angle transducer for the guys fishing steep lakes . Even better if we could adjust the cone angle to suit current conditions. Just a thought.

[Marc]

Ron, check with Airmar (Google them) to see if they still sell a narrow cone angle transducer. As long as it is 200 kHz you will be able to use it.

ciao,
Marc