Several questions, hope Y'all can help.

[John Fennessy]

I'm working on an undergraduate thesis and am doing some bottom mapping on lake conroe here in texas. I'm going to take a stab at build a fishfinder SSS. I have 4 puck units (200KHZ) and was going to use a Lowrance mach1 paper chart recorder. The water in various areas i'm working in is very shallow 5' to 50'. The bottom still has large amounts of vegetation (there are still entire stands of trees) so a towed unit would have a great chance of getting fouled. I was thinking about making a bracket to mount on the bow and running the unit about 5' down in a fixed position? Does anybody see a problem with this? Would I have to angle the entire unit with the pucks oriented in a downward angle? Any help I could get would be GREATLY appreciated. The computer techs at the university are going to wire it up for me and they asked for any advice I could get. Rene, Great work on the testing you did, the physics dept was impressed when I showed it to them.

Thank you in advance for your help.
John Fennessy

[Jim Kennard]

Re: Several questions, hope Y'all can help.

John,

I would not recommend building the fishfinder transducer for use in an area that has large amounts of vegetation. Weeds will prevent the sonar to penetrate them and block the signal returns. Going over the top of the weeds will create a dark area without any definition, as the weeds also scatter the signal returns. These fishfinder type sonar arrays do not work very well and at best will only provide a very poor image of a shipwreck or bottom feature, and only if it is laying on a silt bottom and out in the open. I have never heard of anyone on this forum claiming that they found a undiscovered shipwreck with one of these fishfinder sonar arrays. The very few images presented here were from shipwrecks where the location was previously known.

You can easily test the above by using the existing sonar transducer mounted a few feet below the water and pointed out to one side. Mounting the single transducer tilted down 20 degrees, should be fine for this test. Typically the width of the sonar beam is very wide in the vertical plane (40 to 60 degrees at the -3db point) and narrow in the horizontal plane(1 to 2 degrees). Hope this helps. Regards, Jim



www.shipwreckworld.com

[G. Burton]

Re: Several questions, hope Y'all can help.




Hi,
Here is an image taken with a recording fishfinder, 100 ft range, with a sidescan transducer that I designed, hull mounted and only a few inches under the surface. The water was about 20 feet deep and CALM. As you can see it can be done.
Please note that this 'ducer has over 100 elements in the array. Do not expect the same results with 4 puck style elements.
Regards
G. Burton