Thread: PVC cover

Hi folks, I have a question, I have sunk several crappie cover buckets using PVC for the limbs. I choose this type of material because it wont rot out should last forever but the problem I have found is my side and down scans will not pick up pvc stake beds. Anyone else found this out? I read somewhere this problem is normal when using the pvc for cover it doesnt show up on sonar?
Any thoughts?
Thanks Steve

Sonar detects differences in density of structure vs the surrounding water ...

PVC (when filled with or surrounded by water) has a very similar density as the water itself ...

Some sand the PVC to accelerate algae growth on the PVC ...

Some trap air in the PVC to create the different density factor ...

Others use PVC exactly for the reason you stated = it's harder for others to find ...

Rickie

Thanks Rickie, good explenation. I think I`ll add some wood or trap air in them to help me re-locate. You did say traping air may just be the answer?
See I gps them but where I put them at times there is current and somethimes, I think it could move or knock them over so finding them again would be very benifical to me.
Thanks Again,
Steve

Originally Posted by steve telinda

I think I`ll add some wood or trap air in them to help me re-locate. You did say traping air may just be the answer?

Air has a different density than water ... which is why the fish's air bladder is believed to be the contributing factor of fish showing on Sonar ...

Rickie

Originally Posted by rnvinc

Air has a different density than water ... which is why the fish's air bladder is believed to be the contributing factor of fish showing on Sonar ...

Rickie

Rickie ... I've always heard that as well, BUT ... then how does one explain this DI screenshot :



seeing as how it shows "fish" outlines and not simply air bladder density differences ??

Could it be the different megahertz frequencies between 2d & DI/SI ??

And as a side note : if you cap the PVC pipes to trap air (or even add wood) ... wouldn't you also have to use more weight to hold them down, to compensate for the buoyancy of the air/wood ??

Originally Posted by CrappiePappy

Rickie ... I've always heard that as well, BUT ... then how does one explain this DI screenshot :



seeing as how it shows "fish" outlines and not simply air bladder density differences ??

Air isn't the only density difference factor that Sonar detects ...

There are other substances besides air that also have a different density than water (fish flesh, scales, structure, bottom composition, etc) ...

Air would be in the "less dense" category vs water ...
Flesh, scales, structure, etc would be in the "more dense" category vs water ...

Either side of the "vs water" density would be different than the water density itself ...

Rickie

Originally Posted by rnvinc

Air isn't the only density difference factor that Sonar detects ...

There are other substances besides air that also have a different density than water (fish flesh, scales, structure, bottom composition, etc) ...

Air would be in the "less dense" category vs water ...
Flesh, scales, structure, etc would be in the "more dense" category vs water ...

Either side of the "vs water" density would be different than the water density itself ...

Rickie

OK, I got all that !! So, if a 2d sonar beam was restricted to a narrow fan shape by blocking the front & rear of the cone ... would/could it produce a similar image as the DI ?? It wouldn't, would it ?? But, is it the shape of the crystal or the frequency being transmitted that determines the image ?? Or am I comparing apples to oranges, here ??

Originally Posted by CrappiePappy

OK, I got all that !! So, if a 2d sonar beam was restricted to a narrow fan shape by blocking the front & rear of the cone ... would/could it produce a similar image as the DI ?? It wouldn't, would it ?? But, is it the shape of the crystal or the frequency being transmitted that determines the image ?? Or am I comparing apples to oranges, here ??

The shape of the piezo only affects the beam shape ... round piezoes create cones / bar piezoes create slices and fan beam shapes ... (size affects beam
Angle) ...

If we were to connect a bar shape piezo to the 2d wire channel = we would have a fan (or slice) shape 2d Sonar beam ...

Fish echoes from this scenario would be painted in the 2d image as a colored dot (depending on 2d palette choice) ... just like a DI fan beam paints a white dot ...

A "dot fish echo" vs an "arch fish echo" we know is simply created by target time in the Sonar beam ... a fan beam doesn't allow the target to be pinged as many times ... and the few times that target is pinged in the fan (or slice) beam, the target is basically the same distance from the xducer (or negligible difference anyway) ...

Now to expand this scenario some ...

If we increase the frequency of this scenario's 2d fan beam (to 455kHz or 800kHz) ... we may even see some these 2d fish echo dots that look like fish ... but colored (depending on 2d palette choice) ...

Basically ... imaging is imaging because of higher frequency and fewer pings on the target ...(and processing the returns into several shades [by strength of return] of the same imaging palette color choice) ...

Rickie

PVC at the base of a drop.

Rickie, the picture you sent reggarding the structure being pvc, is that one with air traped inside like you suggested?
If s0, I could seal both ends and hopefully have the same readings once sunk?
Thanks again