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So .... with the 200 khz 2d and the thermocline at 20'......fish on the outer edge of the beam would be 20.5' from the transducer.
With 455 khz DI fish on the outer edge of the beam would be 25.2' from the transducer .....and could show 5.2' below the thermocline.
With SI ... the fish depth could be very radically wrong in deep water.
If you extend the thermocline to 30' deep, the outer edge of the 455 khz beam would be 37.5' and the 200 khz beam would be 30.7'.
Just thought of another factor that would come into play ..... With the 2D, the top of the arch would indicate the true depth of the fish if it passes thru the beam directly under the boat ..... the shape of the arch will tell you if the fish passed directly under the boat if the transducer is properly adjusted.
With DI, you can't tell where the fish really is.
So,a fish at 20ft. deep ,at the fartherest distance on that si view would show as 77ft. deep on si/di views and not been seen at all on the 2d (which was set to 200/83khz) correct?Quote:
Originally Posted by BobB
Kosmo ..... I calculated that based on a 75 degree angle from vertical ....... which isn't correct for the DI beam since it is 75 degree total coverage....37.5 to each side. I was also assuming that was an Onix image.....It is even more complicated if that is a core unit image.
Since 455 SI is virtually 180 degree coverage each side..... anything out to the side up to 107' from the transducer would be in play.....a fish that is 20' deep, but 105' from the transducer would show 2' off the bottom in the water column.....With that water depth of 107'.
This picture is from a 998,using the 455khz with the 180° of coverage .u are correct.the di,generated from the si elliments can make fish location very hard to determine on the di.well accually, looking at the si alone.Still,fish location is hard to determine.
My head hurts trying to follow this.
What does the thermocline look like in each 2D, DI, SI?
Since the DI is calculated from the SI on the core units, the DI coverage angle is a lot more fuzzy....
It is good to be aware that if you want to know how deep the fish are holding .... The more narrow the beam, the better..... and the slant range effects associated with SI and DI can cause some things in the displayed image to be deceiving.
ON DI IF IT IS A BRUSH PILE U CAN TELL IF U WENT ON TOP OF IT OR TO ONE SIDE OF IT AND CAN DETERMINE THE HEIGHT IT IS IN WATER EVEN IF U GO TO ONE SIDE OF IT
I'm guessing that's there's all most no fish deeper than 30ft. in that picture.I'm guessing that the oxigen level is to low deeper.
You know how far the top of the pile is from the transducer .... that's not necessarily how deep it is depending on how for off to the side it is.Quote:
Originally Posted by genec