Thread: Thermocline????

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.

Originally Posted by BobB

With a 75 degree beam angle ..... Fish on the outside of the beam will be very far from the transducer and may be painted on the image as being at that depth....

In Kosmo's image .... if you assume the thermocline is at 20', the fish at the outside of the DI beam, at the level of the thermocline, could be 77' away from the transducer with the 455 75 degree beam angle .... DI may assume those fish are 77' deep.

Run some numbers thru this calculator and the results will surprise you... Right-Angled Triangle Calculator

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?

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.