Quote Originally Posted by BobB View Post
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
And on a 60deg cone angle of a wide angle 2d ... those fish at the outer edge of the cone would be shown as being at the correct depth ??? I don't think so. ALL images in sonar are painted as how far from the transducer they are ... not how deep they really are.

I already use the right triangle calculation to figure how deep my jigs are running, by how much length of line I have out, as long as the angle of the line is approx. 45deg. I already know to multiply the length of line by 0.6 to determine the depth of the jig.

But, in regards to Kosmo's screen image ... I see what you're saying --- that the fish below the thermocline (in the screen image) may not "actually" be that deep, but in fact just "that far away" from the transducer. Point taken.

It would not, however, be enough for me to go back to 2d or even go to a unit that has 2d included with DI. I'm perfectly satisfied with the picture quality images that my DI unit provides, as opposed to the narrow cone angle and finger painting images that my previous 2d 20deg cone angle units used to provide.

... cp