By Jeff Boyer – Sonar GPS Workshops LLC
T
his issue, let’s tackle another common
question Capt. Jack and i often get at our
seminars. “How do i know where the
fish on my screen are in relation to my boat?” it’s a great question. i remember when Carl
lowrance introduced the “little green box”, he called
it a Fish lo-K-tor. He intended it to help us locate
fish. Unfortunately, plenty of sonar users still today
remain in doubt about the actual location of those
fish that show up on their screen. let’s be sure you
are no longer in that category.
When determining fish location, one of the first questions should be, “Is the fish in the cone angle, or not?”
Note the several fish marks in the below screenshot. (screenshot 16.) Some are in the cone angle, some are not. if you are unsure who’s in or out, remember, the echoes returning to your transducer always appear first on the right side of your display. They then travel across the screen right to left. (Just think of your boat position as being in the top right corner of your display, just above the 15.1 upper limit reading.) So any object appearing on the right edge of the display is in the cone angle. as long as it returns an echo, it continually updates its marking on the right side of the display. (That’s why the bottom contour marks
continually across the entire display, because it is continually returning echoes to the transducer.) The same principle applies to fish echoes. as long as a fish is in the cone angle, he returns an updating echo displayed on the right side of the screen. But as soon as the fish leaves the cone angle, he no longer returns an echo, and his “fish mark” stops updating on the display. it simply travels across the screen, eventually disappearing on the left.
Now look at the next screenshot. (screenshot 16a.) You’ll notice some of the fish marks now circled in either red or green. Note all the fish marks circled in green are still updating when i stopped the chart display. Those fish are still in the cone angle. The fish marks circled in red (as well as other uncircled fish marks on the screen) are all out of the cone angle. i like to say they are “history”, because they currently are not at our present location.
let’s first deal with the green circled fish in the cone angle. WHere are they in the cone angle? true, one is about 20’ deep, one is 24’, and the other just below 30’. But does that mean they are directly below the boat? Not necessarily. it means they are directly in the cone angle. So it’s critical to know the coverage area of our cone angle.
Find the cone angle pattern of the traditional 200KHz sonar transducer in the photo. (Cone angle diagram next page.) (odds are, unless you requested
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