Thread: sonar question

Here's a short video showing how 2d sonar works....(the video references Humminbird...but your Garmin 2d works the same)..

One important item the video does not explain....

*The unit xducer is "pinging" (sending) the acoustic sound pulse thru the water at several times per second....
*The processed reflection data from each single "ping" is displayed along the right vertical edge of the 2d screen (about 1 pixel wide)....
*Then the next ping's processed data is also stacked on right vertical edge of the 2d screen pushing the previous displayed ping data to the left....
*This "stacking" of each ping's data at the right of the screen and pushing the previous ping's data to the left .....creates the "scrolling" effect seen on the 2d display...

So, in effect...only the very right-most vertical edge of the 2d screen is actually what is directly under the xducer....everthing else displayed to the left on the 2d screen is "history" and what the xducer has already passed over....



Rickie

Another thing to consider when using 2d sonar, is that the ping is sent out in a cone shape ... so anything coming into the cone, regardless of from which direction, it's going to appear on the screen as though it came into the cone's front edge of your direction of travel. That would even be true if a fish swam through the cone from right to left, and you were traveling forward. The pings are also not "really" telling you how deep something is, if it's suspended in the water column. It's only telling you how far away from the transducer it is. And it could be anywhere within the confines of the cone ... so, no, you really can't be certain whether something is to the right or left or center of the cone. The unit will read all pings as if they were front & center of your direction of travel.

If your transducer is putting out a 20deg cone angle ... the "circle" of the bottom of the cone is approximately 1/3 as wide (in feet) as the depth of water you're in. So if you're in 20ft of water, the widest (bottom) part of the cone is about 7ft wide. But you also have to take into account that 10 feet down, the cone is only about 3ft wide.
If it happens to have a 60deg cone angle ... then your depth & the bottom circle of the cone would be about the same. (ie - 20ft of water & a 20ft wide circle)

I think that's how it works, anyway. So if any of you depthfinder gurus see a flaw in my description ... then by all means, correct me.

... cp

What CP said.

Not sure what degree cone angle mine is....is there any way to tell?...so is there any way to actually zero in on something other than just finding it with your jig?...thanks for the info

Originally Posted by alack

Not sure what degree cone angle mine is....is there any way to tell?...so is there any way to actually zero in on something other than just finding it with your jig?...thanks for the info

According to this : https://buy.garmin.com/en-AU/AU/mari...rod146607.html ... your transducer is 77/200kHz (60/120deg) so you'll have a wide range sonar ping cone. That's going to make it pretty difficult to pinpoint where things are, so you probably will have to find it with your jig. And that reminds me of why I've used weedless jigs for so many decades and why I don't miss 2d sonar (I have a Elite 5 DSI ... which is down scan only).

... cp