Direction of travel

[broke]

Might be a dumb question, but does the shape of a fish on my lowrance have anything to do with direction of travel. I often see very elongated fish on the screen. Maybe he is going the same direction as the boat? or is it the Locke Ness Monster . Another question is, where is an object when it first scrolls onto the screen in relation to the transducer? . We are coming right along with fish catching. Caught about a dozen on Saturday in Beaverdam and a few upstream from the mouth on boards and downlines. All were in the slot but one and we had him for supper Saturday night. What we know about fishing for Stripers we learned from the fellows here on this forum. Thanks to yu'all. More than a few of you could make a decent living taking folks out for $$$$$$ but I know that would interfere with the fun.

[mwardncsu]

One thing to keep in mind is that your sonar is essentially like a flashlight facing down into the water, and then displaying anything that "breaks the beam" as the sonar "beam" penetrates deeper into the water, the beam gets wider - shaped generally like a cone. So, you can't specifically tell if return is in front, behind, to one side or the other of the cone by just from the return. If you get a faint return that gets stronger then it is the object entering the sonar cone - this could be a stationary object that you are moving over top of as your boat moves, or it could be the object moving into the cone of its own power. If you are marking a strong return and it stays there on the screen, then it is likely a fish moving with you - or as you say - the Loc Ness....



;D

The other thing to remember when viewing the "depth" of the return - is that this is not necessarily the "depth", but rather than distance of the object to your transducer - a mark at 20' could be 20' below you, but could also be 20' to the side, 20' somewhere along that arc.

Dual-frequency sonar setups can help you nail it down some - for example, the Lowrance HDS 83/200 transducer has a wider cone on the 83 side than the 200 side (for this discussion I'm setting aside the fact that the 83/200 is actually a single frequency transducer, to which the HDS does some signal processing to extract the "83" out of the weaker side-lobe returns.... ) In this scenario, if you see a mark on the 83, but not on the 200, then you can likely be assured that the fish is not underneath you, but off to one side (or forward/aft). Therefore, understanding the cone angles of your specific transducer/frequency is important so that you know what amount of area you are covering at a given depth.


Here is some info from a Lowrance sonar tutorial that is helpful.....

Why fish arch....

The reason fish show as an arch is because of the relationship between the fish and the cone angle of the transducer as the boat passes over the fish. As the leading edge of the cone strikes the fish, a display pixel is turned on. As the boat passes over the fish, the distance to the fish decreases. This turns each pixel on at a shallower depth on the display. When the center of the cone is directly over the fish, the first half of the arch is formed. This is also the shortest distance to the fish. Since the fish is closer to the boat, the signal is stronger and the arch is thicker. As the boat moves away from the fish, the distance increases and the pixels appear at progressively deeper depths until the cone passes the fish.

If the fish doesn't pass directly through the center of the cone, the arch won't be as well defined. Since the fish isn't in the cone very long, there aren't as many echoes to display, and the ones that do show are weaker. This is one of the reasons it's difficult to show fish arches in shallow water. The cone angle is too narrow for the signal to arch.

Remember, there must be movement between the boat and the fish to develop an arch.

Here are a few other links to some good tutorials on sonar which helps to gain an understanding...
primus.lowrance.com/icr/Sonar/Chart%20Tutorial.htm

www.jamestowndistributors.com/userportal/document.do?docId=172

www.jamestowndistributors.com/userportal/document.do?docId=345