Get Serious About DepthfindersGet Serious About Depthfinders An in-depth article explaining how depth finders work, and how to use them to catch more bass.
By David Wharton
Advances in bass fishing the past few years has been nothing short of astounding. The boats are bigger and faster, rods are more sensitive and lighter, troll motors have as much thrust as small outboards, and lures are more lifelike and effective than ever.
The same is true with sonar. The days of a flasher with light bulbs that go out, a motor that vibrates the entire boat, and makes that nerve rattling noise are gone. It's simply amazing. The advances in liquid crystal technology have given us flashers with no bulbs to go out, and no moving parts to make any noise whatsoever. These units are easy to read, very dependable, and are rather inexpensive. Liquid crystal technology has also given rise to a state-of-the-art, high-resolution fish finder called the LPG or liquid Paper Graph. This technology has allowed Zercom to duplicate the performance of the popular, but obsolete, paper chart recorders. The dual beam sonar configuration provides not only excellent bottom detail, but also records fish targets as true fish arches, as did its predecessor, the paper graph.
Understanding how sonar works will be of help. Electrical impulses from the unit are sent to the transducer where they are converted into sound waves. These sound waves are sent into the water in a controlled beam from the transducer. Objects within this beam reflect the sonar back to the transducer. The transducer accurately measures the distance to these objects based on the time it takes for the sonar to return. Each object (bottom, fish or structure) reflects the sonar uniquely, providing information about its makeup. This information is then converted back into electrical impulses by the transducer and sent to the unit for display on the screen. The information is the same whether it is displayed on a flasher screen or LPG screen. The difference is how it is displayed and interpreted by the user. The information is displayed instantly on a flasher screen, whereas the same information takes longer, but has much more detail on the LPG screen. A well-equipped boat will have both a flasher and LPG, because of the differences in the display speed.
Flasher-type fish finders are better in certain fishing situations. Because they display information instantly, flashers are better for use while running the boat at higher speeds. This is especially true if you are unfamiliar with the lake. You would be aware much quicker of dangerously shallow water. Flasher-type fish finders are also better while fishing certain types of cover, such as hydrilla or other very dense bottom cover.
Underwater vegetation can confuse some depth finders because the sonar waves are diffused, absorbed, or reflected erratically. It is very important for the fish finder to read through the hydrilla to the bottom so you will have a true depth. Some liquid crystal recorders will read only the top of the hydrilla, and not give an accurate bottom depth. Bass in the hydrilla often relate to the bottom changes, so it is very important that you are aware of these changes. A flasher-type fish finder will allow you to see these changes and keep the boat in the proper position.
If the top of the hydrilla is seven feet deep in 10 or even 17 feet of water, which is common during summer and fall, then it is very important for your fish finder to be able to read through the top of the hydrilla to the true bottom. There is a big difference between 10 feet and 17 feet, because quite often the bigger bass will be relating to the bottom in the deeper hydrilla. Flasher-type fish finders are usually better if you are fishing in real shallow water during spring or fall. These type fish finders will often read in a foot of water, whereas a liquid crystal recorder is at its best in a little deeper water.
Now is probably a good time to talk about the cone angle. As stated before, the transducer sends down sonar waves. These waves are cone shaped, narrow at the transducer and wider as it gets deeper. As a rule of thumb, the bottom coverage is about one-third the depth. In other words, if you are sitting in 20 feet of water the fish finder will cover a six-foot circle of the bottom under the boat. As you get deeper this circle will get larger, and as you move shallower the circle will be smaller.
Understanding this concept is critical in getting the most from your fish finder. The shallower you get, the less likely you are to see a fish displayed on the screen, simply because of the restricted coverage. As you idle through a shallow area chances are you will spook a bass before it is displayed on the screen. It is extremely important, while in shallow water, to note bottom changes, cover, or structure that is likely to be holding bass. Chances are you will not see a bass on the screen in shallow water, but that does not mean they are not there. You have to fish the likely areas and assume that the bass are present.
A fish arch forms as the fish moves through the sonar beam. Due to the transducer beam angle the distance to the fish decreases as it moves into the beam, and increases as it moves out. When the chart window graphs this distance change, an arch appears. Boat speed and movement of the fish greatly affect the shape of the arch. When moving slowly, a fish creates an elongated arch. When moving fast the arch appears shorter. A partial arch forms when the fish does not move through the entire cone. The longer a fish stays in the cone, the larger they will appear. A big bass may appear smaller if it is only on the edge of the cone. Also, a smaller bass may appear larger if it is stays in the cone longer. In other words, the size of the arch does not necessarily correlate to the size of the fish.
On the flasher screen fish appear as "blips." The darker the "blip," the longer the fish stayed in the cone. A lighter "blip" indicates a bass on the edge on the cone. It is important to remember that the sonar cannot distinguish between a fish and some other object suspended in the water. Regardless of the object the sonar detects, each will be drawn as an arch or "blip."
Knowing the characteristics of bass and the type of water they prefer is very critical in the use of a graph. Every thing you see is not a bass. The sonar cannot distinguish between a gar, a carp, catfish, or a plastic jug for that matter. If a fish appears close to the bottom on the edge of a drop-off or creek channel, or close to cover, it probably is a bass. If the fish are away from cover, suspended over deeper water, or generally in areas that are not bass habitat, then they probably are not bass, but some other kind of fish. Even if they are bass, the chances of catching them are not good. You would be better off going to a more likely area, where the bass are in a position to be caught. Bass that are close to bottom, or cover, are fish that can be caught.
Installation of the transducer is the most important aspect of getting a good read out on the screen whether it is a flasher or graph. The sonar cannot read through air. The best and most expensive unit will be rendered useless if the transducer is not installed properly. Most bass boats now come as a package deal pre rigged with fish finders. Most of the time the transducers are mounted inside in a designated area close to the transom. If you are not getting the read out you expect chances are there is air under the transducer or an air bubble in the gelcoat of the boat. For the absolute best read out the transducer should be mounted on the outside of the boat. Usually with this type of installation, you will lose some of the high-speed operation, but for idling around over likely areas, this will give the best picture. A good combination is to have a flasher with an inside transducer for high-speed operation, and then an outside mounted transducer for the graph for slower speeds and a more precise picture. The front fish finder should have the transducer on the troll motor. This will give you a picture of the bottom closer to where you are fishing in the front of the boat.
Interference from the troll motor or another fish finder can cause a distorted picture and make you miss some important information. Troll motor interference can be eliminated by properly grounding the troll motor. Zercom has eliminated interference from other fish finders by using different frequencies for the front fish finder and the back fish finder. These can be run at the same time without interference because of the different frequencies.
We have talked about the advantages of the flasher and the advantages of a graph. What would you think if you could get them both in one unit? Wouldn't this make navigating a lake or looking for fish much easier. The Zercom LPG 2000 can do exactly that. This unit has what they call a Real Time Sonar (RTS) window on the right of the screen and to the left of the RTS window is a chart window. The Real Time Sonar (RTS) window shows instantaneous sonar return from the bottom, structure and fish that are within the transducer beam. The RTS window updates the new sonar information much more quickly than the chart window - up to 30 times per second in shallow water. The RTS window responds to quickly changing depths similar to a flasher. Interpreting the RTS information requires some skill. However, comparing the RTS presentation with the information on the chart window makes it easy to understand. The chart window creates a historical log of sonar returns from the RTS window. As the boat moves, variations in the depth and sonar return change and are charted to form an image of the bottom contour. The most recent sonar returns are charted on the right side of the window and as new information is received, the older information is moved across the display. You can watch the RTS window for instant information and the chart window for detail of the same information. That's the best of both worlds. The LPG 2000 will give the user the best information available. You have to use this information to your advantage to find fish quicker and easier. In most instances it is better to look for cover, bottom changes, or other likely areas that bass will be holding on, than it is to see fish on the screen. To see fish on the screen everything has to be just right. And, really, in the real world how often is everything just right?
Occasionally you will see fish and be able to catch them, and most often this will be in water that is more than 15 feet deep. Most bass fishermen will fish in water less than 15 feet most of the time, or will be vertically jigging in hydrilla where it is much more important to see the bottom than it is to look for fish in vegetation. You can become cross-eyed, nearly blind, and - trust me - your eyes will be watering, before you can find a "blip" that looks like a fish if you are sitting in 15 feet of hydrilla.
Take the time to learn the areas you are fishing. Get a good map that shows the creek channels. Creek channels are the key to finding bass in most reservoirs. Once you have a map, and have studied it, use the depth finder to locate these channels.
You will need marker buoys to mark the bends, high spots, and brush. Idle with your boat in a zigzag manner so as to cross the channel back and forth. When you see a likely area throw the marker, and continue until you have the area mapped out.
You can use the same method to follow underwater points out into the lake. As you zigzag across a point mark the likely areas with buoys so you have a good understanding of the bottom contours. This is the way you learn a lake. It takes time, a lot of patience, and a good fish finder. Use a triangle method to line up on the areas once you have found them. Line up a tree close to the shore with a tree further away to get an exact line on the spot. Do this even if you use a GPS. GPS units will get you close, but lining up trees or other objects will get you exactly on the spot. It doesn't hurt to mark these in a book for future reference. Do not rely on your memory for these exact lineups.
The Zercom LPG 2000 is a serious advancement in fish finding technology. Combine this technology with some good common fish sense and you are well on your way to finding more bass. A lot of people can catch bass if they find them, but there are not nearly as many people that can find them!
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