I've been using digital depth finders since 1989 and flashers since before I care to mention.
When I first started using depth finders, I just turned the unit on and used it in automatic mode.
That's fine for seeing the depth of the water but even a cheap depth finder can give you more information .
The key is learning to adjust the sensitivity in manual mode and how to interpret what is displayed on the screen.
A basic knowledge of how a depth finder works will help you to interpret the images display on the screen.
All depth finders use sonar.
Basically, your depth finder uses a transducer to send out and receive sound waves.
The sound waves travel out in the shape of a cone with the top or point originating at the transducer.
These sound wave bounce off of the bottom as well as fish and structure and are reflected back to the transducer.
The transducer then converts the reflected signal in to electrical impulses and the head unit processes and displays the results.
Since the depth is determined by using time and speed of the return echo/sound wave.
This is a very basic explanation but it should help you to understand how more than just the depth of the water can be determined with a depth finder.
It's obvious that when a fish passes through the inside of the cone of sound waves, it will produce an echo.
So will underwater objects such as trees, stumps, and etc.
Even when the depth finder is in auto mode, it will display most of these things.
However, by going to manual mode, you can see more! For instance, if there is a thermocline, you can adjust the depth finder to show it.
This is useful because some fish like to suspend at the thermocline.
I almost forgot to mention, if your unit displays fish symbols, TURN THEM OFF!!! You will see a better representation of what's really under you if you don't use fish symbols.
I have noticed that a really big fish symbol may in actuality be 2 fish close together.
You can also tell if you have a hard bottom or soft bottom.
A hard bottom will show up as a thick line on the bottom.
This is because a hard bottom gives a good return signal.
A soft bottom absorbs more of the sound and gives a fainter echo.
Hence, a soft bottom will show up as a thin line on the bottom.
Another thing to remember is that since the transducer sends out sound waves in a cone shape, some things on the display are not necessarily under the boat.
For example, you may be in 30 feet of water and at the bottom your cone diameter may be 30 feet.
This means that a fish 6 inches off of the bottom anywhere in the 30 foot diameter will show up on the screen.
On the other hand, a fish that is 5 feet under the boat but 20 feet away will be outside of the cone and will not be displayed on the screen.
This should help to understand how a depth finder works and get you started in becoming an expert at adjusting and reading your depth finder.
I'll go over how I set my depth finders up and more depth finder information in the next article.
Remember, the only way to really learn how to get the most out of your depth finder is to get out and play with it.