Next to the proper safety equipment, the sonar unit is the most important item on a fishing boat. With proper use and practice a good sonar unit will show bottom, baitfish, game fish, weeds, bottom composition, weed type and many other mysteries of the deep. Most boat buyers prefer to just take the sonar unit that is part of a boat package. This can be a mistake as most package sonar's are lower quality units to keep the package price down. The following tips will help you determine the quality of a sonar unit so you will get the basic features you need for maximum performance.

Vertical Pixels- The most important factor when choosing or comparing sonar, vertical pixels relates directly to lines of resolution. Pixels are simply little dots that are turned on or off to produce a display screen on all liquid crystal sonar units. The higher number of vertical pixels the better the unit will separate targets and be able to show detail. A sonar unit doesn’t become capable of showing enough detail to use in fishing until the vertical pixel count starts approaching 240.

Power- Sonar power is rated two different ways, peak-to-peak wattage and RMS wattage. The differences and methods of determining these ratings are beyond the scope of this article but be aware to compare the same rating when comparing two or more units. Sonar power determines how deep the sonar can read, how small a target can be and still register and allows the user to see their jig, thermoclines and even determine weed type! Most sonar shoppers buy too little power. If you really want to see bait fish, subtle changes in bottom composition, and fish close to the bottom, more power is necessary. As a rule the minimum power ratings are about 1500 watts peak-to-peak and about 250 watts RMS.

Transducer Cone Angle- The "eyes" of a sonar unit, the transducer is mounted on the rear of the boat or on the bow trolling motor and sends and receives the sound wave that is then displayed on the screen of the sonar unit. In theory the sound produced by the transducer radiates out like an upside down ice cream cone, widening as it gets deeper. For most freshwater fishing applications a 20-degree transducer works just great. Wider cone angles will show more bottom area but detail is lost. Smaller cone angles will show greater detail, but only a very small area of the bottom. As a general rule of thumb a 20 degree cone angle is showing an area with a diameter about 1/3 the depth of the water. In 30 feet of water the area you view on your sonar screen is only about 10 feet in diameter!

Split Screen Zoom-To see even more detail on your sonar; buy a unit that has split screen zoom. This feature lets you "zoom in" on a particular part of the water column for greater detail while still allowing ½ of the screen to show a reading of the complete water column from top to bottom.

Alarms-One feature often overlooked by sonar buyers is the presence of alarms on a unit. Two different alarms are available and strongly recommended. First is the shallow alarm, which goes off when the boat enters into water shallower then a user preset depth. Second is the deep alarm that goes off when the boat enters water deeper then a user set depth.

Depth Range, Sensitivity and Grayline- All good sonar units have these 3 features and they are grouped together because on a good sonar they all have the same characteristics-they can be set be the user. Most cheaper sonar units have set depth ranges such as 0-10,0-20,0-60 etc. These ranges make the user settle for a poor reading as many times pixels are wasted looking at too much area deeper then the actual lake bottom. The better units allow the user to set any top and bottom depth as long as they are at least 5 feet apart. Sensitivity and Grayline also need to be user selectable. Most low quality units only have 4 settings –Off, Low, Medium and High.

As you can see buying the proper sonar unit takes a little homework. The past 5 years has seen a dramatic rise in sonar quality and a lowering of sonar prices, but a top quality unit is still a pricey investment. Choose your next unit using the above guidelines and you will have an invaluable fishing tool for many years to come.