Depth/Fish Finders

December 11th, 2009

by Capt. Gus Gustafson

This year’s Sonar/GPS units have brilliant display screens and easy to use keypads. New features include side-imaging, wider bottom coverage, and enhanced target returns. Broadband high definition technology makes viewing easier than ever to interpret. Mapping options include 3-D viewing and contour shading. If you are new to marine electronics, you might consider a few other options before deciding which unit to buy.

• Will the unit be used as a depth finder only or as a combination depth/fish finder?
• Will the cost justify the amount of usage and the perceived results?
• Will the unit fit the allotted space on the boat console?
• What about pixel count, screen size, power ratings, and color or black and white?
• What about service?

If the primary use of the electronic instrument is to be a depth finder, an inexpensive-to-medium priced unit will do the job. When properly installed, a depth finder in the $75 range will provide constant bottom readings at most speeds without interference. A useful feature on any depth finder is a (shallow-deep) water alarm.

The screen of a depth finder consists of small squares or dots known as pixels. The more pixels per square inch, the clearer the image. Vertical pixels separate fish from fish, fish from bait and fish from structure. The higher the vertical pixel count, the clearer the image. A high horizontal pixel count also allows for a wide screen and superior viewing when the unit is used in the split screen mode. A minimum of 160 vertical pixels is required to clearly distinguish fish suspended just off the bottom in 30 feet of water. Deluxe units have vertical pixel counts of over 600 and horizontal counts of 800.

Black and white or color? Black and white is functional and is the least expensive option. Color enhances the view and allows the images to seemingly jump off the screen. A color unit is considerably more expensive. Is it worth the difference? Most fishermen believe that it is.

How much power? The more power a unit has, the deeper it can read underwater objects. Power is measured several ways. All are confusing, to say the least. One common measure is known as peak-to-peak. Peak-to-peak is normally used to describe power output at the sonar transmitter. The peak-to-peak comparison is used by most manufactures. A unit with 800 watts of P-to-P power can read bottom depths to 600 feet. Peak-to-peak power is similar to a car’s horsepower rating. Consider a minimum of 1500 watts of peak-to-peak power.

The major electronic manufacturers (Garmin, Lowrance, Hummingbird), pride themselves in repairing or replacing a non-working unit in a matter of days, not weeks. The procedure is simple. Call the 800 number to contact a technician. Many times the issue can be resolved over the phone. If not, you will be given a repair authorization number and made aware if the age of the unit has exceeded the warranty period and if any charges are due. As a rule, you will only need to return the electronic unit itself. The brackets, power cords and transducer can remain on the boat.

Before buying any depth finder, fish with someone who has a unit similar to the one you are interested in purchasing. If that is not possible, ask a tackle store salesperson to show you how the display unit works in the simulator mode. Several company web sites can also walk you through the comparison process. Downloadable PC-based software applications that simulate the use of a unit are also available on line.

Visit Capt. Gus at, email him at or call 704-617-6812.