Fishfinder Buying Guide

Mark Griffiths Mark Griffiths

Roaming a lake in your boat fishing at random locations often results in disappointment. Adding a fishfinder to your fishing arsenal greatly increases your chances of having an enjoyable time on the water.

Fishfinder Buying Guide

From basic fishfinder models under $100 to elaborate color display, GPS enhanced, and 3D readout versions, eBay is sure to have a listing for a type that will fit your fishing needs.

Fishfinder Uses

Fishfinders, also called depth finders, are an important tool for the fisherman. This device sends a sound wave into the water by way of the transducer. The sound wave reflects off an object such as a fish, or the bottom, and is detected by the transducer also. These echoes are interpreted by the fishfinder and sent to the display. This simple process can provide you with a wealth of information about the unseen region below the water's surface.

The typical fishfinder can reveal a wide range of underwater items. Single fish, schools of fish, bottom composition (soft, rocky), thermoclines (a large change in water temperature), weeds, many types of structure (stumps, wrecks, drop offs, mounds), and much more. Fishfinders with added features can also provide surface water temperature, speed, barometric pressure, and location (GPS).

Choose Your Fishfinder Equipment

Fishfinder manufacturers make a range of models to suit the far ranging needs of fisherman. You can spend less than $100 or more than $2000 depending on the degree of features you require.

Your individual fishing style will dictate what fishfinder features you should select.

The two major decisions you'll have to make are regarding the transducer and display.


  • Do you need wide beam, narrow beam, both, or specialized beam?

    The transducer sends down a sound wave usually in the shape of a cone. Think of an ice cream cone with the pointed end attached to your transducer and the open, round end, extending down into the water all the way to the bottom. A narrow beam usually has an angle of about 20 degrees. If you are in 20 feet of water, that would translate into a circle on the bottom about 7 feet across. If you had a wide beam transducer (usually about 60 degree angle), it would form a circle on the bottom 22 feet across. Your fishfinder can only give you information on objects that are within the cone. The wider beam covers more area under water and can locate more fish within its larger cone. The drawback of the wider beam is that it looses strength much quicker. Because of this, it cannot go as deep as the narrow cone. The narrow cone can penetrate water much deeper and even in shallower water; can give more information on the composition of the bottom (mud, weed, rock, etc.)

    The best of both worlds is the dual beam (also called dual frequency), that combines both features into one transducer.

    There are also specialized transducers. Some have multiple beams (4 or more) that cover a very large area underwater and can create a 3D image on the display. There are also side beam transducers that actually shoot their beam to the sides to increase the search area for fish.

  • How will you mount your transducer?

    The transducer that is included with the fishfinder you purchase will probably be one that attaches to the transom of your boat. If you have a single hulled fiberglass boat, you can usually mount the transducer to the inside bottom of your boat with epoxy. This is referred to as,"shooting through the hull" mounting.


  • It's all about pixels!

    The more pixels you get, the more detail you'll see, and the more money you'll spend. A pixel is the smallest dot (or square) on the display screen. A low priced model may list their display as 160V x 132H. That would be a display that is 160 pixels vertically and 132 pixels horizontally. But even with this low priced model, that amounts to a screen with 21,120 dots on it. A higher priced fishfinder may have 640V x 320H which would squeeze about 10 times more dots on the screen giving you better resolution.

    Each pixel can have varying degrees of black. Low priced fishfinders may have no greyscale at all or a 4 level grey scale. Higher priced models may have 12 levels of grey for each pixel.

    Color has its price. You will pay more for a color display. You will also pay in the amount of resolution you get. The typical color display will cost more and have fewer pixels than a similar black and white model. But instead of 12 levels of grey, each pixel may have up to 256 color choices.

    Every eBay auction for a fishfinder should have a good screenshot of the fishfinder's display. You'll have to judge for yourself whether you want color or black and white, and what degree of resolution you require.

  • Other display features: There is usually a lengthy list of display features for a fishfinder. You'll have to decide if any of them are important to you.


The power of the fishfinder determines its maximum usable depth. A 100 watts of power can reach up to 600 feet. While a 500 watt model that can go to 1500 feet. Salt water absorbs more energy so higher power models are preferred.


Portable fishfinders are entirely self-contained. The fishfinder comes in its own carrying case with battery power supply. The transducer is attached to the transom by way of a suction cup.


GPS will be discussed separately below, but is a major decision in the buying process.


The fishfinder manufacturers that you see most often listed on eBay are Eagle, Garmin, Humminbird, and Lowrance. Other manufacturers include Bottomline, Furuno, Interphase, Navman, PinPoint, Raymarine, Simrad, and Sitex.

Miscellaneous Features

These are all the extra features manufacturers attach to their fishfinders to make them better or different than their competition. They include things like: backlit screen, adjustable display speed, freeze frame, and many more.

Add GPS for the Ultimate Fishing Tool

The Global Positioning System (GPS) uses information it receives from satellites to calculate your exact position. Unlike satellite TV which charges a subscription fee, the GPS radio signal is free for everyone to use.

Affordable GPS is now one of those "must have" fishing items. Having one unit on your console that is both a fishfinder and a GPS is economical and a real space saver. Just like fishfinder features, the GPS component can range from basic features to elaborate detail with color background maps.

The three main reasons you should have GPS

  • Saving hot spot locations: This is the biggest feature for the fisherman. The ability to find a hot fishing spot, mark it on your GPS and be able to return to the same spot in the future is a powerful feature. Most GPS capable fishfinders give you the ability to mark hundreds or thousands of spots (called waypoints) for future use.

    Example: In the middle of Lake Erie are some sunken train cars. They were pushed off of a barge to dispose of them decades ago. Walleye stick to this structure like a magnet. Finding this spot out in open water without a fishfinder and GPS is impossible. If you have just a fishfinder, you may be able to find it, but it takes a lot of time zigzagging around until to happen to go over it. This wastes a lot of valuable fishing time. With a GPS, your fishfinder GPS combo gives you a heading and a distance that will put you right on top of it with no wasted time.

    How Close Will a GPS Get You? Your basic GPS will get you within about 50 feet of your waypoint. Most GPS units now come with WAAS. This enhancement adds additional accuracy to your location and can get you within 10 feet of your waypoint every time.

  • Navigation: If you need to refer to charts to navigate your way, you should select a fishfinder GPS combo unit with background maps and charts included.
  • Safety: When you start your day of fishing, you mark your starting point with a waypoint on your GPS. You are now free to fish wherever you choose with the confidence that your GPS can point you home with ease. You may have followed a random path of fishing locations throughout the day, lost sight of land, or severe weather has rolled in limiting your visibility and your GPS can tell you exactly what heading to go and how far away "home" is.

    New marine radios have a feature that allows you to connect your GPS fishfinder combo unit to your marine radio. Should you have to activate your radio's DSC distress feature, it can transmit your exact location to get help to you the quickest.

GPS Functional or GPS Ready? Some fishfinders are GPS functional right out of the box. Some fishfinders are GPS "ready". They have the GPS software and functions built into the unit already, but require you to purchase something extra (usually the antenna/receiver) to activate the GPS features.

Fishfinder Accessories

Every fishfinder is ready to use right out of the box. The transducer, cables, and mounting hardware are included. But you may desire some added features to improve its usefulness.

Some of the most common accessories are:

  • Transducer replacement: The transducer that comes with your fishfinder is usually the only one you will ever need. All manufacturers offer alternate transducers.
  • Speed sensor: If you don't have GPS, adding a speed sensor can be quite helpful if your fishing method includes trolling.

Search Tips

  • Search for fishfinder, fish finder, & depth finder to find the most listing.
  • Humminbird has no "G"

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