First; a quick understanding of how a fishfinder works.

All fishfinders use a sound wave sent through the water called "sonar". The sound wave increases in diameter as it travels through the water forming a cone. When the sonar encounters a solid object within the cone it bounces back to the transducer and the shape of the object is recorded on the screen at the depth calculated by the time lapsed between sending the signal and receiving the bounce back. Remember; the deeper the water the larger the cone becomes.

Second Decide how much you want to spend and then double it. Now that the budget is set, lets see what we can learn to try to stay in it and get the right fishfinder for the type fishing you plan to do.

Having set the budget there are only five more parameters you really need to consider. Or maybe 6 or 7.

DEPTH

First: Be aware that the depth ratings advertised with the unit are for clean fresh water unless otherwise stated. Salt water and murky fresh water will reduce the effectiveness in the deeper water ranges. The more the unit costs the better it will penetrate deeper water.

Recommendation: Buy a unit rated for at least 10% more depth than you plan to fish.

TRANSDUCER

Not all fishfinders come with a transducer. Check the included accessories before purchase. There are two types of transducers and good reason to choose one, the other or a combination of both. Single frequency transducers are best for inland lakes and shallow coastal waters. Dual frequency transducers are used for offshore deep water fishing as the second frequency is a high frequency which is what will show you fish in a smaller cone. An example would be; a 50 kHz may have a 4 degree cone to reach deep and still give a good sized view of the bottom where a 200 kHz might have a 20 degree cone so that it can also give a large enough view of the bottom in shallow water. You have to be aware of which you are using because either on will fill the screen but only the right one will give accurate information.

Now comes the installation. Are you going to use the fishfinder on only one boat or do you want to be able to use it on a buddies boat? Do you want a through hull installation for the best clarity or will a transom mount be sufficient?

There are several manufacturers of portable fishfinders with portable single frequency transducers. They are generally intended for small boats on inland lakes, streams and rivers.

Transom mount transducers are easier to install and generally less expensive. They come in single and dual frequency models. Transom mounted transducer are in water that is quite disturbed by a fast moving boat and usually are not effective at much more than 10 knots.

Through hull transducers are by far the best when it comes to clarity and performance. Of coarse you have to have room for another hole in the hull and a need for high speed bottom reading to make them worth the difference.

Recommendation: If you are going offshore or even in deep freshwater, consider using a through hull transducer with dual frequency for greater clarity and more accurate depth to fish readings and still be able to get a good bottom picture in shallower water.

If you are using a small boat and are not concerned with high speed fish finding, use a transom mount or portable unit. Save money, put fuel in the boat!

POWER

In general; the more power you can get for the money the better off you will be. If compared to a unit of all equal amenities the less expensive unit will have less power. The power decreases clarity and speed of returned echos.

Recommendation: When comparing units consider the power rating as the highest weighted factor.

DISPLAY RESOLUTION

Here again, the higher the resolution the better the picture you will get and the more you will pay. A color screen is much easier to see in bright sun light.

Recommendation: Compare the resolution to same price units and choose the higher resolution unit. We like a minimum of 320x240 but prefer 480x480.

DISPLAY AND UNIT SIZE

Bigger is better! But if it doesn't fit were you want it then it's no longer better. Measure the space available for installation of the display unit and find one to fit within that limit. There are some really powerful fishfinders with as small as 4" diagonal screens. Of coarse, the larger the screen the larger the price tag.

FISHFINDER REVIEWS

They're all biased! They have been written by a guy who hasn't used everyone of them and probably either works for a manufacturer or has a store that sells his favored review. Do your home work. Then go to the fishfinder review page on eFishBox.com and make the comparisons. The site has all the specifications and abilities of all the major brand fish finders.