This month we're looking at some of the basic questions which some people ask and most people want – a general overview of the very basic fishfinder operation.

What am I looking at?


Fish finders tell you the distance from the transducer to the fish, weed and bottom below. The right hand side of the screen is what is directly below the transducer, right now. Sometimes this is also shown on an “A scope” which shows this as a larger bar. Everything to the left of this is history, getting further back toward the right.

What do fish look like on my fishfinder?

The general rule of thumb is – If a mark is not attached to the bottom (seaweed) or attached to the top (surface noise or turbulence) then its fish (or a plastic bag!). Generally schools of bait fish will appear as large blobs of softer colours, while individual fish will appear as lines of stronger colour.

Why can't I see fish arches on my sounder

A common misconception about fish finders is that fish will appear as arches. This is not always the case, and in particular
is effected by the beam width of the transducer, and the speed of the boat. Unfortunately manufacturers don't help the situation by making sure their demonstration modes are covered in pretty fish arches!

I loose the picture as soon as I start moving. Is there something wrong with my fish finder?

Probably not. The ability for the fish finder to get a good picture while the boat is moving at a reasonable pace is only effected by how the transducer is mounted. The worlds best fish finder wouldn't be able to get a good picture at speed if the transducer was mounted incorrectly. Good transducers have detailed installation instructions which clearly show the best way to mount them.

snapperWhat is “Gain”?

Gain amplifies the received echos to levels which can be clearly seen on the screen. Think of gain like the light in a very dark room – if you turn on a dim light you might miss different items in the room, if the light is too bright, it will be too bright and you will be blinded. Too little gain and you will not see the fish on the screen, too much and the whole screen is covered in echos and you won't be able to tell what's what. If you are new to fish finders, it is probably best to leave the gain on auto. Once you get the hang of it, you will get much better performance on manual.

Should I turn off the sounder while fishing?

Although the frequencies used by the fish finder are much higher than what fish and humans can hear, anyone who has gone swimming under a transducer doing its thing will attest that it is not a very nice experience. So we recommend that if you are anchored and fishing it is probably a good idea to turn the sounder off.

Is a colour sounder better than black & white?

Yes. Grey scale sounders can distinguish the returned echo into 4-8 different shades of grey while colour sounders can split the echo into literally hundreds of different shades, which means colour sounders will give a much truer representation of what's beneath.

How deep will my unit go?

Most modern sounders (less than 5 years old) will be able to reach about 1/3 the power output in depth. If the unit is 100W, it should reach 33M. If it is 600W then it will reach 200M. These numbers will be greatly effected by sea conditions and transducer placement however and certain, more expensive units will give much greater depth performance.

Should I use 50kHz or 200kHz?

The simplified answer is: 200kHz should be used in shallow water while 50kHz (or 77kHz depending on unit) is better in deep water. There are issues with cone angle which are beyond this very basic article, but if you are in doubt, use both! Most units will have the ability to split frequency, which can be a good display to use.

Have you got a question we didn't cover??? leave it below and we'll make sure we answer it!