Basic Fishfinder Tutorial

[Fishers of Men]

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.
Transducer
• 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.
Display
• 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.
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.
Power
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
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.

to be continued...

More continued:

All fishfinders are not created equal.
Although features often dictate the quality level of the overall unit, some will be equipped with stronger or weaker outputs, single or dual frequency capabilities, and several other different features.
The first detail to look for is the unit's power rating. Like stereos, it may be given in one of two ways: peak-to-peak and RMS.

Completely ignore the peak-to-peak number, as it tells you little about the unit's actual performance.

A relatively-inexpensive unit that puts out 300 watts RMS, for example, will occasionally be listed as a 2,400-watt unit in marketing hype.
Which figure seems more realistic to you?

Some units feature buttons, some dials, some knobs, some hot-keys and some have a combination of controls.

Before getting into wattage and what it means, we have to repeat and note that transducer size has a huge bearing on fishfinder performance.
In fact, doubling the transducer size actually has the same effect as quadrupling the output power.

The larger the transducer, the more focused its beam – think of the ever-widening pings it emits as if it were a flashlight beam set to spotlight, instead of floodlight. So, a machine pushing 200 watts through an eight-inch transducer will see just as deep as a fishfinder pushing 800 watts through a two-inch transducer.

That said, the majority of the combo units you're likely to see on the open market will come with a two- or three-inch transom-mounted transducer, and other transducers will have to be ordered.
With these common transducers, a 100- to 300-watt machine will do the trick for bay and inland boaters who don't need to see the bottom in water any deeper than 150 feet to 200 feet.

Three hundred to 500-watt machines will hit bottom just fine in waters down to about 500 feet, and 600- to 1,000-watt machines are only necessary if you want to get bottom readings in waters off the Continental Shelf.

Wait a sec – there's one more variable that needs to be discussed: frequency.
This, too, will effect depth capabilities and detail, as well.

Most units run on 200 kilohertz, which is a great shallow-water frequency.
In water more than 500 feet deep, lower frequencies like 50 kilohertz often work better.

Just about all units come with high frequency capability, but if a unit you're looking at boasts dual frequencies and can also ping at the low frequency levels, score it extra points if you're interested in seeing the bottom in very deep waters.

to be continued...

Fish Finder Tuning Gain
The key to getting the most information from any depth finder is in learning how to peak the transducer.
Too much power will fill the screen with clutter and overpower the machine.

Too little power will not show such important underwater features as thermoclines, schools of baitfish and even game fish.

Understand the difference between Manual/Auto Gain.
The most important thing to understand is the use of the gain controls.
These settings have a significant affect on the performance of the fishfinder.
The manual gain setting is very much as it appears. The gain of the receiver circuit can be set to a fixed value and remains fixed at that value until the user changes it.

The Auto Gain setting is very different.
In Auto Gain the software continually varies the gain of the receiver section to match the environment and the level of the return signal.
In other words the software continues to alter the receiver gain to obtain the best possible return signal.
The purpose of the Auto gain setting is to control the displayed width of the bottom.
A low Auto gain setting results in the bottom contour appearing narrow or thin.
A high Auto gain setting causes the bottom to appear wide or thick on the display.

It is worthwhile to experiment with different Manual gain settings.
This single setting has the largest effect on the performance of the Fishfinder.

There is always a conflict between low and high manual gain settings.
Lower Manual gain settings usually produce a better "fish" image.
With the higher Manual gain settings the fish images may appear corrupted and look more like a 'blob' on the screen rather that the usual arches.

This is particularly important when looking for fish near the bottom.
With a higher Manual gain setting fish near the bottom will start to blend in with the bottom making them hard to recognize.

The gain or sensitivity knob controls the signal power output of the unit.

The first step in peaking the transducer is turn off any automatic gain controls the unit might have and go to manual control of the power output.

Now, select a deeper depth range setting than the actual bottom depth.
For example:
If you're in 200 feet of water, set the depth range for 600 feet. If you're working shallower, say in 40 feet, set the range for 160 feet.
Tripling the actual depth is necessary for this operation.

Start to turn up the power gain.
First, you'll see the bottom, which only makes sense since the harder and larger the object, the stronger the return signal.

The ocean or lake floor provides a solid return.
Continue to increase the gain until you get a "second echo."

The second echo is nothing more than the return signal bouncing off the bottom once and then having enough energy to make the trip back to the bottom and up again to the transducer.
The second echo shows up on the screen as a second bottom reading at double the depth of the real bottom.
The screen will now be showing a bottom reading at say 25 feet and another bottom reading at 50 feet.
Now you can understand why you need to have the depth range set at triple the actual depth to accomplish this procedure.

Once you have a strong second echo reading, you can return the unit back to the normal depth setting for actual fishing conditions.

You have maximized the power being sent through the transducer so you will be able to acquire the most information from the depth finder screen.
You will begin to notice things on the screen that you were missing on lower power settings or on an automatic sensitivity mode.
You'll mark fish, bait, temperature changes in the water column and more.
But, you must realize that once you peak the transducer for a specific depth range, you have only about a 20 percent window in actual depth before you have to repeat the procedure.
In other words, if you peak the unit while fishing in 200 feet of water and you begin moving into deeper water, say into 300 feet, you will have to repeat the procedure for the deeper water.

to be cont with sensitivity...

[COmmodore 64]

Van, thanks for these write-ups. Could you explain the process of tuning the gain/sensitivity? Any tips?

[fishingguy]

One thing I have learned is I can change the upper and lower ranges on my sounder. If I am fishing in 60' of water, I can set my sounder up to see only the area between 20' to 50'. What this does is double the pixels for that area. I really have no interest in what's above 20' or below 50', so why waste the pixels on it. It's a lot better than the zoom feature, zoom doesn't increase the # of pixels it just magnifies, and to some extent distorts them.

[Fishers of Men]

Originally Posted by COmmodore 64

Van, thanks for these write-ups. Could you explain the process of tuning the gain/sensitivity? Any tips?

Did you get the pro fish II or the III? I cant remember.
I sent your dad a deer head customer back in season. He had to do his magic, the guy ringed it's neck on the drag out.

You going to be at Ravenna Marine on the 28th? I am going to do a Nite bite seminar at 3:30...Hope they are cookin all that fish up again lol.

I will put another thread up, no I will add it to the finder thread, when I come back in tonite on tweeking gains and sensitivity issues.
Probably be better that way so that there are reference threads for future questions others may have and might keep down repetition.

I didn't mean to commodeer this thread, just wanted to get some basic info up to get it going and then everyone would have something to work from or go off of.

[COmmodore 64]

I went with the Pro-Fish II.

It seems to lose the bottom every so often...very frequently in shallow water that is less than 10 feet which is somewhat disconcerting since that's when you need it most from a depth-sounding standpoint.

[Fishers of Men]

Originally Posted by COmmodore 64

I went with the Pro-Fish II.

It seems to lose the bottom every so often...very frequently in shallow water that is less than 10 feet which is somewhat disconcerting since that's when you need it most from a depth-sounding standpoint.

It's something simple but could be one or more of many things.

I continued the first post about "gain".

Could be:
Gain,
Your transducer angle, transducer depth, verses speed, transducer/hull position, causes for air bubbles, transducer cavitation (correct offset), difference between water level and transducer level, change in boat load?
Do you have the shallow water alarm feature on?
Increase sensitivity a little at a time.
Try turning the noise filter off.
Try setting the contrast a lil higher.
Low voltage will cause this.
I have a feeling you are getting air under it.
More than likely the transducer needs adjusted and/or settings played with.
Also,
Dead Zone is the area within the transducers cone of sound that is blind to you.
The wider the beam angle the greater the possible dead zone.
The sonar will mark bottom as the nearest distance it sees.
If you are fishing or going over a slope it may see the high side of the slope, at the edge of the cone, and mark that as bottom.
It may not show the lower slope or fish in that area.
The fish that are hanging on the bottom in the center of the cone will be invisible to you because they are actually within the bottom signal on your depth finder.
A narrower beam angle will reduce this effect.
This again will be playing with the sensitivity to maximize returns.

[fishingguy]

COmmodore, I got a lowrance and it pretty much sucks in water less than 8'. If I need it to be accurate at that depth I will switch to flasher mode. I think it's a bit easier to read and a quicker display. Just my thought, could be wrong. Very rarely do I ever run into the situation. The only time it would come in play is when I am in an area that I am not familiar with, leaving and returning to the ramp.

[Fishers of Men]

This unit:
Displays depth from 5' to 1500' in 5-foot increments.
Also displays amount and diameter of bottom area being searched.
Surface Signal Processing eliminates unwanted clutter.
Independent depth settings, Upper/Lower, allow full high-speed sampling and maximum "paper chart" resolution...And more.
Actual depth capability of a depth sounder depends on quality of installation, type of bottom, salinity of water, etc.
This is more reasons why I said It's an adjustment issue.

thought of something else, what selectable beam are you running in shallow? 15° or 40°

[COmmodore 64]

I've always use the wider beam..40-degrees.

The shallow bottom readings are important for our fishing trip to the Thousand Island region where we are often fishing or passing through water <8 feet deep. It's crazy up there with the rocks and stuff.

[Fishers of Men]

You should be able to dial that in to the foot with no problem.
Double check the mounting and everything I mentioned.

[cjbrown]

Originally Posted by fishingguy

COmmodore, I got a lowrance and it pretty much sucks in water less than 8'. If I need it to be accurate at that depth I will switch to flasher mode. I think it's a bit easier to read and a quicker display. Just my thought, could be wrong. Very rarely do I ever run into the situation. The only time it would come in play is when I am in an area that I am not familiar with, leaving and returning to the ramp.

Do you leave your unit in auto mode when in shallow water? I've found if I turn my ping speed down and the sensitivity in less than 10 ft of water it's accurate with nice detail.

[COmmodore 64]

Originally Posted by cjbrown

Do you leave your unit in auto mode when in shallow water? I've found if I turn my ping speed down and the sensitivity in less than 10 ft of water it's accurate with nice detail.

I will try this too, thanks!

[fishingguy]

I usually never have the unit in auto mode. But, your right, I should be turning down the sensitivity. I'll mess with it this year, if I can remember. Fish Erie mostly and don't normally need the shallow water readouts. Actually, I usually eliminate the top 10' or 20' when I am out deep. Don't want to waste the pixels on water that I am not interested in.