Eagle SILENT 101 INSTALLATION INSTRUCTIONS
sound ends at the bottom. But an echo is also returnedfrom
any objectbetweenthe transducer and the bottom.
As you move away from shore on a deep lake, the bottomsignal
will gradually move around the dial until it reaches zero. Ifthe
dial is calibrated to a depth of
100 feet, the water is 100 feet deep. Continue further, and the bottom signal will start around again.Add whatever figure it showsto 100 to get the correct
depth. OtherEagle modelshave dual rangesthat allow you to
change to a deeperscalewhen you go deeper than 100 feet.
SIGNAL INTERPRETATION
BecauseyourEagle is both ex- tremely sensitive and powerful,
it can give you an accurate pic- ture of the kind of bottom over
which your boat is passing. A
bottom offirm sand, gravel, shell, or hard clay returnsa
bright,fairly wide signal. Ifyou are traveling over such a bottom
and the signal weakens,it means thatyou have moved over
a soft mud bottom. A soft bottom absorbs the sound waves and re-
turns a weak signal. In this case,
simply turn up the sensitivity to get a good bottom reading.
A level bottomwith scattered rocks returnstheusual bottom
signal — plussecondary signals both above and belowit. This is
caused by the differentdistances the sound waves travel. Those
that go straightdown, hit a rock,
and come back indicate,cor- rectly,that the top ofthe rock is
above the level of the bottom.
But the sound wavesthat hit a
rock toward the outer edge of the |
DETECTINGA SMOOTH BOTTOM |
cone ofsound wavesand are re- |
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flected back to the transducer |
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travel further. Consequently, |
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their signals appear below the |
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bottomsignal. |
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A smooth bottomof solid rock returns a wide, bright signal.
Broken rock ofvarious sizes
sends back an even wider one, with occasional flashes above
and belowthe level of the true
bottom, though these signa]s aren't so distinct as the onesre-
turned by scattered rocks on a smooth bottom.
Big rocks or stumps on a smooth bottom send back signals above the level of a smoothbottom,the distance dependingon their height. Ifyou watch as you ap- proach a post or a tree, however, you will often see the signal climb up, then descendthe other
side as you continue.
A steep slope returns a wide sig-
nal, the steeper the wider, with the signal returnedfrom a high
underwater cliiibeing the widest. The sure proofofa
drop-offis the sudden change of
the regular depth signal to a wide one, then back.tothe usual width, but either more shallow
or deeper as the boat movespast.
Brush will return flashes of
varying heights above the bot- tom signal. Weeds also tie in
with the bottom,although they return weakersignals than brushor tree limbs. In most
lakes, weedsdon't grow in water more than 12 or 15 feet deep be-
cause ofthe lack of sunlight.
Weeds make a greatmany thin, pale signals on the dial.
0
I Gravelor Hard Ciay
Ag. 14
The nicest bottoms
to survey with your
EAGLE are those that return a clear, bright
signal, with no spikes either above or below
it from scattered rocks.
This is the easiest bot-
tom signal of all to read and fish at any depthabove it show up
plainly on the dial.
Nothingis more
gratifying than to find a big schoolof
largemouth bass over clean gravel or wall-
eyes over a smooth sandbar— places that
these two popular fish like and that are easy to fish by the bottom-
bumping technique.
It is easy to get mul-
tiple signals on the dial from bottoms of
this type. Ifyou are over water20 feet
deep, for example, and turn up the gain you'll get signals at 20and
40 feet.
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WEAK SIGNALINDICATES GAINTOO LOW
Fig. 12
The sensitivity con- trol on your EAGLE
might be comparedto the volumeon a radio.
'ibm the sensitivity knob to the right and
you increase the re-
ceiver sensitivity; turn it to the left and you reduceit. This feature is provided so thatyou
can use your EAGLE
over both deep and shallow waterand you
should always adjust the gain so that a
bright bottomsignal showson the dial, re-
gardless of depth. If you fail to do so and
have only a faint bot-
tom signal the dial will fail to show fish
in the waterbetween
the transducer and the bottom.This condition is shown in the draw-
ing above — the fish are there but they aren't shown on the
dial becausethe gain
is set too low.
Fish, 17 ft.
Depth, 35 ft.
constant speed behind the dial on a disc drivenby an accurately governed motor. The bulb is
lighted every time the transmit- ter fires. This providesa visual
referencepoint on the dial which is used as a starting point to
measure depth, and as an indi- cator that the depth sounder is
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on. Even though the neon bulb |
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flashes, it happens so.often that |
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the humaneye sees it as a |
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nearlyconstant light. |
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The bulb also flashes at the |
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point on the dial that indicates |
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the depth.Fhe point is indicated |
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bythe length of time it takes the |
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sound waves to reachthe bottom |
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and return. In addition, echoes |
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ieturnedfrom any objectin the |
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vater between the surface and |
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bottom fire the bulb, too. Since |
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these echoes are also timed, they |
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showthe exact depthof any fish |
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— or any numberof fish — in |
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the water. And because the |
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sound Waves from the transducer |
Fig. 15 |
go down into the waterin a nar- |
row cone angle, they tell, within a matter ofa fewfeet, the fish's
location as well as the depth.
At a depth of10 feet, the cone coversa circle that is approxi-
mately one foot in diameter; at
15 feet it is two feet wide, at 20 feet, threefeet wide, the cone
diameter is four feet wide. Re- gardless ofdepth, the cone of
ii
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ing to insure that they see all the underwater detail as well as
fish.
Depths greaterthan 100 feet can alsobe measured on the Eagle.
For instance,as the waterdepth goesfrom 90 feet to 110 feet, you will see the bottomsignal onthe
dial move past the "zero" signal to the 10-footmarlc on the outer
scale. Thus, on the second revo- lution, depths of100 to 200 feet
may be read by adding 100 feet to the readingon the dial.
Ifin doubt as to depth, turn unit offuntil scan disc stops. Thrn unitback on and watch to see if
bottom signalcompletes one rev- olution before stopping. Ifit does,you are at the depth shown plus 100 feet. Ifthe signal
travels around the dial two
times, you will be at the depth shown plus 200 feet.
HOW TO USE YOUR EAGLE DEPTH
SOUNDER
'rhe word "Sonar" is an abbrevi- ation ofSound, Navigation, and
Ranging. It was developed dur- ing World War II as a means of
trackingenemy submarines. Sound travels at approximately
4,800feet per secondthrough water as comparedto approxi-
mately 1,100 feet per second through air.
PRINCIPLE OF SONAR
)flfl)flflflflflflfl)flfl
((((( (((N
HARD CLAY, SAND, GRAVEL,SHELL BOTTOMS
Somefish, including
bass, catfish, walleyes, and crappies,occa-
sionally lie right on the bottom.Even here
the EAGLEwill show
them as you pass over, providedthe bottom is
smooth sand, shell, or
gravel. Signals will
appear on the dial both above and below
SIGNAL SENT BY LOCATOR BOUNCES BACK 'FRoM
TARGET. TIME LAPSE INDICATES DISTANCE TO TARGET
Fig. 11
transmittedinto the water. When this wave strikesan ob-
ject, it rebounds. Since the speed of sound throughwateris known, the time lapse between
the transmittedsignal and the received echo can be measured and the distance to the object determined.
The Eagle depth sounder trans- |
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mits a highfrequencysound |
Sandbottom |
wave (whichis inaudible to fish |
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as well as humans) through the |
4. |
water. At the same time, a high |
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intensity neon bulb whirls at a |
Fig. 16 |
the clear bottomsig- nal, just the same as
over a rocky bottom. The reason forthis
is that the signal re-
turning from a fish near the centerof the
cone of sound doesn't
travel so far as the
signalthat hits a fish near the outer edge of
sequently,the signal from the fish in the
middle showsabove the bottom while the
signalfrom thefish near the edge shows
below the bottom.
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