This article was copied out of a magazine...the unfortunate thing is I do not remember what mag. or who was the author
Just rememeber that any reference concerning color can be applied with gray scale.
Far
too often, I've had customers and fellow anglers tell me that their color
sounders were not working properly. The
majority of the time, once I step on board I find the only problem is operator
error, or more to the point, operator ignorance.
My own fishing experience with sonar started with a Gemtronics 1202S
Curve-linear chart flasher/recorder, a very high tech unit when I purchased back
in 1976, but a real dinosaur by today's standards.
At
the start of each fishing day, I would get on the boat, turn it on and set the
sensitivity level so it would produce a very precise bottom line on the chart
paper at the dock. Upon getting to
the offshore grounds, at that time offshore for me wasn't much more than six
miles off the beach, I would look at the machine and not see a damn thing, no
bottom reading whatsoever. Even
when I was catching fish, I wasn't reading them on the recorder and it was
frustrating. I cursed out the
electronics dealer that sold it to the installer the manufacturer and me.
I'd
send it out for repairs and the manufacturer would send it back to me with a
note indicating they found nothing wrong with the unit and I would repeat the
scenario again the next trip out. This
went on for two months, back and forth, but all I really needed was a course in
the unit's operation. It became
obvious that I was the problem, not the machine.
The
discount house I purchased the unit from was useless after the sale.
The installer, although he did a fine job on both the transducer and unit
installation, was not a fisherman and also offered little help with using it for
fishing. It wasn't until I actually
sat down and studied the manual, which appeared more like an ancient text in
some dead language that I realize how little I knew about the workings of a fish
finder.
I
later found that the unit was capable of providing me with far more information
than I ever imagined. This is the
case with many fishermen when it comes to this most basic piece of marine
electronics.
While
my job here is not to teach you depthfinder theory, I do need to teach some of
you the basics so you'll have a better idea of just how sonar operates.
Once you understand the basics, you will see a new world develop right in
front of your eyes from the same machine you thought was not performing properly
or needed to be repaired or replaced.
Basic
Depthfinder Operating Principles
A
depthfinder generates an electrical impulse within the unit, which is converted,
to mechanical energy in the form of sound waves in the transducer.
The sound waves are transmitted downward through a heavy medium (water),
where it bounces off objects and the signal is reflected back to the transducer.
The return signal is then picked up by the transducer and displayed as an
image on the unit's screen.
But
how does the unit determine water depth and the position of objects in the water
column between the transducer and the bottom? It's really very simple.
The depthfinder is actually a very precise clock that measures the time
it takes for the signal to travel from the transducer to the target and then
back to the transducer.
By
measuring the time from transmission to return, the unit calculates water depth
and displays it in the form of lighted LCD dots on an LCD screen model, as a
burn on chart paper in a paper recorder or as pixel illumination on a Cathode
Ray Tube (video screen) in an amber or color sounder. A depthfinder is actually not much more than a sound emitting
watch.
The
power of the signal being transmitted through the transducer is adjusted by
means of the sensitivity, gain or power control on the unit.
Power output is measured in watts and frequency of the output is measure
in kilohertz. When I turned on my old Gemtronics at the slip and it read
the bottom perfectly in eight feet of water, what I didn't understand was that
more power to gain was necessary for it to read accurately and clearly in 60 or
100 feet of water. Yeah, I felt
pretty dumb after I figured that one out and I hope that this article might help
you avoid feeling the same way
Now,
realize that the more powerful the signal you pump through the transducer, the
more information you will get back on the return signal, as long as you don't
over-power the unit. You can easily
increase the gain to the point that you totally fill the screen with clutter
from interference. We will cover
this in the section titled, "Peaking the Transducer."
Have
you ever noticed how some rooms have an echo when you speak?
Rooms that have an echo usually contain hardwood or tile floors, hard
surface walls and ceilings. Conversely,
in other rooms you nearly have to shout to be heard because sound doesn't carry
well and there is little or no reverberation or echo at all.
These rooms commonly have thick carpets on the floors, wallpaper, drapes
and acoustical tiles on the ceilings. The
difference is caused by the ability of the two rooms to reflect or absorb sound
and the correlation to depthfinder use will come into play when we discuss
bottom reading and how they differ between soft and hard bottom composition.
That will be covered under, "Understanding the Return Signal."
Last,
but not least, is understanding the different forms of structure and objects in
the water that your machine is capable of reading and distinguishing on the
screen. You'll be amazed by how
much information you can obtain when you learn how to "Interpret the
Screen."
What
is happening under your boat is some of the most valuable information you can
have when fishing. You can
determine whether there is a thermocline, underwater upwelling or pod of bait
down there with your depthfinder. You
can visualize an underwater sea mount, drop-off, reef or a wreck that could be
holding a school of tuna or that trophy blue marlin you seek.
Only
your depthfinder can provide this information when you're on the water and it is
important to practice using it properly. It
is a critical tool for serious and novice anglers alike, one that demands your
attention throughout a fishing trip. It has the potential to put more fish in the boat and the
greater your understanding and ability to make it work to its fullest, the more
beneficial it will be to your efforts.
If
you are a serious bluewater hunter, you really should have a color video
depthfinder, or color scope, to get the maximum amount of information on the
offshore grounds. The deeper the
waters you fish, the more important a color scope becomes. Yes, paper charter recorders can give you loads of valuable
information and many are capable of deep-water operation, but they do take more
getting used to and a greater degree of interpretation.
They are also getting hard to find, as most sonar manufacturers no longer
make paper graphs.
LCD
units have come a long way and are taking over where the paper machines left
off, but for deep water use on the offshore grounds, most lack sufficient power
and resolution to be a true deep water hunter's first choice.
For small boat, inshore tuna, shark and billfish, the LCD unit will do
the job well. Keep in mind that
much of the information we will discuss here can be applied to LCD and paper
chart recorders, too, so do not despair when you hear me mentioning color
sounders over and over. I have a
personal preference for color sounders because I fish larger boats and spend a
lot of time in the distant canyons of the Northeast, fishing waters that can run
as deep as 1,000 fathoms or more.
Color
sounders require operators with a Ph.D. in electronics and sound dynamics, or at
least that's what I thought when I bought my first one back in 1983.
It was as big as a small house, had more buttons, knobs, whistles and
bells than I thought I could ever master and all I knew once I turned it on was
the bottom was red or orange and the surface was a white line and everything in
between meant that I was on to something below the boat.
Exactly what, at that point, I didn't have the foggiest idea.
But, as I began to learn how to use the machine, all those pretty colors
began to take on meaning and the more meaning they acquired, the more
information I was getting from the unit.
That's
one of the beauties about fishing with a color sounder.
Unless you're color blind, it's almost impossible to not get more
information from them than other types of units.
You'll see why.
Peaking the Transducer
The
key to getting the most information from any depthfinder 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 gamefish.
The gain or sensitivity knob controls the signal power output of the
unit.
The
first step in peaking the transducer is [to] 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.
If you're in 300 feet of water set the depth range for 900 feet.
If you're working shallower, say in 60 feet, set the range for 180 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 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 250 feet and another bottom reading at 500 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
depthfinder 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, and temperature changes in the water column and more.
Do 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, if reading everything is your aim.
Understanding the Returned Signal
The
analogy of the two different rooms and how they reflect or absorb sound is
important to understanding signal return. Remember
that the room with that has hard floors, walls and ceiling bounces sound back
strong enough to cause an echo. Another
room with deep carpets, wallpaper and acoustical ceiling tiles has no echo,
simply because the soft materials in the room absorb a good portion of the sound
waves.
The
same holds true for signal returns to your transducer in water.
A soft bottom absorbs more signals and has a different appearance on the
screen than a hard bottom that provides a stronger return signal.
Peaking the transducer provides enough signal strength to compensate for
any absorption.
Once
you have your transducer peaked, select the range setting that will give you the
most information on the screen. Leave
some room at the bottom of the screen, which will be important for determining
bottom hardness, but try to set the bottom range so that you are pretty much
filling the screen with the water column from surface to bottom.
If
you're fishing in 180 feet set the machine for 200 feet, etc.
Hard bottom will reflect a sharp signal and will appear to be thicker on
the screen because of the strong signal. Soft
silt bottom will be represented as a thinner line on the screen because the soft
bottom material is absorbing more of the signal and providing a weaker return
signal.
Knowing
the bottom make up can be important, especially after a storm, when soft silt
bottoms do not hold baitfish as well as rock or gravel bottoms.
The silt that is stirred up into the water during a violent storm or when
particularly strong currents are present irritates the gills of baitfish, as
well as other fish. You will most
often find baitfish over hard bottom areas after such an occurrence.
Remember
that you've peaked the transducer and you are getting more of this type of
information on your machine than you ever could by simply leaving it in an
automatic mode. But also understand
that the higher power settings you're using will also produce more interference
or clutter on the screen than you are used to seeing at low power settings.
The
button or knob on your machine marked Clutter Control or Discrimination should
be glued in the off position. These
features are meant to remove clutter and by doing this, they can also filter out
useful information, too.
Why
bother setting up the machine to give you the greatest amount of information if
you are only going to use filters to take some of it away again.
Filters do just what the name implies, they filter out weak signals,
which can often provide information that you want and need.
Learn to read the important signals through the mild interference that is
created by peaking the transducer and stay away from the filter controls.
A
good example of a time for keeping the power up and the filters off is when you
go night chunking for tuna. There's
a lot more to chunking than just setting up on an edge or drop-off and tossing
butterfish in the water. It helps
to know if there is a thermocline in the area and at what depth.
It
is also helpful to know if there is baitfish in the area, because you have a
much greater chance of getting a bite started if the tuna are on bait in the
area. By peaking the transducer and
keeping the filters off, you will be able to interpret the return signals to
show the thermocline and small pods of bait.
Dealing with a little clutter or interference on the screen is worth the
additional information you get from keeping the gain up.
Interference
comes in two forms, returned signals from another machine or random electrical
impulses that show up on the screen during normal operation.
Interference from another sounder operating on the same frequency will
show up on your screen as a series of dots or dashes that run in symmetrical
lines, usually diagonally across the screen.
The rhythm they exhibit is a constant and the marks on the screen will
be, also. Do not bother trying to
remove them with filters or by turning down the gain.
If you know what it is that you're seeing, you can disregard that
information and simply read through it.
Other
forms of interference will be shown as small marks on the screen, usually just a
blanket of lit up pixels in no particular form. It can resemble what we call snow on the TV screen at home.
Squid, anchovies or other small baitfish will show on the screen as
larger spots of color because of their size.
When they are concentrated, they can show up as a large area of color or
a blob on the screen.
Even
an algae bloom will show up stronger than interference, if you know what your
are looking at is algae. Again, my
suggestion is to learn to read through interference and you will still be able
to pick out schools of bait at mid-depths or on the bottom, once you get a
little practice under your belt.
One
depthfinder function that will help you better define difference return signals
is screen speed, the speed at which images move across the screen.
Slowing down the speed is like watching the Super Bowl on a Sony Watchman
with a two-inch screen, as compared to watching it on a 27-inch television.
The picture at higher screen speeds is cleaner, crisper, provide more
detail, increased definition and higher resolution and is not distorted or
squished as when the screen speed is slow.
Leave the screen speed turned to its highest setting to expand the
information that is passing across it. At
faster speeds, you can also discern interference signals more easily.
Interpreting the Screen
Thermoclines
are air conditioning for fish. Large
tuna do not like the same warm surface water as blue marlin, but they do like
the clean water and forage fish the warm water often holds.
Large tuna will often hold close to the thermocline layer where they find
cooler water that is more suited to their temperature preference.
Hence, more tuna are caught chunking at night than during the day
trolling during warm water conditions.
Radiant
sun warming has subsided at night, surface temperatures cool a little and, quite
often, the tuna will turn on. Sure,
we can get a blast of surface feeding fish when a school goes on the feed during
the day, but those blasts are usually early morning affairs and very short in
duration. But, if you find a
significant thermocline, you can increase trolling success by putting baits or
lures on the thermocline with downriggers, but you have to be able to determine
the depth of the thermocline, first.
Anglers
chasing swordfish make it a point to place their baits just above or below the
thermocline to get their best chance at catching one of these night feeding
billfish. When they are cruising
looking for bait or actively feeding the love the area around the thermocline
because it provides cool, clean, highly oxygenated water usually full of life.
Thermoclines
normally appear as a constant faint blue line that holds even in relationship to
the bottom contour. They can be
found as close as 50 feet from the surface when there is a strong upwelling
present, but normally will be found somewhere in the top third of the water
strata. Some fishermen misread them
as interference, but they do not resemble true interference when you know what
you're looking at.
Just
as using downriggers during the daytime increases your chances of trolling a
fish on the thermocline, you can use them to get chunk or whole dead baits deep
on the thermocline at night. You
can also use jigging techniques for tuna near the thermocline both during the
day and at night, but the key is knowing where the thermocline is positioned
below the boat. We often catch tuna
on 24-ounce jigs tipped with a whole squid when the fish are holding on the
thermocline.
It's
important to know that thermoclines are not always found at the same depth
throughout an area. They can vary
when upwellings in one area are stronger than in others.
When trolling and marking thermoclines, it's a good practice to mark the
loran TDs or Lat/Long of significant thermoclines so you can return to them for
night chunking or for another pass later in the day.
Upwellings
occur when strong tidal influences converge at a drop-off, along the edge of the
shelf or near a seamount. When the
tidal flow crashes into an area of dramatic bottom depth change, it forces
nutrient rich, cold water nearer the surface.
These upwellings very often never make it all the way to the surface, so
they can only be detected through the use of a depthfinder set up properly to
read them. When upwellings make it
all the way to the surface, they are easy to see as rips and tidal edges.
Most
offshore fishermen have seen tuna stacked up on the edge of a sea mount or
drop-off, holding patiently in position like ranked soldiers, and no matter how
many times you trolled over them, you did not get them to come up and hit a
lure. These fish are sitting on
that faint blue line you now know how to detect.
When you find fish like this, you've found the perfect place to start
chunking, put out a bait on the downrigger or to stop at and drop a jig.
Color
machines can tell you the type and amount of baitfish and gamefish you have
under the boat, but it requires you to use the SWAG (Scientific Wild-Ass Guess)
method in the beginning. When you
are catching gamefish and there are schools of bait concentrated in the area and
being marked on your depthfinder, when you put the first fish on the deck, check
to see what it is spitting up. If
it doesn't oblige, check the stomach contents when you collar the fish.
Is
it squid or anchovies? Let's say
the fish was helpful and spit up squid. You
know what the fish were eating when you passed over the school of bait and
hooked up, so you now know what a school of squid looks like on your color
sounder screen. That provides a
reference for future fishing and you can determine whether you're marking squid
or other bait, the next time out.
A
couple of references that I have found from my experience have shown that squid
school evenly and their image is returned to the screen in a relatively even
coloration solid right to the edge of the school. Anchovies and other small baitfish are represented with
thinner edges around the school because they try to ball up tightly toward the
center to stay away from predators that feed around the edges.
The school usually shows up with light blue edges, fading into green or
yellow and then even red, depending upon the size and mass of the school.
Knowing
and understanding the way your machine represents different types of bait and
gamefish on the screen comes from observing what you are catching and what the
fish caught were feeding on. You
must catalog these readings in your mind's eye for future reference, so the next
time you come across similar readings, you know what they are long before you
put the first fish in the boat. Combine
all the information you get from your depthfinder and you will have a winning
combination that will put more fish in your boat and make your fishing efforts
more interesting, too.
Remember the four basic procedures for getting the most from your depthfinder offshore: 1) Always peak your transducer; 2) Leave clutter and discrimination mode controls turned off; 3) Learn to read through minor interference; 4) Always work with the screen speed turned to its highest setting. By following these simply procedures, you'll be seeing a much wider range of information on your depthfinder's screen, and putting more fish on ice.