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Fish Finder Frequently Asked Questions Volume 1

Here are the answers to your questions about fish finders.
Lots more information HERE

What is RMS, peak to peak and why is it so special?

RMS (Root Mean Square) and Peak to Peak are used to describe the output power on your transmitter. This is why fish travel around in schools :-) Now, more power is not always better, its a combination of power and receiver capability.

What's the difference between wide and narrow cones?

A transducer with a wide cone (50 khz) scans more water and tends to lump things together whether it be fish, stumps, rocks, etc. A narrow cone (200 khz) can detect small details and focuses on structures at a greater depth. The disadvantage here is that it scans a smaller amount of water.

How do I tell what's on the screen?

This all comes down to density. Anything denser than water will give you an echo. So although you don't see the fish it doesn't mean they are not there. This is what makes you a better fisherperson. Weeds, brush, trees, rocks are great places to find fish. You just have to develop your skill to recognize them and then you can land your big one.

What's better LCD or Flashers?

Although it is easier to read a LCD that gently scrolls across the screen, they are both basically the same. Think about those vertical columns of pixels we talked about before. Thats the same thing your getting in a flasher without the LCD taking a few soundings, doing some averaging and some filtering before you get to see it. Its all about "real" time, by the time you get to see it, it could be gone.

How Does A Flasher Work?

Fish Finder Glossary of Terms


Acquisition Time

is the time it takes for your GPS to acquire a fix on your position.

Actual Sonar Returns

are the targets you get displayed as arches on your screen when the Fish I.D. is turned off.

Advanced Fish Symbol I.D.™

is part of the Lowrance system which when turned on automatically interprets sonar echos and displays them as fish symbols. Also known as Fish I.D.

Advanced Signal Processing

is a component of the Lowrance system which automatically fine tunes your sonar settings for clarity and accuracy. ASP is a noise rejection system that evaluates and constantly adjusts for speed, water conditions and interference. It takes into account equipment like bilge pumps, engine ignition, wiring and air bubbles on the transducer. Reducing unwanted marks on the display.


are the sounds you hear so you don't have to keep looking at the screen. These can be turned on or off or set for certain events. Usually 3 different sonar alarms, Fish Alarm, Zone Alarm and Depth Alarm. Of course the fish alarm goes off if it reads and echo of a fish. The Zone Alarm is a bar on the side of the screen and any echo inside the bar triggers and alarm. The depth alarm goes off if your current position is outside the shallow or deep setting.


is your height above sea level.


gives you the benefit of illumination at night or in low light.

Bearing (BRG)

The exact compass direction from where you are to the next waypoint.


is caused by turbulence which creates air bubbles around your transducer. The signal from the transducer is then reflected back and creates noise which intereferes with your echoes making it impossible or difficult to see fish, bottom and structures.

Chart Speed

is the speed at which your picture scrolls across the screen.


is the actual time it is.

Cold Start

The first time your new GPS receiver powers up, searches and locks onto the satellites. This may take some time because it is looking for your approximate present position, local time and date.


is the Lowrance component that separates fish and structures on or near the bottom from the actual bottom.

Course Deviation Indicator

shows you your distance to the side of the actual course line.

Course Over Ground

is the current direction you are actually travelling.

Cross Track Error (XTE)

is the digital reading on your GPS steering screen indicating exactly how far you are off course from the center.

Differential GPS (DGPS)

is now and international maritime standard created by the U.S. Coast Guard to improve GPS accuracy to 10 meters. Requires and added beacon receiver to communicate with the standard GPS unit.

Distance (DIS)

is the distance remaining between your present position and a waypoint.

Distance To Go (DTG)

indicates in a digital readout the remaining distance from your present position and a waypoint.

Estimated Postion Error (EPE)

A calculation using geometry, satellite position, time clock offset, satellite signal quality and more to estimate the accuracy of your positon.

Estimated Time En-Route (ETE)

Using your speed and direction a calculation is made to estimate the time to the next waypoint or pre-selected waypoint.

Event Marker

Using and icon, a graphic symbol is placed on the plotter display to represent an interesting event to be reviewed at a later time.

FasTrack™ (Lowrance)

A standard feature which displays flasher-style sonar in a vertical column on the right of the screen.

Film SuperTwist

is the technology used by Lowrance on their Liquid Crystal Display. It provides excellent screen reading in direct sunlight, backlighting at night and from any angle.

Fish Arches

are the boomerang shapes displayed on your screen which indicate fish.

Fish Symbol I.D.™ (Lowrance)

See Advanced Fish Symbol I.D.

Fish I.D.™ (Humminbird)

When a target is detected and Fish ID is on a Fish ID+ symbol with depth is displayed. The size of the symbol shows the strength of the sonar return.

Fish Reveal™ (Lowrance)

uses 10 adjustable levels of gray tones to help you expose fish in surface debris, thermoclines and weed beds when using actual sonar returns.

Fish Track™ (Lowrance)

You have to have the Advanced Fish I.D.™ and Fish Track™ on for this to work. It gives the displays the digital depth above each fish symbol.


is a quality measurment of your receiver's position. 1 is poor, 9 is good.


a combination of scrolling sonar graph, digital LCD flasher and GRAYLINE® or COLORLINE™. It puts all the information on your screen in the two most popular formats.


is a floating transducer used when fishing from shore.

Global Positioning System (GPS)

is owned and operated by the U.S. Department of Defense and is a set of satellites orbitting the earth allowing people to pinpoint their location.

Grayline® (Lowrance)

is a patented feature used to distinguish between hard and soft bottoms.

Ground Speed (GS)

is the actual speed you are moving in a certain amount of time.


locates and displays fish at higher boat speeds with more soundings per second.


a graphic symbol placed on the plotter screen to mark an interesting event.


is the procedure that occurs when the new GPS receiver is turned on for the first time.

Magnetic North

is the location your compass points. It is located in Canada, several hundred miles to the south of the true north.

Map Datums

(Military Grid Reference System)

is an alphanumeric version of a numerical Universal Transverse Mercator grid coordinate.

Multiplexing Receiver



is visual clutter that appears on the display caused by unwanted signals being picked up by the fish finder.

Output Power

is the electrical energy applied to the transducer by the sonar transmitter.

Parallel-Channel Receiver

Your GPS tracks multiple satellites to give you the fastest, most reliable, accurate information under the worst weather conditions.

Peak to Peak

describes the output power of your sonar transmitter.


or "picture elements" are colored dots that form shapes on a liquid crystal display.

Plotter Display

Using your waypoints and markers your given a "bird's eye view" of your current position and the shortest route to a chosen waypoint.

Present Position

is where you are now in terms of latitude and longitude coordinates, displayed in degrees/minutes/thousandths of a minute.

Programmable Windows


Pulse Length

is the amount of time the sonar transmits a pulse into the water.




Root Mean Square


is the combination of two or more waypoints.

Satellite Status Display

Savable Plot Trails


Selective Availability (S/A)



The manual way to adjust your fish finder. The Advanced Signal Processing (ASP™) does this automatically.

Skimmer® transducers

feature a low profile for high speed performance. It's patented design helps prevent cavitation and other interference. Lowrance Sonar AngleTo better describe the Skimmer® transducer think about it as your headlight view from your
vehicle at night.
The light beams directly ahead but it also shines off to the side. Now, lets say there are signs one on each side of the road and as you drive closer to them they become increasingly visible. This is termed periphereal. This peripheral is the 20 degree coverage you get on the sonar section of the Lowrance LMS-332C. The sonar covers a 60 degree angle in total. At a depth of about 20' it covers and area about 25'. The deeper the water the more area it covers.

Basically there are two types of transducers a 50 khz and a 200khz.

50 kHz

200 kHz

  • Deeper depths
  • Wide Cone Angle
  • Less Definition And Target Separation
  • Susceptible To More Noise
  • Shallower Depths
  • Narrow Cone Angle
  • Better Definition And Target Separation
  • Less Susceptible To Noise


using sensors you can digitally display surface water temperature, boat speed and distance.

Speed Over Ground (SOG)


Steering Screen


Straight Line Navigation



All solid objects rising from the bottom that aren't part of the actual bottom.


are areas where layers of warm water meet cool water.

Time To To (TTG)

is a digital reading showing the time left from where you are now to the next waypoint.

Track (TRK)

is the direction you are travelling.


is your "antenna" that sends out sound waves and receives echoes that get displayed on the screen. An improperly installed transducer will give you nothing but problems.

So to avoid these remember the transducer surface (face) must remain in contact with the water at all times. It will not transmit or receive thru air. If the transducer clears water when planing or sharp turns your readings will stop until it is back in the water.

Air bubbles across the surface will also distort readings, therefore it is best to avoid placement near hull ribs and thru-hull fittings. The best position is located where the hull and transom meet and as near to the center of the transom as allowed.

True North

is at the top of the world and is not to be confused with magnetic north.


Coordinated Universal Time. Time at the Prime Meridian at Greenwich, England.


Universal Transverse Mercator


Velocity Made Good


your system voltage.


is a spot, destination or location that can be stored in device memory which can be recalled at a later date.


Wide Area Augmentation System is a satellite navigation system designed by the U.S. Federal Aviation Administration to increase the accuracy of GPS satellite navigation. It was originally created for aviation applications and because of satellite configuration you may experience a loss of signal in North America.


allows you to enlarge the sonar or gps map display for a closer look at small details.

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