Terminology 101

Terminology 101

Hybrid Dual Imaging

Similar Terms: HDI

Lowrance combines two award-winning technologies — Broadband Sounder and Downscan Imaging — to provide the best possible view of the water column in the one display.

Broadband Sounder - uses less power to see smaller Fishes and lure tracking at a deeper depth

Down Imaging

Similar Terms: DownImaging, DownScan, Down Scan, DSI, Down Scan Imaging, DownScans, Downscanning, DI, DownVision

Down Imaging, as the name suggests, is the ability on fish finders to provide detailed picture-like images of the bottom and structures directly below the Boat. The picture-like images are displayed using specific Down Imaging software that represents the returnSonar signal in a more realistic manner.

The term Down ImagingTM is a registered trademark (TM). OtherFishfinder brands have similar software, but cannot refer to it as Down Imaging, eg. Lowrance have trademarked their software/technology as DownScan ImagingTM (DSI).

The Frequency used for Down Imaging is typically 800 kHz (45°) and 455khz (75°) - hence the technology operates best in shallower waters. The 800khz Beam gives the sharpest image Resolution whereas the 455khz Beam gives the best overall image quality and depth.

When combined with Side Imaging technology, Down Imaging gives the user a full 180 degree view of the bottom. (c.f. Side Imaging, StructureScan)

Cone Angle

Similar Terms: Beam Angle,Beam Width

Cone Angle, Beam Angle or Beam Width refer to the angle of the Sonar Beam as it is leaves the Transducer and is transmitted into the water. The cone angle determines the underwater area covered by your Transducer. A wider/larger cone angle, will provide greater area coverage.

Transducer beam angles or cone angles vary between Fish finders and manufacturers. For example, a 200 kHz transducer may have either a wide (20°) or narrow (12°) cone angle. A 50 kHz transducer may have a 35° cone angle, whereas dual-Frequency or dual search Transducers come with both narrow (eg 12°, 200 kHz) and wide (eg 35°, 50 kHz) cone angles.

Generally, a wide cone angle is best for fishing shallow to medium water depths and narrow cones penetrate to deeper waters, but show less Fish and structure due to their narrow beam.

Usable Depth

Similar Terms: Maximum Depth,Useable Depth

Many marine electronic manufacturers will talk about maximum depths a Sounder should reach.

To our Way of thinking that is a bit like a cars speedo showing a maximum speed of say 250kph. That does not mean you will get that speed (unless you are travelling down hill with a very strong wind behind you!.)

There are many variables that affect the depth that a sounder can see the seabed.

These include:

  • Amount of salinity in the water
  • Thermoclines
  • Beam Angle
  • Transducer Frequency
  • Output power
  • Hull shape & Bubbles
  • Type of Transducer - In HullThrough Hull or Transom mounted

So when you see the term 'Usable Depth' this is a more realistic idea of what you can expect in most conditions - however there will always be an exception to the rule.


Similar Terms: Transducers,T/ducer,ducer,T/D

An electronic sensing device mounted in a Boat's Bilge or at the bottom of the Transomto provide data for a Depth Sounder. The transducer converts the electrical energy from the Transmitter into sound energy, that becomes the Sonar Beam projected into the water.

Internally the transducer consists of one or more Piezoelectric disks that expand by very minute amounts to create the sound wave. This mechanism, operates in reverse to convert the returning Sonar wave into an electrical signal that is interpreted by the reciever 


Similar Terms:

Radio: an electronic device that receives and converts a radio signal from a modulated radio wave into usable information; audio, video or otherwise

Depth Sounder

Similar Terms: Sonar

Electronic device that uses Ultrasonic waves to determine and display water depth


Similar Terms:

Sound waves of high Frequency than cannot be heard by humans. Sound waves higher than 20,000 Hertz.


Similar Terms: Piezoelectricity

Piezoelectricity is the charge that piezoelectric materials (eg Crystals, certain ceramics etc) produce when mechanical pressure is applied to them. Conversely, when those same materials are subjected to an electrical field they produce mechanical strain/deform.

This can be used to produce or detect sound, electronic Frequency generation and in micro balances among other applications.


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The rear, often flat section, of the Hull connecting the two sides of a Boat.


Similar Terms:

A Boat or vessel moving over the top of the water rather than through the water. Many smaller recreational vessels plan at higher speed, while ships and yachts never plan


Similar Terms:

The right-hand side of the Boat when looking toward the Bow.


Similar Terms:

To the back. At, close to or toward the Stern (rear) of the Boat.


Similar Terms:

Forward or front secton of a vessel


Similar Terms:

Located at the front/Bow of a Boat.