The principle of the sounder for fishing from a boat: from theory to practice

The sonar has become an indispensable tool for anglers, turning fish hunting from a game to a science of chance. But how can this device, the size of a palm, see the underwater world through the water? physical basis of sounderSignal processing features and practical nuances of use on the boat - from sensitivity settings to the interpretation of the screen with "arches" and "points".

You'll find out why. Lowrance, Garmin or Deeper They show a different picture in the same place, how the frequency of ultrasound affects the detail of the scan, and why the sonar sometimes lies about depth. Why in shallow water with a frequency of 200 kHz you will see every blade of grass, and at a depth of 30 meters it will become uselessReady to dive?

Echo sounder physics: how ultrasound "paints" the bottom

The basis of any sounder is the principle sonar Sound Navigation And Ranging: It emits ultrasonic pulses that bounce off objects underwater and then come back, and the delay between sending and receiving a signal allows you to calculate the distance to a target.

Depth (m) = (Speed in water × Latency time) / 2

The speed of sound in fresh water is ~1480 m/s (at +20°C), in salt - ~1530 m/sThat is why sea fishing sonars often require manual calibration of the speed of sound - otherwise the error at a depth of 50 meters can reach the maximum of the maximum. 1–1.5 meters.

• 🌡️ Water temperature: at +5°C, sound propagates 30 m/s slower than at +25°C. Modern sonars (e.g., Garmin Striker Plus) automatically compensate for this.
• 🧂 Salinity: in the Baltic Sea, the speed of sound is 2% faster than in the lake, which is critical for accurate measurements.
• 🌀 Turbulence: On fast-flowing rivers, the signal can be “lubricated” creating false echoes.

⚠️ Attention.: If your sonar suddenly starts to show a depth of 10-15% greater than the real one, check the sound speed settings. 90% of the time, the problem is that the water salinity is incorrectly indicated.

Frequencies of the sonar: the higher, the more detailed (but not deeper)

The frequency of the ultrasonic emitter determines how much the sonar "sees" the underwater world, and here is a simple rule:

Frequency (kHz)	Max. depth (m)	Details	Typical application
50–83	1,000	Low.	Deep sea fishing, search for relief
77–120	300	Medium	Universal (lakes, rivers)
192–200	100	High.	Shallow water, search for small fish
455–800	30	Very high.	Sports fishing, search for bottom fish

For example, a sonar Deeper Pro+ 2 frequency-operate 290 kHz (a wide beam for searching for fish) and 90 kHz Switching between them allows you to determine more precisely whether the pack is standing above the pit or at the edge of the pit.

Key nuanceHigh frequencies give a narrow beam (e.g., 15° bal Lowrance HDS Live 200 kHz), which increases detail but reduces the area covered. Low frequencies, on the contrary, disperse more widely (see below).60° 50 kHz, but they penetrate deeper.

Transducter: the eyes of the sonar and their location on the boat

Transducer (or converter) It's a sensor that emits and receives ultrasonic waves, and its type and installation determines 80% of the scanning quality.

• 🛥️ Trants: mounted on the transom of the boat, optimal for motor boats (e.g., PVC with transom wheelsMinus can create turbulence at high speeds.
• 🧲 Magnetic: attached to the boat hull from the inside (e.g. Deeper STARTComfortable for inflatable boats, but loses efficiency on aluminum shells.
• 🎣 Dropped.: suitable for shore fishing or for fishing from a stationary boat (e.g., Deeper CHIRP+You can throw it 50 to 100 meters.
• 🔧 Injurious.: is installed in the hull of the boat (relevant for boats), requires sealing, but gives minimal interference.

Critical error: installation of the transducer at an angle more 5° This leads to blind spots and distortions of depth, for example, if the sensor looks up, the sonar will show a false bottom 10-20% closer to the real one.

⚠️ Attention.On boats with an outboard motor, the transducer should be located left-handOtherwise, the turbulence from the blades will create a white noise on the screen, the optimal distance is 30-50 cm from the screw.

How the sonar processes the signal: from echoes to "arches" on the screen

The raw data from the transducer is a chaotic set of echoes that the sonar processor is doing to turn into a clear image.

1. Noise filtering: remove interference from waves, engine, other sonars.
2. CHIRP technology (if supported): instead of a single pulse, a series is sent with a varying frequency, which increases the detail.
3. Digital processing: signals are converted into pixels on the screen, for example, a strong reflected signal (fish, driftwood) becomes a bright point, a weak one (silt, algae) becomes dim.
4. Color-coding: in modern sonars (e.g., Humminbird HELIX) fish is shown in red, bottom in brown, algae in green.

Why does the fish on the screen look like an arch?Because the sonar scans a vertical slice of water, and when a fish swims through the beam, it first fixes its top (head), then its body, and then its tail, and that forms the arc. The wider the arch, the larger the fish: a pike 50 cm long will give the arch 2-3 times wider than a sticker.

How to distinguish fish from garbage on the screen?

Fish usually move horizontally and leave behind a tail of dots. Garbage (branches, bubbles) randomly moves up and down or hangs in one place. Garmin Panoptix) the fish is illuminated with special icons.

Practical echo sounder settings for effective fishing

Even the most expensive sonar is useless if it's not tuned to catch conditions.

• 📶 Sensitivity (Sensitivity): in shallow water, reduce to 70–80%To avoid noise, at a depth of >20 m, raise it to a depth of 90–95%.
• 🎛️ Contrast (Contrast): Increase if the fish merges with the background. In muddy water, reduce.
• 🔄 The speed of the scroll (Scroll Speed): set up on the current AutoAnd in standing water, Max for detail.
• 🎯 Scanning area (Depth Range)Always set 10-20% deeper than the real bottom, otherwise the large fish at its edge will remain invisible.

Example of settings for catching a pike at a 15-meter depth:

Frequency: 200 kHz (detail)
Sensitivity: 85%
Contrast: 60%
Scanning area: 18 m
Noise filter: Medium

Common Mistakes and How to Avoid Them

Even experienced anglers sometimes make mistakes that negate the benefits of sounder.

1. Ignoring the speed of the boatAt speeds >5 km/h, most sonars (except for Garmin Panoptix) lose up to 30% of accuracy. Optimal scanning speed 2-3 km/h.
2. Failure to account for boat materialAluminum and fiberglass enclosures create multiple reflections of the signal. narrow-beam (10–15°).
3. False thermoclinal positivesA sharp temperature drop (for example, at a depth of 8-10 m in the summer) reflects the signal as a “false bottom”.

Case in point: angler The PVC boat "Winger-420" complained that the sonar PiranhaMax The reason the transducer was placed too close to the propeller, and air bubbles were created on the move, blocking the signal, and after moving the sensor 40 cm to the left, the problem disappeared.

Fish Scanner vs. Fish Scanner: What's the Difference?

Many people confuse classical sounders with fish-scanner (for example, Deeper CHIRP or Garmin LivescopeThe main differences are:

Parameter	echoer	Fish-scanner
Type of scan	Vertical beam (2D)	3D or panoramic scanning
Screen update	1-2 times per second	Up to 10 times per second (real time)
Price.	From 5,000	From 30,000
Application	Search for depth, relief, flock of fish	Real-time fishing (e.g. jig)

Type scanners Garmin Livescope They show the fish in real time, which is critical for spinners, for example, you'll see a pike swim up to the bait and attack it, but these devices require perfect installation and consume a lot of energy. 1 A/h).

FAQ: Answers to frequent questions

Can the sonar work through the boat hull without diving the transducer?

Yes, but with reservations. Deeper START) may be scanned through fiberglass or thin aluminium (up to 4 mm); however:

• The signal loss is up to 40%, which reduces the depth of the scan.
• On boats with air cameras (for example, PVC inflatable floor) it won't work.
• It works best on smooth surfaces – irregularities create interference.

Why does the sonar show the fish where there is none?

There are several reasons:

1. False echoes from air bubbles (for example, after a shower or when agitated).
2. thermoclin A water layer with a sharp temperature difference that reflects the signal as a “fish”.
3. Garbage: branches, algae, plastic bags.
4. Sensitivity settings The sounder catches even weak reflections.

Solution: Reduce sensitivity, turn on the noise filter (See also:Noise Rejection), check the temperature profile.

Which sonar is better for catching PVC from a boat?

For inflatable boats, the best:

• 🔹 Deeper Pro+ 2 - tossable, works via Bluetooth, frequency 290/90 kHz.
• 🔹 Lowrance HOOK Reveal 5 - Transfer, with technology DownScan for a detailed scan.
• 🔹 Garmin Striker 4 - Budget version with CHIRP, is attached to the transom.

Avoid cut-in transducers – they are difficult to install on PVC without the risk of damage.

Can I use a sounder in winter from ice?

Yes, but with limitations:

• The transducer must be submerged in water (for example, through a hole).
• In the cold, LCD screens can "brake." Use models with a LED lighting (for example, Humminbird ICE Helix).
• The battery runs out 2-3 times faster. Take a spare or use it. LiFePO4- Batteries.

How does the sonar show the fish under the boat when the beam is downward?

Echo sounder scans coneIt's not vertical. It's like the angle of the beam. 20° and a depth of 10 m the diameter of the scanned area at the bottom will be ~7 metersFish swimming in this cone will be recorded.

• The closer the fish is to the edge of the cone, the weaker the signal.
• In shallow water (<5 m), the cone narrows and some fish may remain out of sight.