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Navigation & Communication
Echo Sounders
A navigational echo sounder measures water depth by timing a sound pulse from a hull transducer to the seabed and back. On a drilling unit or offshore vessel it gives depth under the keel during moves and approaches. The sub-Category covers SOLAS echo sounders, their transducers, junction boxes and repeaters. Survey multibeam systems are a separate class of equipment.
How the sounder measures depth
A piezoelectric transducer converts an electrical pulse into a sound pulse and listens for the echo. Depth is half the travel time multiplied by the speed of sound, about 1,500 m/s (4,900 ft/s) in seawater. Lower frequencies, around 50 kHz, reach deeper water with a wider beam. Higher frequencies, around 200 kHz, give finer detail in shallow water. Many navigational sounders run both through dual-frequency or separate transducers.
The displayed figure is depth below the transducer unless the operator enters a draft offset. Get the offset wrong and every reading is wrong by the same amount, so check it at commissioning.
Key specifications
| Parameter | Why it matters | Typical classes or units |
|---|---|---|
| Frequency | Depth reach against detail | 50 kHz, 200 kHz, or dual |
| Depth range | Coverage for your waters | Metres, feet or fathoms |
| Transducer | Must match the sounder | Frequency, impedance, power rating |
| Mounting | Dry dock or diver to replace | Flush, tank, or through-hull |
| Outputs | Feeds to ECDIS and recorder | IEC 61162 DPT and DBT sentences |
Standards and what a used sounder must meet
SOLAS chapter V regulation 19 requires an echo sounder on ships of 300 GT and up. The IMO performance standard is in annex 4 of resolution MSC.74(69), and ISO 9875 is its test standard. It asks for a measuring range from 2 m to 200 m under the transducer, depth alarms, and a stored record of depth history that can be recalled. IEC 60945 covers environmental testing. A self-propelled drilling unit follows SOLAS through chapter 11 of the 2009 MODU Code, while a non-self-propelled unit takes its fit from the flag state.
Failure modes and inspection
- The transducer face cracks, delaminates or fouls with growth.
- Cable glands and the transducer cable leak, which drops insulation resistance.
- Transceiver boards fail, and older sounders printed the record on paper rolls that are hard to find.
- A wrong sound velocity or draft setting gives a steady error.
A survey measures transducer impedance and insulation resistance, compares readings with a known depth or a lead line alongside, checks the alarm outputs, and recalls the stored depth record. A transducer removed from a hull needs a close look at the face and the gland before reuse.
Documentation
- Type-approval certificate for the sounder model.
- The transducer model and serial it was paired with, from the installation record.
- Installation drawing showing the mounting and draft offset.
- Last service report.
Integration with your unit
The transducer is the expensive part to change. It sits in the hull, so replacing it means a dry dock, a diver change or a tank installation designed for removal. For that reason the practical buy is usually a display and transceiver that match the transducer already fitted. Check the frequency, impedance and power rating against the sounder's approved transducer list. Depth goes to ECDIS and the voyage data recorder over IEC 61162, and the sounder takes time and position from GNSS for the record.
Refurbishment, used or surplus
Sounder electronics cost little next to dry-dock time. A used or surplus transceiver that matches the fitted transducer is the common choice. When the transducer itself fails, fit a new matched set during docking rather than a used transducer with no history. OEM repair of a transceiver board is worth it only while the OEM still supports the model.
Related equipment
Sounders take time and position from GNSS receivers. Hydroacoustic positioning for DP is a different system, covered under DP position reference systems. Ask Naventr for the Seller's transducer details before you shortlist a sounder.
FAQ
Frequently asked questions
Can a used echo sounder run with my existing transducer?
Yes, if the sounder is built for that transducer's frequency, impedance and power rating. Read the transducer model from its label or the installation record and check it against the sounder's approved transducer list before you buy.
What standard should a ship's echo sounder meet?
A SOLAS echo sounder meets annex 4 of IMO resolution MSC.74(69), tested to ISO 9875, with IEC 60945 for environmental tests. The standard asks for a 2 m to 200 m measuring range, depth alarms and a recallable depth record.
Do I need a dry dock to replace an echo sounder transducer?
Usually yes, because most transducers are mounted through the hull or in a tank in the bottom plating. Some installations allow a diver change or have a tank built for internal removal. Check the installation drawing before planning the work.
Why does my echo sounder read a different depth from the chart?
The most common cause is a missing or wrong draft offset, since the sounder measures from the transducer, not the waterline. A wrong sound velocity setting, tidal height or a fouled transducer face can also cause the difference.
Is a navigational echo sounder the same as a survey sounder?
No, a navigational echo sounder gives depth under the keel for safe navigation and is approved to ISO 9875. Survey single-beam and multibeam systems map the seabed to hydrographic accuracy standards and need sound velocity profiles and motion correction.
Looking for echo sounders?
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