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Sonar, which stands for “SOund NAvigation and Ranging,” is a technology used to detect targets underwater. It is similar to radar, but instead of detecting targets in the air, sonar detects them in the water. Sonar can be categorized into two types: passive and active.

Passive sonar involves listening for sounds transmitted by the target itself. In submarine films, you may have seen operators wearing headphones and listening for sounds of approaching vessels. This is an example of passive sonar. It relies on the target generating sound for detection.

Active sonar, on the other hand, uses transmitted sound signals to detect objects and underwater terrain. It measures the time it takes for the echoes to reflect back from the target to determine the distance. The sound signals are sent out from the sonar system and the echoes are received and analysed. The time it takes for the echoes to return provides data on the distance to the target. Advanced sonar systems can also provide additional details such as the hardness of underwater terrain and the size and number of fish.

In modern leisure boats, active sonar technology is commonly used. The sound waves emitted by the sonar system occur thousands of times per second and are usually in the ultrasonic range, which is not detectable by the human ear or fish.

Sonar can be utilized on boats for various purposes. The following are some marine electronics that incorporate sonar technology:

1  Depth Sounders or Echo Sounders: These instruments display the vertical distance between the boat and the seabed as a numeric value. They provide essential depth data for navigation and can be used to set alarms for shallow water conditions.

2  Fishfinders: Fishfinders combine depth sounder functionality with detailed imaging of underwater terrain and fish. They provide a color-coded picture of what is underneath and to the sides of the boat, including suspended objects, swimming fish, and temperature gradients in the water. Fishfinders are useful for anglers and anyone interested in exploring and understanding underwater environments.

3  ForwardScan or Forward-Looking Sonar: This specialized type of sonar sends sound signals ahead of the boat to provide a detailed picture of the underwater terrain that the boat is approaching. It offers safety benefits, especially when navigating in uncharted or poorly surveyed areas.

To utilize sonar on your boat, you will need a transducer. The transducer is a crucial component that acts as a powerful loudspeaker and microphone underwater. It emits sonar signals and listens for the echoes that bounce back from the seabed and other targets.

The choice of transducer depends on your specific requirements and the depth instrument, fishfinder, or multifunction display (MFD) you intend to use. Transducers need to be installed correctly, ensuring direct water contact or acoustic connection to the water, proper alignment, and a clean surface free from coatings or fouling. There are different transducer types available, including transom mounted transducers and those requiring dedicated holes in the boat.

In addition to the transducer, you will need a compatible display or system to connect and view the sonar data. Integrated systems can share depth data across a network, allowing you to view the information on multiple displays. Planning your sonar system based on the level of detail and performance you desire is important.

It’s recommended to consult with experts or professionals who can provide guidance on the best sonar options for your specific boat size, type, and purpose. They can assist with choosing the appropriate equipment and ensuring proper installation for optimal performance.

For installations contact Harald Farthofer Ph: 0403 950 709



Published in print October-December 2023