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Part II: Depth sounder basics
  |  First Published: December 2014



Last month Starlo talked about the absolute basics of using a modern depth sounder or sonar. This time, he takes it a step further and moves into the realm of slightly more advanced sonar signal interpretation.

In the first instalment of this double-header, I briefly described what depth sounders or sonar units are, outlined the basics of how they work, and explained that most new chums and casual users are best off to simply turn their units on, hit auto and let them do their own thing (after first ensuring that the showroom ‘simulator’ mode has been deactivated, of course). For some people, this will be enough.

Naturally, however, many keener sonar users will soon wish to begin exploring the wider capabilities of their sounders by tweaking and twiddling the various controls. How these work varies somewhat from one brand and model to another, and I can’t stress strongly enough the importance of carefully reading the manual that came with your sounder, as well as jumping online to watch any video clips or tutorials pertaining to it. There’s a remarkable amount of information out there, and a simple search engine query listing the make and model of your sounder will most likely bring up all sorts of useful (and not so useful) links.

You can refine this search process further by adding words or phrases such as ‘sensitivity’, ‘frequency’, ‘surface clutter’, ‘colour line’, ‘scroll speed’ and so on to find out more about those various functions and tweaks, then apply them when on the water. In many ways, this is not unlike tuning a television in order to obtain the clearest and most pleasing picture for your eye. The best settings to use will vary slightly depending on the depth of water you’re operating in, as well as the speed of your boat and the amount of suspended matter in the water column. There’s no ‘one size fits all’ answer to the best combination of settings, so you may need to fiddle a bit from day to day or even hour to hour, but don’t become fixated with all this button pushing and forget that you’re out there to catch fish! Also, learn how to return your unit to its factory default settings in case you screw things up!

Finally, it’s worth noting that sounder technologies have improved at an exponential rate in recent years, and the quality of underwater imaging now available at a reasonable price is nothing short of staggering. Most makes now offer enhanced, high definition (HD) imaging technologies in their premium units under a range of titles such as CHIRP (compressed high intensity radar pulse), StructureScan, Side Imaging, DownScan, SpotlightScan and so on. Basically, these technologies all make use of more powerful and focussed beams of sound waves, combined with enhanced imaging software, to paint a clearer, more defined and detailed picture of what’s under, alongside and even ahead of your vessel. In many ways, these modern systems are like narrow-beamed spotlights compared to the virtual floodlights of older-style sonar. It’s really worth bearing that analogy in mind, because there are obviously times and places where the broader (albeit it less bright) illumination of a floodlight can actually be more useful than the narrow, confined but intense beam of a spotlight, and vice versa… It’s a matter of horses for courses and both formats still have their place.

In closing, I’ve included the standard sonar images I used with last month’s column, but now with their enhanced, narrow beam counterparts right alongside, as well as an interesting stand-alone StructureScan image… Hopefully you will find these screen shots, comparisons and the accompanying captions describing them ‘illuminating’, if you’ll pardon the pun

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