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How to Buy Fish Finders and Depth Sounders

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Being able to tell how deep the water is beneath your boat has come a long way from a lead weight on a line. Today’s technology will tell you accurate depth and indicate the type of bottom structure. Emerging technology can even show what is around your vessel in graphic detail, displaying fish suspended among pilings.  Here’s a brief primer on How to Buy Fish Finders and Depth Sounders

Traditional downward-looking sounders and fish finders have three primary components: the display, the sounder module and the transducer. The sounder module sends a signal to the transducer that broadcasts a sound wave into the water column. As that sound wave bounces off dense matter such as fish and structure, it is reflected back to the transducer. This information is sent to the module to be interpreted and displayed in a graphic format on the display screen.

The choice of display is an important decision. Bigger is usually better (albeit more expensive). Screen resolution is important. If a smaller screen has a higher resolution, it might outperform its bigger brethren. If you plan on splitting your screen to show zoom screens or other sounder information, or if you plan on sharing the screen with a chart-plotter, you should go with as large a screen as your console real estate and budget will allow. If you go with a system with side-by-side multi-function displays and a separate sounder module, you can run a chart-plotter on one screen and have a full screen fish finder on the other. This can be the best of all worlds, but the cost for these systems is considerably more than for a self-contained, single-display system. Manufacturers such as Raymarine are now offering the ability for your smart-phone or tablet to act as a repeater for your sounder. The company has developed an app that allows full control of some of its displays from phones or tablets.

The sounder module, or core processor of the sounder, is another consideration in how well your sounder or fish finder will work. You can spend a lot of money for high output power, which is not needed if you are fishing inshore or near-shore. Think of the transmit power as the brightness of a flashlight. Low power fish finders are like penlights that work fine in your cockpit. Mid-grade sounders are like Maglites that help you see to the end of dock. The highest power units equate to a 4 million-candle spotlight that can illuminate a distant channel marker.

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Inexpensive fish finders for small boats in waters 200 feet or less can have an output power of between 100 and 300 watts. The 500- to 600-watt units boast decent resolution to between 400 and 1,000 feet. (Note that many manufacturers rate the range of their sounders in freshwater, which tends to give deeper capability than denser saltwater.) The 1kW, 2kW and 3kW processors are designed for blasting a signal in the deepest trenches. The 2kW and 3kW processors are commonly seen aboard commercial, ocean-going fishing vessels but the 1kW units are becoming standard on many offshore recreational fishing vessels. They provide excellent resolution past 1,000 feet for finding canyons and thermals where trophy fish congregate.

The operating frequency and transducer type also play important roles in resolution at any given depth.

Most lower priced systems, such as Garmin’s Echo line or Lowrance’s X-4 series, will run on 200 kHz frequency, with some offering dual frequencies of 50 kHz (or 83 kHz) and 200 kHz. Lower frequencies travel better over deeper depths, so high-power deep-water units typically operate at 50 kHz or lower. Frequencies of 200 kHz or higher provide better resolution in shallower water.

Transducer types are transom mount, in-hull (affixed to the inside of the hull to shoot their signal through the hull), or thru-hull transducers (drilled and mounted through the hull with the transducer penetrating the hull). All require clean, uninterrupted water to pass under them.

Transducers mounted to the lower portion of the transom are usually the best option for smaller boats. Stepped hulls, I/O or inboard boats and surface drives are better suited to use an in-hull or thru-hull transducer. Some transom mount transducers can become in-hulls by epoxying them inside the hull (never use silicone or 5200 type materials, as they absorb the signal the transducer is emitting).

Most in-hull models will either be a puck style or have a housing that is affixed to the hull and filled with mineral oil. The transducer is attached to the housing with the element suspended in the mineral oil. These have the advantage of not having anything on the outside of the vessel that can be struck, thus eliminating the risk of leaks or damage to the transducer. Because they are transmitting through the hull itself, there is a slight loss of sensitivity and range. Locate the in-hull unit as far back as possible so that clean water passes under it even at higher speeds. In most cases the hull location should not be more than an inch thick. Foam or hollow core boats are not good options for these transducers unless a solid mounting point is created. In-hull transducers also cannot be used on aluminum and alloy hulls.

Thru-hull transducers are the primary choice for larger vessels and others where transom and in-hull units don’t work. Most thru-hull transducers are bronze, stainless or nylon. The material they are made of is particularly important if you are mounting them to a metal-hulled vessel.  Because you have to drill a hole in the hull to mount these transducers, it is advisable to have it done professionally to ensure it is correctly mounted.

Some transducers by Airmar (the producer of many of the transducers used by manufacturers today) are flush mountable with pre-angled elements – an advantage over traditional transducers that require fairing blocks and are not flush with the hull, increasing drag and chance of impact. Transducer sizes are proportional to the power and frequency they operate on – the more power the larger the transducer.

If you have more than one sounder, fish finder or a combination of either, they should never be on simultaneously if they are operating on the same frequency, as they will interfere with each other. We are seeing a wider range of frequencies offered than ever due in part to a new era in fish finding. Chirp (Compressed High Intensity Radar Pulse) fish finders are high-power deep-ranging (and expensive) devices that use multiple frequencies to give incredible detail in deeper depths.

New products have changed the expectations of recreational anglers. Side imaging offerings from Humminbird and Navico have changed the look of fish finding with their high def, easily read images of structure on either side of the boat.

Sean Edmunds of Navico explained that its side scan transom mount transducer is about 11 inches long and 1.5 inches wide. Two elements look right 80 degrees, two look down 30 degrees and two look left 80 degrees. Because the side scanning elements are on such a high frequency and emit such a narrow beam, they can reach out as far as 350 feet on either side. The detailed information they return is astonishing.

Bill Carson of Humminbird demonstrated that his company has added its own twist to its existing side-viewing technology with a deployable (not while under way) transducer. It is shaft-mounted in what looks similar to Humminbird’s Talon anchoring system. Once deployed, this transducer is capable of doing a 360 sweep, similar to radar. This not only enables excellent side views, but also can see all around the boat and focus in on pie-shaped areas of interest. In his words “this eliminates dead water fast,” thus enabling fishermen to maximize their time on the water.

A combination of new technology and old school tried and tested sounders has produced a greater choice for anglers and mariners than ever before.


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Glenn Hayes
Glenn Hayeshttp://www.HayesStudios.com
Glenn Hayes is a writer and photographer based out of west central Florida and has marine industry background spanning almost a quarter century. He can be reached through his web site www.HayesStudios.

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