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Note: All prices in US Dollars
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Whether you call it a fishfinder, sounder, color scope, or sonar, it is no surprise that fishfinders are the number one
selling piece of electronics for boats. After all, most of us go out there to “fish”, some of us better than others. Of course,
the fishfinder can also help to keep the prop out of the mud and off the stumps while you’re looking for that new fishing
hole. The wide variety of applications for fishfinders and the vast number of boat styles has created a market with a huge
number of different units available.
Understanding fishfinders is pretty straight forward. The principles go back to the turn of the last century when science discovered that sound waves move through water at a constant speed. By sending a sound wave through a sensor in the water (known as a transducer) and measuring the time it takes to bounce back, you can determine the distance to the bottom or to the object in the water. Increasing the transmitter power and lowering the frequency will allow the sound wave to travel further. Transducers…there are three basic styles of transducer. The key difference between them is the way they attach to the boat. Transom mount transducers are bolted onto the outside of the transom and down below the bottom line of the boat. This style is ideal for small boats with outboard motors and any trailer boat. Thru-hull transducers are literally bolted through the hull of the vessel. They are used on larger boats and especially on boats with in-board engines. Thru-hull transducers are installed forward of the prop to prevent cavitation interference with the sounder’s readings. This style transducer often requires a “fairing block” to square the transducer face to the bottom and provide smooth passage through the water. The third option is an In-hull installation. This is a transducer glued inside the bottom of the boat where it actually “shoots” sound waves through the hull into the water. This only works on solid fiberglass hulls that do not have other core material (like wood or foam). In the old days, customers would take a transom mount transducer and just epoxy it on a flat spot inside the hull. Today, there are units specifically designed to offset the dead-rise in the hull and high performance units that actually sit in a bath of mineral oil. Frequency… as we discussed earlier, the lower the frequency the further the sound wave will travel through the water. The traditional standard was 200 kHz transducers for “shallow” water, less than 200 feet, and 50 kHz for deeper water. More sophisticated machines offered dual-frequency capability with the option to transmit in either 50 or 200 kHz from the same transducer. Today, dual frequency machines are common and some manufacturers have even branched out into tri-frequency machines. Digital Sounder Technology… is the new frontier in fishfinders. Basically, the digital sounder varies the speed, timing, and power of the pulse. Different aspects of the target are highlighted under each of the pulse conditions. This allows the sounder to compile the various “pictures” into a single enhanced image. By adjusting the timing of the sound waves and knowing when to expect the return, the processor can maximize the time it takes to paint the image, making for a faster response time. |
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