Understanding fish finders and the meaning of power

The second boat I owned came with an old Lowrance fish/depth finder. Now, four boats and five kayaks later, I am beginning to figure out these wonderful devices.

My recent epiphany came when my Lowrance X85 finder got a significant amount of water inside and shorted out. I had struggled with this finder for about a year. It's very powerful but the technology is old and replacement parts are expensive. After its failure I started looking around at various finders with the goal of spending about $125 for a finder, cover or case and a speed sensor. I settled on the Humminbird 560 (middle photo) and was able to accomplish my goal within budget by finding a fabulous deal Thanksgiving Day. I mounted the transducer inside the hull on my sled and took it out for a test drive. The unit worked great at slower speeds but lost the bottom at higher speeds. I did some test to see if the problem was the location of the transducer, the voltage interference and or the adhesive. No matter what I did, I had the same results. So I started doing more research. I soon realized that the X85 had an RMS (watt) rating of 375, while the 560 has a RMS rating of 250. I thought back to the X85 transducer I had put in the hull of the sled  and remembered the loud tapping sound, something that was missing from the 560 transducer. 

Currently, my two kayaks both have Hawkeye finders. The Hawkeye (see left photo) on my Redfish came with the kayak and is a magical unit. On several occasions I have marked fish on the finder and within minutes I got a bite. Although it only goes to 100 feet, it always works and marks fish even though the transducer shoots through the hull. The other finder is also a Hawkeye (right photo). It's older but it has a temperature gauge, fish alarm, is able to measure to 120 feet and distinguishes between large and small fish. However, it stops working intermittently, usually at the worst possible time. Needless to say this model is no longer manufactured.

So what does all this mean? Well as you are looking for a fish finder, pay close attention to the peak-to-peak wattage and the RMS. In a nutshell, the best advice I can give you is that the faster you plan on going in your kayak or boat, the higher the RMS you will need. In a later post I will discuss resolution and options.


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