Strakes, steps, intakes and outlets, rivets, thruster tunnels, props/shafts will all do this.
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Transducer installed behind a hull feature that's causing bubbles.Low-profile through-hull transducer installed in a boat that is too big or too fast for that transducer type. Low-profile transducers are only suitable for smaller and/or slow vessels which don't produce much of an aerated, turbulent boundary layer next to the hull. This is the second-most common sounder performance problem we hear about, and the one that most people know about: air bubbles across the face of the transducer. Example: an in-hull transducer installed in a double-skin fibreglass hull with a coring material: Gluing a transducer inside the hull is just asking for early failure (changed impedance, excess current, lack of cooling) and poor performance (glues and sealants do not effectively transfer sound energy from the transducer to the hull and then out into the water, and also spoil the designed beam-pattern of the transducer.) Never glue a transducer in-hull. In-hull transducers must only ever be installed a tank filled with fluid. cored fibreglass, aluminium, or above a rib, stringer or similar)
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Common causes are water ingress into the transducer (incorrect installation, through-hull transducers not bedded in sealant according to installation instructions), damage from submerged objects, grounding, crane lifting straps etc., or being operated out of the water (*never* run a sounder dry.) If a transducer needs to be tested, good dealers will have an Airmar TDT1000 transducer test tool. If a transducer acoustic element has a problem then it can fail to resonate correctly and output low power.
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From your newly-configured fishfinder page, Menu > Settings > Page settings > Edit data overlays.The idea is to compare the results from the two channels (frequencies.) If you have an RV system, Sonar and Downvision would be good. First, please set up a sounder page with at least two sounder channels displayed (for example, if you have a CP470, a two-way split with both Low Chirp and High Chirp at the same time would be great.It doesn't take a lot of either sound or electrical noise to start to cause problems. If you imagine the amount of energy contained in a sound echo coming back from a single fish 100m down, or the bottom 500m or more down, and then picture that echo moving the transducer element and that movement then inducing a voltage onto the signal cable, I think that gives a bit of an idea of the low level of the electrical signals on the transducer cables, which can be less than 0.00001V. Every electronic system contains noise (unwanted randomly fluctuating voltages in parts of the circuit) to some degree, and both the sea and boats are relatively noisy places so there will always be a background noise level: the sounder needs to be able to clearly hear the echoes from fish and the bottom above this noise. What a sounder needs in order to perform well - some backgroundĪll sounders, of whatever brand, require as large as possible a difference in the signal level (voltage on the transducer cable) and the background noise level.