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Sonar Noise Clutter

Old 12-27-2016, 02:34 PM
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Good Morning: My boat is a Hydra Sport Lightning 212 CC. Bought the boat used a couple of years ago and installed a Raymarine Dragonfly GPS/fishfinder (Model E70085). Sonar screen is full of white dots (noise). Adjusting unit's noise filter and sensitivity does not help. Replaced plastic transom-mounted transducer with model CPT-80 Raymarine bronze thru-hull (per manuf. instructions). No improvement. MFD is mounted at helm with small compass about 12" to left of unit. VHF is about 12" to right of unit. Problem does not go away if VHF is turned off. Removed stereo when I bought the boat. Only other electronic stuff @ the helm are the typ. Yamaha instrumentation for the engine performance (fuel level, engine tilt, battery voltage, etc). Raymarine tech suggested trying a ferrite suppression clamp. Researching such clamps yielded suggestions for putting them all over the place (power wiring, antennae cable, MFD cable, etc. Also read a little about 'Power Line Noise Filter'. Any suggestions on what best to use and where to install the device(s) would sure be helpful. Thanks - Al
Old 12-27-2016, 02:50 PM
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Before looking at potential solutions, it would be best to understand the problem in better detail.

Do you see the same level of interference when stationary? Does it only occur with engines running?

Perhaps you've already elaborated on some of these points with Raymarine and that's why they've made their suggestion. If so, ask them to be more specific on where they recommend you place it.
Old 12-27-2016, 02:54 PM
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Most probably it's electrical noise from the engine. It can be coupled directly through the power wires or it can couple into the transducer cable.

If you stop the engine and the noise disappears, you know it's the engine. To check if it's coming directly from the power wires try to power the sounder directly from another battery.
Old 12-27-2016, 04:47 PM
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Problem goes away at low speed (about 4-5 knots). At normal trolling speed (8-12 knots) problem is intense. Engine is a 2004 Yamaha carbed 150 2 stroke and is about 8' from helm. If it is due to the engine electronics, any suggestion on a cure would be helpful.
Old 12-27-2016, 08:00 PM
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Are you certain the noise is electrical in origin, or could it be flow noise, bubbles in the water etc.
Old 12-27-2016, 08:33 PM
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Here's a couple of test procedures.
Do a dead ship test...
1 Bring vessel upto speed of worst interference, then turn off ignition.
If noise disappears instantly, it is electrical. If it slowly disappears as boat slows down it is transducer.
related.

2 From a standing start, turn off sounder and disconnect transducer, turn on sounder and repeat procedure if noise reappears and goes away with ignition off, it is power supply related not transducer.

3 Turn off transmit pulses if possible on sounder or go deep. If noise changes, it is transmitter and receiver related. If noise stays the same it is detecting passive noise not related to the transmitter.

Try adjusting gain down as noise in clear water column is similar to what you describe, and is also a high gain issue.

Finally make sure your tacho gauge wiring, if sensing engine RPM from alternator or magneto is clear of transducer cable as this is the only 'frequency' related item running the length of the boat parallel with the ducer cable.

As other have said, we need to know what it is, before we can advise on how to fix it.
Old 12-27-2016, 09:10 PM
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Try some of the tests listed above, but it sounds to me like the transducer isnt installed correctly or its in a bad location.

Take a pic of your transducer from the side and from the back so we can see how its installed in relation tot he hull.

Also look at the bottom of the hull in front of the transducer. The hull needs to be dead smooth - no strakes, thru-hull fittings, steps, channels. etc in front of the transducer. Any thing like that will cause turbulence and bubbles as the boat speeds up which will cause increasing "noise" on the screen.
Old 12-29-2016, 02:02 PM
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Thanks for the good ideas. I also suspected the transducer as the screen would be clear at real low speeds. The transom mount was done exactly per manuf. instructions, then the height was adjusted in an attempt to get rid of problem. Finally removed transom mount and installed bronze thru-hull on starboard side with faring block in strict accordance with manuf. instructions. Hull is smooth and clean. Transducer is firmly attached an in line with the hull. Cable routing for the thru-hull is a little better than the transom mount (not as close to the battery compartment). Even if I goofed badly with the thru-hull, there should have been some variance in the sonar picture. The suggestion of getting up to speed then shutting off the engine sounds real good. Bad conditions at the launch right how and I thought I'd try the ferrite clamps suggested by Raymarine. Has anyone had experience with these and any suggestions on placement. Raymarine just said to place one on the transducer cable. A little study suggests that one placed on the VHF antennae and the (+) wiring to the helm might help. - Al

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