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Discussion Starter · #1 ·
I am curious.. my new LMS 520c system... when on the sonar, has A LOT of blue "noise" through out the entire water column" when on Auto Sensitivity. I can set the sensitivity way down to about 30% - 45% and it will all go away and leave me a nice clean white water column, with only a few specks of noise here and there.

My question is... is that noise normal??? Or is it being caused by an improper installation of my transducer... like perhaps there were excessive airbubbles in the epoxy/fibreglass that was used to mount it to the hull. (its a thru-the-hull type) Something is making me feel like that may be the case. The fibreglass around the transducer is a MESSY job! Its all gloppy and just looks like a kid did it.

I would really like to know what everyone thinks because I am bringing my boat back to have the troling motor fixed and I believe this will need attention too. WHat do yall think?
 

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You only need a very thin layer of epoxy, maybe max 1/16" thick in each of two layers, one on the transducer itself, one on the sanded hull. Any more just increases the chances of air bubbles and each one of those either block signals or cause noise. Get the dealer to let you borrow a new transducer to test the setup on the water. First hold it outside the boat, belly aimed down. If the display is clean then put some water in the bilge and put the transducer in the water, look for a clean display.

Jim
 

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Discussion Starter · #3 ·
So if is installed properly it SHOULD have a clean display and not be full of noise? Thats what I am curious of finding out before I drop the boat off at the dealers this morning to be fixed. I think they realize I dont know too much about boats and I want to be armed with as much accurate info as possible so I can get things done correctly this time.
 

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Having to drop sensitivity to 30% isn't acceptable. Dropping to 75% is. My guess is if you drop the boat off to fix that might tie it up weeks or months if they don't know what they are doing or are very busy with lots of folks ahead of you. That's why I suggested doing the test to eliminate the transducer installation. If that's bad then you can re-do it yourself and keep fishing. It's not a big deal to install. But first you need to know what's wrong. Try to borrow a transducer, hook it to the back of the unit, and make sure it isn't the head unit first. They might just re-install it badly again and continue the problem. My guess is they haven't been in business long enough to get the experience.

Jim
 

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Discussion Starter · #5 ·
The dealership, Marshalls, has been in the business since the 60's. However the guy who installed the unit, I found out was only doing this type of work for about 9 months. I dropped the boat off this morning and told the guy in charge how much I was disappointed with their newbie mechanics work.
 

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Discussion Starter · #6 ·
Well I went back to the dealer at lunch t ime to see how far they were getting with my boat. They had the transducer moved. They took it off of the center of the boat which is where they had it. They said that being mounted in the center of the hull can cause problems because of the thickness of the hull at that point. Now it is mounted slightly to the side.. maybe 4 inches or so off center and with some different material than what they used last time.

They also had picked my motor up some on the transom and were in the process of repairing my trolling motor.

I was very happy to see them getting on it so fast. Though I thought it was because of what I had told them and it was something I did on my own... but come to find out... my boss, Joe, went down there and spoke to the owners and that is why they were working on it so hard. Works for me ;)
 

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You shouldn't have noise with the unit set on auto. If you see a lot of suspended dots, they could be dirty water or debris returns. The type of background you were seeing sounds like air trapped between the transducer face and the epoxy. By lowering the sensitivity below 60% you will be unable to locate fish, unless you are in 5 feet of water.
After launching look at the unit sitting still without the engine running. Start the engine and look at the screen, no new noise should be there. Put the boat in gear and idle, no new noise and start running up on a plane while watching the sonar unit (and where you are going) for any evidence of noise. If you start to see surface noise, then the transducer is in the wrong place and picking up hull transfered signals like bubbles. Good luck!
Tom
 

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Discussion Starter · #8 ·
I picked up my boat this evening and they showed me all they fixed. We launched my boat in their pond and the sonar screen was clean as a whistle! It looks so perrrtty! They said the guy that installed it the first time screwed it up but they cleaned the hull, used epoxy this time, and relocated the transducer. It now sits about 6 inches off center in the hull and the noise is gone! :) I will still do what you suggest tho when I get to run it this weekend to make sure i get no bubbles or interference when running the boat. :)
 
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