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Author Topic:   Garmin 498 GPSMAP Sounder
pred02 posted 07-13-2015 06:06 PM ET (US)   Profile for pred02   Send Email to pred02  
Hi. We have a Garmin 498 GPSMAP Sounder on our VENTURA 210 boat. To date the depth finder was working alright, whether when the boat was in motion and still.

Last season we noticed that we would only get a depth reading when the boat is still, and when in motion we would get flashing numbers but no depth reading. We also sometimes get an incorrect reading, usually when the boat is moving slowly.

I tried to re-calibrate the GPS and also move the position of the [SONAR transducer] on the back of the boat, but to no avail.

Is it possible that the [SONAR transducer] needs to be replaced?

The problem is that the boat is in Croatia and there are no certified mechanics on the island that can inspect it. How would you go troubleshooting the problem?


Jefecinco posted 07-13-2015 07:18 PM ET (US)     Profile for Jefecinco  Send Email to Jefecinco     
Recommend you call Garmin. The web site will have the customer assistance number. They respond to email but the telephone is far better.

There is a fair chance your sounder transducer is malfunctioning. Garmin can probably suggest some troubleshooting techniques.

padrefigure posted 07-14-2015 10:41 AM ET (US)     Profile for padrefigure  Send Email to padrefigure     
Also check to see that there is nothing on the bottom of the boat that would create turbulence ahead of the transducer. If the system worked before, but is not working now, something changed. Perhaps a clamshell fitting is knocked loose or something changed in the transducer mount itself. I have a Garmin unit that I switch between boats and the older transducer can sometimes tilt up when backing down hard. If you have electrical connection, I would look for something mechanical, first.
n1ywb posted 07-14-2015 10:47 AM ET (US)     Profile for n1ywb  Send Email to n1ywb     
I agree with padrefigure. Check the transducer. Make sure it's aligned properly. Make sure there's nothing creating a flow of bubbles under it. Make sure it's actually in the water when you're under way. Any amount of air under the transducer will screw it up and it's common for various things to cause that when under way.
jimh posted 07-17-2015 04:35 PM ET (US)     Profile for jimh  Send Email to jimh     
I tried to re-calibrate the GPS...

I don't think you can perform any calibration of the Global Positioning System. The Air Force of the USA takes care of that. It is also unlikely you can perform any calibration of your individual GPS receiver. The manufacturer embedded the algorithms used to calculate position in the receiver, and you cannot change them.

...and also move the position of the [SONAR transducer] on the back of the boat, but to no avail.

The inference I am making from your description is your SONAR transducer is a transom mounted type.

If your depth sounder only gets a bottom echo and a valid reading when the boat is not moving, the most likely cause is the position of the transom-mount SONAR transducer. Many mounts have a tilt break-away, and the transducer could have been moved out of the normal position. This can easily be determined by visually inspecting the transducer and its orientation to the hull bottom.

It is also possible that the transducer has begun to fail and has lost either transmitted signal level or lost received signal sensitivity. The bottom echo signals are weaker when the boat is moving, and might be lost if either condition has occurred. There is no way to easily verify this, other than comparison of the bottom echoes you see from your boat's transducer compared to a new one.

If you have any doubt about the integrity of the SONAR transducer, and the boat is located at some distance in a foreign land, perhaps you can buy a new transducer, carry it with you on your next visit to the boat, and have it available for testing or replacement of the existing transducer. I suspect it will be much simpler to bring a spare transducer with your than to have one sent in, but I don't know the procedures for clearing customs when entering Croatia.

jimh posted 07-19-2015 10:02 AM ET (US)     Profile for jimh  Send Email to jimh     
I tried to re-calibrate the GPS...

Even interpreting your comment as meaning you tried to re-calibrate the depth sounder, I still don't think you can perform any sort of calibration of the depth sounder. To calibrate a depth sounder you would have to modify the way it measures water depth, and that is by measuring the time between transmission of sound and reflection of that sound from the bottom. The depth sounder assumes a certain speed of propagation of the sound through the water, and uses that and the time to compute distance. I do not recall seeing any depth sounders that offered an adjustment of the speed of propagation of sound through the water. While I am not very familiar with the depth sounder in the GARMIN 498 GPSMAP Sounder, I doubt it offers a depth calibration function. About the only means to alter the depth reading of a recreational grade depth sounder is to enter a keel offset, if the sounder offers that function. Changing the keel offset would not tend to affect the performance of the sounder when underway compared to at rest.

jimh posted 07-19-2015 11:34 AM ET (US)     Profile for jimh  Send Email to jimh     
Re the problems of sending some spare part from the USA into a foreign country and getting through their customs: it was not that long ago that you could not easily send material like spare parts between the USA and Canada. I think most of these troubles went away after the North American Free Trade Agreement was adopted.

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