Depth Sounder Accuracy - SailNet Community
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post #1 of 24 Old 09-17-2012 Thread Starter
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Depth Sounder Accuracy

Given the same depth but a rocky vs. soft (mud, sand, whatever) bottom, is it the case that depth sounders may take different readings?

Will I have a more accurate reading sailing over a hard bottom?

Donna


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post #2 of 24 Old 09-17-2012
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Re: Depth Sounder Accuracy

Yup often inaccurate esp. over mud. Some sounders have a sensitivity setting which you can alter to fine tune things.

Hard bottoms like rock give a good return so should be accurate.
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post #3 of 24 Old 09-17-2012
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Re: Depth Sounder Accuracy

My Airmar works beautifully for sand and mud. I checked the reading in the slip with a weight and line (sandy / muddy bottom) and it was correct to the nearest inch at 10ft.

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post #4 of 24 Old 09-17-2012
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Re: Depth Sounder Accuracy

I've never noticed any difference in readings with a sounder regardless of the bottom but we had invested in some expensive equipment for it's time when we had the the fishing boat.

That's not to say that you wouldn't get different readings depending on a varity of conditions such as manufacturer, transducer location, water clarity, false echo returns.

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Re: Depth Sounder Accuracy

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Originally Posted by DRFerron View Post
Given the same depth but a rocky vs. soft (mud, sand, whatever) bottom, is it the case that depth sounders may take different readings?

Will I have a more accurate reading sailing over a hard bottom?
I would think that the most likely scenario with a soft bottom is that the finder loses it entirely. When this happens, my new Airmar beeps and displays --. My old 1984 model displays 00 (which means infinity in the manual). This has only happened to me passing through turbulent water behind a tug. It's never happened in normal conditions in SF Bay.

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Re: Depth Sounder Accuracy

This all makes sense. Thanks very much.

Donna


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post #7 of 24 Old 09-17-2012
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Re: Depth Sounder Accuracy

I do find it comforting to have two entirely separate finders though. When they are in agreement, my confidence goes up a lot!

The old IMI is definitely flakier than the Airmar DST800, but then that's the reason I got the latter. I've been cruising along and the IMI has read 20 18 16 14 12 10 8 6 4 2 0 0 0 2 4 6 8 10 12 14 16 18 20. There is nothing on the chart. Perhaps a whale?

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post #8 of 24 Old 09-17-2012
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Re: Depth Sounder Accuracy

that ones of the reasons ive deployed 2 depth finders on my boat the old data marine that is the original and a garmin gps/chartplotter/depth finder if they are in agreement i know im fine
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post #9 of 24 Old 09-17-2012
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Re: Depth Sounder Accuracy

I also have redundancy in the form of a fish-finder/sonar unit that displays on my Garmin chartplotter. This gives me 2 depth readings. The FF also gives me bottom info(soft, hard) and fish. Either will give me histories(getting shallower or deeper)

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Re: Depth Sounder Accuracy

Haven't had any issues with soft mud giving a false reading, even though I suspect it has happened more than once. Out west, we had issues with the depth sounder echoing off thermoclines, giving us shallow readings even when there were 100s of feet below the keel.

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