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Old 04-08-2019, 03:21 PM   #1
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Airmar Transducer false low depth alarm

I have a new airman speed and depth log linked via the volvo penta engine management system to a small VP screen then to my Simrad MFD.

When I am at anchor the low depth alarm comes on.

There are three screen shots that show this when the boat was at anchor and hadn't moved. Notice the lat and long don't change, the times are also very close.

Volvo Penta tell me that all transducers are inaccurate above 60m (agreed) and below 10m (30 feet approx). I have had several boats with transducers that are reliable below 10m.

The real depth was 5.6m (sorry about the metric units but they are what we use here)

Any thoughts welcome

Gilbert

PS It wasn't sunny and no big fish were swimming under the boat for shade
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Old 04-08-2019, 08:06 PM   #2
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I have Airmar transducers attached to my Garmin MFDs and 4" displays. The MFDs have the depth alarms turned off, but the 4" displays are set for 2' below the keel. It's extremely rare that I will get a false alarm underway, but at anchor, almost once a night. My guess is fish. Underway the fish probably aren't there long enough to trigger the alarm, but at anchor it's not hard to imagine a fish staying under the transducer long enough to trigger the alarm. It would be nice if you could adjust the duration period to eliminate the fish alarms.

Ted
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Old 04-08-2019, 09:08 PM   #3
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First a bit of history. On my N46, my transducer would display random numbers in shallow water and or tied to the dock. I replaced the transducer, problem gone.
Now, my 2008 AT's Airmar transducer started displaying random numbers in shallow water and or tied to the dock. I do have a secondary, independent, glued-in depth sounder that seems to be accurate.
I had the diver clean the Airmar's face every time he did the hull, no change in reliability. This haul out, I checked the face of the transducer, clean as a whistle.
I had the Airmar transducer replaced. When I get back to the boat, I hope to discover, problem gone.
What I would really like is, a depth sounder forward of the engine room, for poking around in the shallows, knowing at other than minimum speed it would be not be accurate.
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Old 04-09-2019, 08:11 AM   #4
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Quote:
Originally Posted by gilbertpark View Post
I have a new airman speed and depth log linked via the volvo penta engine management system to a small VP screen then to my Simrad MFD.

When I am at anchor the low depth alarm comes on.

There are three screen shots that show this when the boat was at anchor and hadn't moved. Notice the lat and long don't change, the times are also very close.

Volvo Penta tell me that all transducers are inaccurate above 60m (agreed) and below 10m (30 feet approx). I have had several boats with transducers that are reliable below 10m.

The real depth was 5.6m (sorry about the metric units but they are what we use here)

Any thoughts welcome

Gilbert

PS It wasn't sunny and no big fish were swimming under the boat for shade
first, the alarm is coming from your settings/MFD

second, the problem is whether the transducer is providing accurate info. i know plenty of people that think they are in deep water but are over a rock or something. if you are 100% positive it was off by a few meters, i would do two things: a) check the manual for specs to see if it is the right transducer for you and whether there is any troubleshooting or maintenance to be done to try to fix, b) pick a different transducer
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Old 04-10-2019, 04:23 AM   #5
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Just to confuse things more!

The boat was by the side of the house, absolutely no wind, no waves and no current.

The transducer went from 1.8 to 0.4 and back up again.

Changed the transducer from one that went through the Volvo system to a brand new airman straight into the NMEA system. Exactly the same!

I suppose it must be something to do with the Simrad system.

Thoughts welcome
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