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DST810 false depth readings  

 

Stiggy
(@stiggy)
Active Member
Joined: 2 weeks ago
Posts: 4
November 18, 2020 10:39 am  

So we recently installed a DST810 and I'm seeing some odd behavior. Temp/Speed seem to work normally. Depth however seems to revert back to 15ft somewhat randomly. I've tracked this with my signalk/grafana setup but also viewed in the Airmar Cast app as well as the N2K Analyzer. Any insight into why this might be doing this as well as what I can try?


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Steve Mitchell
(@stevemitchell)
Member Moderator
Joined: 3 years ago
Posts: 99
November 18, 2020 12:02 pm  

I have two DST810's and have had issues with one of them since install. If you search on various forums or just the internet in general, you'll find people having similar issues for a number of years. I'm involved in a forum thread on TrawlerForum about flaky depth and speed readings, etc. that you can probably find. Mine show up as DST200s in NMEA 2000-land as well, which is irritating.

However, it doesn't necessarily mean that your sensor is dead or broken just because it is showing weird depth. It could be thermoclines in the water, reflective junk, or a number of other reasons. Mine routinely will show 6 feet depth for 5-10 minutes and then go back to showing actual depth, and it is clean (I've removed it many times) and there are no other issues that I know of configuration or location wise. 

There are some spots where I've found this to happen reliably, over and over, and I assume it has to do with the water or the bottom, and that the sensor just can't read it. Those spots I know I will lose accurate depth. But it also happens randomly in places which is the irritating part.

I've also looked at alternatives, and there aren't any. Airmar is really the only game in town, and the ultrasonic stuff seems like it has its own set of problems. I'd be curious if you are able to correlate specific areas that have issues, or if it is something that just goes haywire, like mine, in random spots as well.

Editor, SeaBits.com


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Steve Mitchell
(@stevemitchell)
Member Moderator
Joined: 3 years ago
Posts: 99
November 18, 2020 12:55 pm  

Yikes that is a lot more than mine does. Is this brand new? Did you make sure they didn't paint it with your recent bottom job? Mine had some paint on it from my yard time in August, but that didn't seem to make a difference once I cleaned it.

Editor, SeaBits.com


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Steve Mitchell
(@stevemitchell)
Member Moderator
Joined: 3 years ago
Posts: 99
November 18, 2020 12:55 pm  

Oh and just to be clear, I have the 810 and 800 - one of each. That was a typo....

Editor, SeaBits.com


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Stiggy
(@stiggy)
Active Member
Joined: 2 weeks ago
Posts: 4
November 18, 2020 1:03 pm  

@stevemitchell

Yup brand new. It appeared to be clean when i looked at it while it was still on the hard. I didn't check it just before we splashed. I guess I could pull it up and take a look. Just checked the temp graph and that seems to be working fine. 


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Peter Haeussler
(@peterh)
Active Member
Joined: 1 year ago
Posts: 9
November 20, 2020 12:31 pm  

This thread grabbed my attention as I'm planning to buy a DST810 in the near future. But, I think Steve is right - its probably related to thermoclines. Maybe the 810's internal software is not quite as good at filtering out thermoclines as others? That said, I do a fair amount of marine geology research, and the thermoclines in the ocean are impressive - particularly at shallow depths. We commonly do CTD casts (conductivity, temperature, depth profiles) to get better water column velocity data to make better maps of the ocean bottom. Attached is a CTD cast (randomly grabbed off the web) showing how temperature and salinity varies near the sea surface. Such layers give rise to reflections and can fool the depth sounder. 

1605893515-Screen-Shot-2020-11-20-at-82605-AM.png

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Stiggy
(@stiggy)
Active Member
Joined: 2 weeks ago
Posts: 4
November 20, 2020 1:06 pm  

@peterh

Interesting information. I will see if it does it while we are underway. I also just installed a BBDS1 with an airmar 744v transducer and it works flawlessly. 


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