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Intermittent Depth Indication?

peaman

Sustaining Member
Three years ago, I installed a new B&G DST-810 depth/speed/temperature transducer along with a suite of other NMEA2000 instruments. As others have experienced, the temperature indication failed early on, but the speed and depth have been reliable. Today, my boat went back in the water after its 6-month vacation ashore, and I was surprised to find that the depth indication was not reading normally, sometimes reading a possibly correct depth, and sometimes showing "---". There are two possible explanations for this, and I'd like to get a sense of which, or what, I may need to do.

1. During the time on the hard, on a couple occasions, I turned on the instruments for maybe a couple of hours at a time for the purpose of checking wind and chart plotter function, etc. Since the DST is powered by the network, it too was powered on while out of the water.

2. Today my boat was launched into a small river, in an area which tends to collect silt and organic material. The depth in the marina is pretty shallow, mostly less than 6 feet. This is not my usual sailing area, as my summer base is several miles away.

So I intended to launch today (in pouring rain) on a rising tide, with the intention of heading down river, over reportedly shoaling waters over a sandy bottom, into more open water to my summer berth. But once launched, I saw "---" for depth and chose to pull into a slip pending investigation. Once in the slip, I saw that the instrument would read credible depths like 6.1 to 6.2 feet for several seconds before going blank ("---") repeatedly. I do not fancy the idea of traversing a challenging channel without credible depth information. I have done the trip twice before and both times required "feeling" for the actual channel.

What is the chance that I have ruined my depth instrument by powering it on while out of the water? What is the chance that the intermittent reading is simply due to a soft and indeterminant bottom? Facts, suggestions, anecdotes, and discussion welcome.
 

Prairie Schooner

Jeff & Donna, E35-3 purchased 7/21
If you're at SOTR again, I understand your trepidation. It's a long, winding course with counterintuitive shoaling. No advice, just assurance that you're not being a wimp by wanting to have reliable depth data.
 

Dave G.

1984 E30+ (SOLD)
DST-810 depth/speed/temperature transducer
I believe that Airmar transducer is pretty much the same as a "Raymarine" version sans the connectors ? I have powered up instruments with the Raymarine version a few times on the hard without any ill effect. So my guess it has to be something else causing your issue. My first thought would be to check your hardwire connections and then if you have a backbone unplug and re-plug the transducer wire. Good luck as it sounds like a dicey trip without the info.
 

jtsai

Member III
I have experienced this identical depth sounder behavior every time when visiting a particular creek off the Pamlico Sound. It is a known poor holding ground among locals, soft silty bottom. The instrument reading goes from 6' to "---" intermittently. We know not to anchor there in a blow.
 

peaman

Sustaining Member
I have experienced this identical depth sounder behavior every time when visiting a particular creek off the Pamlico Sound.
This is encouraging. It is also interesting that you and I both report a lowest reading of 6' before going blank. I wonder if that is intentionally designed into the device.
 

jtsai

Member III
This is encouraging. It is also interesting that you and I both report a lowest reading of 6' before going blank. I wonder if that is intentionally designed into the device.
Probably not by design. Mechanical waves such as acoustic and seismic suffer great deal of attenuation and dispersion when propagating through unconsolidated media such as silty mud bottom. Depth sounders are in the KHz frequency range which further amplifies the signal degradation; higher the frequency, faster the energy lose. The "---" probably means no return signal detected, or unrecognizable return signal.
 

peaman

Sustaining Member
Came back to the boat today and sounder is reading correctly. It’s quiet here now, but I guess the bottom disturbance at the lift, and then my own stirring the bottom into the slip caused the intermittency. Consistent readings from 5.1 and now 5.7 on the rising tide. Dropped a lead over the side to confirm depths. I appreciate the support I’ve gotten here.
 
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