Depth readings erratic

[gtmoore]

My elderly (9 years) autohelm Tridata which has previously been very reliable, started giving me some odd readings yesterday. Whilst quite happily enjoying lunch tied to a mooring in 8 meters of water, I noticed the unit beeping and displaying 2 meters which then slowly crept back up to 8. This happen several times.

On the sail back, I was tacking down Southampton water and again this happened whilst seemingly still in deep water the unit was temporarily displaying a shallow depth.

Is it possible that fouling on the transducer would cause this? I haven't taken the boat out for about 5 weeks and the log wasn't working either which I assumed was weed as this happens quite regularly. The only time I've noticed this in the past is in aerated water such as when passing over the wash from a large vessel but that really wasn't the case yesterday. Perhaps this a symptom of a transducer unit reaching the end of it's life?


<hr width=100% size=1><font color=blue>Gavin </font color=blue>

 

[snowleopard]

reflections of sound waves by fish, bubbles, bands of colder water or passing submarines can give anomalous readings. i had my depth alarm sound in mid channel last week - set to 1.5m - then revert to 50m reading.

in very deep water like loch ness, i regularly get false shallow readings but i don't believe it's nessie!

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[dralex]

I had a very similar episode cross channel- my unit was reading 1.5m the whole way. Check that the transducer is still bonded to the hull correctly as degeneration of the interface can affect readings. Otherwise it's probably water conditions or things under the water. Isothermal layers in the water can confuse some depth sounders.

<hr width=100% size=1>Life's too short- do it now./forums/images/icons/wink.gif

 

[Capt_Scarlet]

I have a bidata that started to give erratic readings. Rather than being fitted through the hull, mine sits in a vertical tube glassed to the inside of the hull, which should be partially filled with oil. I pulled it out and the face of the transducer was covered in a slime - I wiped it off and added some fresh castor oil (from a chemist). It has behaved itself since, although time will tell.


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[Rohorn]

I had similar erratic behaviour from my 12 year old and usually very reliable st50 tridata, both for depth and speed readings, first wild variations, then a sort of regular fluctuation, alternated with periods of blank screen. Sent the unit to the local Raymarine agent, pronounced the card dead, new unit st60 to cost 535 euros plus Vat. In process of replacing with furuno fishfinder/log at much better price, but time will tell if it will match up long term...Cheers...R.

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[silverseal]

Earlier this summer had a similar problem when moored in Osborne Bay. Put it down to cold water layers, fish, Greman Midget submarines etc. A few days later the system started "shallow water warning". Checked the castor oil interface between the transducer and the hull, found it was near empty, added more castor oil and no more phantom alarms!

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[gtmoore]

Thanks for all the replies. My transducer is a through hull fitting although this seems a shame if the ones attached to the insides are just as good. There is actually is an old transducer fitted in this manner next to the Autohelm one I'm using but the cable has been chopped off (by me - I couldn't see what it was for).

I'm going to jump in and try and sort the log out next weekend (if it's warm enough) so will take a look at the depth sounder fitting while I'm there.

Cheers

<hr width=100% size=1><font color=blue>Gavin </font color=blue>