And another thing!! Dicky depth readings..

[cliffb]

Out in the Clyde last weekend. Motoring slowly into a bay
14mts of water underneath me... All of a sudden, the depth alarm goes off!!
I have a mild fit. Then ...hey presto, 14mts again. I put it down to a 'glitch'
Next day ...much the same thing. Except that this time I spot a possible pick up bouy and do a hard port turn. Depth alarm goes off again... This time I only have flutters...and lo and behold... it returns to the depth I previously had.
Being a newbie...does this happen on a regular basis? Or could it be due to slow speed...or a chunk of seaweed? Or a dickie transponder?
Any experiences ... thoughts, more than welcomed.
Thanks
BTW. it's a B&G

 

[AngusMcDoon]

This used to happened to me too when I had a cheaper (cheapest) brand of depth sounder. It used to go away pretty quickly like you said, but still annoying.

There aren't many places frequented by boats where the water goes from 14m to maybe less than 2m deep within a boat length that aren't marked by buoys.

Of course there are some, which will now be pointed out to me...

 

[chrisc]

sea weed !!!!!!

 

[Evadne]

Causes of shallow glitches

Anything that reflects sound, actually: fish; layers in the water such as: river outflows, fresh overlying salt (a good one in Loch Etive quite often) or vice versa, stirred up mud, if its thick enough, plankton (though I've only seen that in the deep ocean)..... the list is endless without including submarines and Nessie's relatives. Oh, and nets, wrecks and rocks of course. Especially nets with big fish caught in them.

 

[Peppermint]

Re: Another type of problem

It was foggy in the Solent and I'm looking for the Hamble. Follow the 3m line. No bother. Depth sounder sits on 2.9m all according to plan. Found Cardinal buoy and green withies no bother. Now the channel into Hamble is of variable depth but I've got 2.9m all the way and into the marina. Domestic battery didn't last many minutes after dark. So low voltage doesn't cause a fail safe shutdown on an ST50.

 

[sttpt01]

I found that crossing the wash of the Condor sea cat in Poole harbour would give readings of 1m with my older depth sounder in the main channel. I now have ST40 gear and no longer get any spurious readings.

 

[pappaecho]

Re: And another thing!! Dicky depth readings..

I still have problems with depth sounders on various boats that I sail or own but not both.
The surefire test is to test the sounder transponder directly in seawater. If this does not give spurious readings, then short of Submarines, the cause must be the transmission of sound through the hull.
A sharp turn as you describe, may involve heeling, and hence the most likely cause is how the transponder is bonded to the hull. Some bond directly to the hull with mastic or epoxy, whilst others bond a plastic tube to the hull, and then fill the tube with vegetable oil. The oil acts as a sound transmitter much the same way as it is used in ultrasound tests on pregnant mums. If there is not enough oil, or the transponder moves ( during heeling for example) then duff results will occur.
I debugged a Nasa sounder recently by taping the sounder to a bamboo pole which was suspended over the transom with the head in water. The results were prefect. Back to the pipe and oil routine and the same error messages - replaced the oil with new and the problem was solved

 

[pragmatist]

Fiddling with the gain sometimes helps but changes in the nature of the bottom can cause the problem. We had consistently good results on the E Coast with nice mud but in the Solent resorted to turning it off as all the spurious alarms caused small daughter to have pink fits.

 

[gorb]

Lots of possibilities, many already mentioned. Any turbulence around the transducer can cause misreadings. Favourite time is as you approach a mooring, quick burst astern to slow down and - whoops, no depth (apparently)! Cause is the turbulent water from the reversing prop flowing past the depth transducer.

In the Clyde, it is really difficult (but not impossible) to sail in depths of 2m unless you can touch the trees and rocks by leaning over the side!

 

[mikejames]

I use a fishfinder because just like the old Seafarer it shows what kind of stuff the sound is reflecting off. The wakes of ships cause the sounder to lose sight of the bottom - a trace of a cloud of stuff about 2-3 metres down appears. Other times layers appear in the Solent near river entrances.
In deference to the memory of the Seafarer, I leave the keel offset as 0 and reading in feet .
I use the transducer in a pool of epoxy fixing style.

 

[cliffb]

Re: And another thing!! Dicky depth readings..

Thanks one and all. You've come up trumps...yet again. I shall rest easy from now on.
Happy sailing

 

[dulcibella]

In the Clyde it's probably a Trident submarine.

 

[samwise]

We are currently wrestling with the problem of dicky depth readings on our Navico depth gauge. It will start by giving sensible and believable readings when the instruments are first switched on, but as soon as the GPS fires up the thing goes berserk, displaying a range from 14 to 111 metres and any number in between.Sometimes it settles down -- often after we have started the engine when the wind drops. Then it plays up again. On a recent run back from Ramsgate it behaved properly for a couple of hours, reading approximately the same as the chart. Next time out, back to yo yo numbers. As East Coast sailors this is a pretty crucial instrument and we can't really pin down a reason for this unreliable behaviour. The instruments came with the boat and may even be original (1988). The trouble has only started since we added the chartplotter ( installed at the chart table) and a Silva repeater display on the cockpit panel. Any ideas?

 

[bob_tyler]

Re: And another thing!! Dicky depth readings..

You don't say how the power is supplied but the cause of the false reading could be a low battery. When further instruments are "fired up" the voltage drop to the echo sounder could be increasing.

 

[sailorman]

Nuke Sub outa Faslane /forums/images/graemlins/wink.gif