Transducers

[single]

I fitted a second depth sounder yesterday which is spot on, so while i was at it i thought i would re bed in the old echo sounders transducer. Before, the old one was giving silly readings jumping between 30' to 180'.Its not as bad now and gives a steady 30' but the actual depth should be 15'.Why is this? Surely if its reading then its working so is there some simple reason on the different readings from the new one and old one?

 

[john_morris_uk]

I fitted a second depth sounder yesterday which is spot on, so while i was at it i thought i would re bed in the old echo sounders transducer. Before, the old one was giving silly readings jumping between 30' to 180'.Its not as bad now and gives a steady 30' but the actual depth should be 15'.Why is this? Surely if its reading then its working so is there some simple reason on the different readings from the new one and old one?

Its bouncing off the bottom and off the bottom of your boat and back again which gives a doubled reading. Most modern echo sounders have and automatic gain control. The old whirly ones had a manual control you had to adjust otherwise you got the same effect - but much more obvious visually...

 

[Seajet]

The modern depthsounders I have used do have auto gain, but do have a manual override; but it's a pain to adjust pressing a couple of buttons at once then setting the gain in digital steps, in my experience.

Things like this make me miss the old whirly displays, where gain was easily adjustable and the nature of the seabed easily discerned; but they were noisy and could lead to heart attacks when the depth / reading went just over the dial limit - so readings jumping from 59' to 1' had to be regarded philosophically -and used a lot of electrical power.

I have found fitting a fishfinder as the second unit has given me back the info I missed ( and more ) compared with the simple ' take it or leave it ' digital display depthsounder; if I could only have one it would certainly be the fishfinder.

 

[single]

The modern depthsounders I have used do have auto gain, but do have a manual override; but it's a pain to adjust pressing a couple of buttons at once then setting the gain in digital steps, in my experience.

Things like this make me miss the old whirly displays, where gain was easily adjustable and the nature of the seabed easily discerned; but they were noisy and could lead to heart attacks when the depth / reading went just over the dial limit - so readings jumping from 59' to 1' had to be regarded philosophically -and used a lot of electrical power.



I have found fitting a fishfinder as the second unit has given me back the info I missed ( and more ) compared with the simple ' take it or leave it ' digital display depthsounder; if I could only have one it would certainly be the fishfinder.

I'll try playing with the gain later.They are both digital fishfinders.Another question....originally i was going to make the old one redundant but now i might keet it but would running two with the tranducers 12'' apart cause problems?

 

[Seajet]

I now have two sounders as mentioned; when I first fitted the second one I had the old style transducers ( LCD displays but DS not fishfinders ) in oil baths about 3' apart laterally, each side of the forward hull.

There was indeed interference, if both were on one display would freeze - but the other kept working.

So when I went to a fishfinder for the saloon sounder I moved the transducer to the after hull, behind and just to one side of the keel.

As it came with the transom type transducer I had taken advice from these forums and fitted it inside the hull, simply stuck down with silicone sealant.

It works very well, and the fishfinder display makes up for the nanoseconds' advance warning I have lost by having the transducer aft !

 

[single]

I now have two sounders as mentioned; when I first fitted the second one I had the old style transducers ( LCD displays but DS not fishfinders ) in oil baths about 3' apart laterally, each side of the forward hull.

There was indeed interference, if both were on one display would freeze - but the other kept working.

So when I went to a fishfinder for the saloon sounder I moved the transducer to the after hull, behind and just to one side of the keel.

As it came with the transom type transducer I had taken advice from these forums and fitted it inside the hull, simply stuck down with silicone sealant.

It works very well, and the fishfinder display makes up for the nanoseconds' advance warning I have lost by having the transducer aft !

All your setup is exactly the same as mine then.Could weed on the hull be messing up the readings?

 

[Seajet]

single,

going back to your original post, if it's reading exactly double the depth it does sound as john_morris suggests, the signal may be bouncing twice; is the seabed at the time hard and reflective like rock, or absorbent like mud ?

I think playing with the gain may well be the answer, certainly what I'd try first.

 

[srm]

OP sounds very much like a second return, but the second return will have a lower strength than the first as it has travelled further and been reflected twice, which makes me wonder why the set missed the first return. When using powerful paper trace echosounders I have seen second and third returns. On the old whirly type a second return could give a false shallow reading if it came shortly after the next outgoing pulse. The answer was always to reduce the gain and so loose the weaker returns.

Running two sounders with transducers close together will work if they use different frequencies. If on the same frequency each set may be receiving returns from the other and giving false readings.

In simple terms the circuitry in a sounder converts the time between transmission and first return into depth using an average speed of sound in salt water. Having two transducers transmitting on the same frequency but at different timings will cause a mixture of returns and the risk of false shallow depths being displayed when set 1 picks up a return from set 2 before its own return arrives.

 

[single]

OP sounds very much like a second return, but the second return will have a lower strength than the first as it has travelled further and been reflected twice, which makes me wonder why the set missed the first return. When using powerful paper trace echosounders I have seen second and third returns. On the old whirly type a second return could give a false shallow reading if it came shortly after the next outgoing pulse. The answer was always to reduce the gain and so loose the weaker returns.

Running two sounders with transducers close together will work if they use different frequencies. If on the same frequency each set may be receiving returns from the other and giving false readings.

In simple terms the circuitry in a sounder converts the time between transmission and first return into depth using an average speed of sound in salt water. Having two transducers transmitting on the same frequency but at different timings will cause a mixture of returns and the risk of false shallow depths being displayed when set 1 picks up a return from set 2 before its own return arrives.

I played with all the settings again and now the old one is reading around 30' to 60' and the new (correct) sounding is steady 15-16'. Maybe the old one is just knackered!

 

[alahol2]

Is it possible to swap the transducers to see if the error follows?

 

[single]

Is it possible to swap the transducers to see if the error follows?

Not between the two i have. I suppose it might be worth looking out for an old one.I'll dig out a picture or model.
Lowrance X40 spares are repairs needed! May as well have it working as its in the hole.
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