Gotta ask a question............(not a rant or meant to offend!)

pau1gray

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As a training manager for a leading SONAR positioning company I sometimes sit in wonder in these forums as to what people are actually trying to achieve with their echosounders.

As a boater I can fully appreciate that in water depths of lets say 30m, depth is very important.

As people go into deeper water then of what importance is the depth read from the echosounder?

If for instance the maximum range from the system is reduced by 10%, say for instance by using the wrong oil around the transducer / using epoxy / blue tack etc to mount the transducer, then why is this such an issue?

If the depth reading needs to be correct then how do the bog standard off the shelf systems account for changes in the sound speed through the water column and from area to area? Also what happens if the transducer is not vertical then how is this accounted for?

Like I said it's not a rant or pointing fingers - I'm just interested in knowing why people feel it is such an issue?

/forums/images/graemlins/confused.gif
 

Norman_E

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The only reason I like to see my sounder giving me a reading at greater depths, is that it reassures me that it is working.
For what its worth it usually gives up somewhere between 65 and 80 metres.
 
G

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Ditto. First symptom of my depth sounder expiring was erratic readings at the greater depths. Apart from that, no reason, and depths at the deeper end rarely seem to correspond to the chart...
 

Kawasaki

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Agree ,it doesn't matter in deep water less Your a Fisherman trying to find a wreck or summat! Or maybe a diving bod. Don't know cos I aint one.
Fairly accurate depth is needed for ditch crawling or taking a short cut over a sandbank maybe?
Nice if You have a "forward looking" one.
Usefull in deep water maybe if You are using the depth to check navigation from a chart, like "Am I in the right place there should be 30 metres hear why is there only 20"? etc.
Nice to have an alarm set for a certain depth, depending on how much You draw.
Peeps Do Worry about oil types.
Cos if they don't know they want to put the Right Stuff in, with all the bullsh*t about oils in engines, heating systems, transducers!, cooking, gearboxes, hair oils, massage oils, whale oils.
I mean what type of oil do yer stick in yer avaerage Whale? /forums/images/graemlins/grin.gif /forums/images/graemlins/smirk.gif
 

Searush

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Only time e-sounder accuracy is vital is in shallow water - especially with waves! When looking for ridges/ channels etc in deep water, then relative change will do. It's difficult to be sure about tide depths when the range is 22-33' plus weather fluctuations anyway.

It's easy enough to check the reading when she lifts off the bottom of a drying mooring and thus get an accurate calibration for future mudhole creeping. but my e-sounder is a 1972 "LED on a spinner model" with feet & fathoms ranges! It works for me so why change it?
 

Clyde_Wanderer

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I would prefer to ensure that the correct amount of oil was in the mounting tube than to take a chance on the unit not giving correct readings when most needed.
Its not a huge task to check it regularly and if the correct amount is in it in the first place then it will be easy to see if it is droping over time.
BTW what is the correct amount, ie, over the TD or just covering the bottom of it, and how close to the hull should the bottom face of TD be?
While on the subject, How far out of the hull tube should the log paddle wheel protrude?
 

pau1gray

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Sound does not travel through air as well as it does water. You could use water around the transducer but it may freeze and damage the transducer or it might evaporate, therefore using oil is the best of both worlds.
There needs to be enough oil to cover the face of the transducer (as a minimum) to avoid any air gap so more than that allows for a bit of leakage / evaporation.
The use of epoxy to fit the transducer also has problems if air bubbles are trapped in the epoxy as the air will attenuate teh signals.

Thanks for coming back to me with answers though :)
 

MoodySabre

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On Yachtmaster we were told to use depth as one of the items to check actual position. Obviously this is more useful at depths below 30m when working along a contour can be a means of navigating in poor visibility if GPS packs up. Beyond that it is merely a comfort factor. Being an east coaster then small numbers are more usual - sometimes starting with a decimal point!
 

kengill

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I would have thought as a training manager for a company you would be aware that slight misalignment of the transducer is completely irrelevant 'cos the sound radiates from the plate - it doesn't all go in a collimated beam.
 

Lakesailor

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The weed on Windermere can be so thick that you sometimes have a negative reading. The weed grows about 4 ft tall from the bottom so coming into jetties can be daunting. I was calmer before I installed the echo sounder..
 
A

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I think that it is an issue. As someone else pointed out, depth gives you an idea of your position. For example, an alarm on the 100m or 50m contour will give you warning that you are approaching a coast - e.g. crossing Biscay. Of course we all have GPS and many of us have radar, but depth is a primary instrument and it should be accurate.

In any case, we don't buy expensive measuring devices so that some dickhead can degrade the performance by 10% for the want of using the correct oil. The idea is not far from preposterous.
 

Richard10002

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Some people are very particular about things, and others can be a bit "seat of the pants", so you will get all sorts.

Over a certain depth it becomes academic. On occasion crossing Biscay, or the Atlantic towards Madeira, we have had readings of 3m. I cant recall where mine begins to fail, but it's deep enough not to matter, and I guess it's because the signal isnt strong enough to bounce back from 6000m, or maybe it hits a thermocline, or a big fish, or a submarine.

I want it to work from about 30m to say 4m or 5m for navigation, e.g. corellating a position, or following a contour, and below this to stop me going aground. It's also something to look at when there's nothing else to do /forums/images/graemlins/smile.gif

I didnt even know there was oil in it!

This forum just keeps on giving me more and more stuff to think about and maintain - cant bloody keep up!

What kind of oil should you use, and where does it go?
 
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Richard, suppose I could make a case that you didn't really 'need' your nice new Rolex to be more than, say, 30 seconds accurate, would you be happy for Rolex repairers to be advised that in future they needn't bother to calibrate them /forums/images/graemlins/wink.gif

The issue here isn't whether anyone 'needs' a certain accuracy but whether a precision instrument may be installed in such a way that its performance does not meet the design and manufacturer's spec. Surely that has to be wrong and resisted, particularly when we are feeding back our views to an industry rep.?
 

Richard10002

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I see what you're driving at, but even on commercial ships, we didnt worry too much about deep depths being accurate.

So I guess I dont expect precision from a depth sounder above a certain depth... for me that's about 30m.

When you get down to 1m to 5m, i hope it's reasonably accurate, but I'm conscious of the limitations due to waves, speed of sound in different water densities, thermoclines, double bounces, and so on, (cant remember any more).

But I want my watch to be accurate so I dont have to keep changing the time.
 

blackbeard

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[ QUOTE ]
As a training manager for a leading SONAR positioning company I sometimes sit in wonder in these forums as to what people are actually trying to achieve with their echosounders.
....


If the depth reading needs to be correct then how do the bog standard off the shelf systems account for changes in the sound speed through the water column and from area to area?
/forums/images/graemlins/confused.gif

[/ QUOTE ]
Very simple, as has already been discussed - we are trying to do two things: navigate (using depth as a rough check on position), and be aware of when we are in danger of running aground.
The first of these doesn't require great precision (ie in about 20 metres, we would like an answer within a metre or two), and the precision in shallow water is regularly, as it were, checked.
As a matter of interest, just how much difference does temperature, water composition etc make? I can't recall this ever having been an issue in practice - is the error going to be more than, say, a few per cent?
I suspect that reliability is going to be a greater issue than accuracy - we don't want something that tells us we are about to run aground when we are not, or vice versa. But as to whether the true depth is 20 metres or 21, we don't really care.
It's a very different game, I suspect, to sonar positioning, where I assume you want precision.
 

ccscott49

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As far as I'm concerned, anything over 30 meters is meaningless to me, apart from maybe navigating along a depth contour. I use mine for depth for anchoring and not running aground. I guess some peeps need it for fishing, but not me.
 

Clyde_Wanderer

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Just to recap on the questions I asked in my last post above but got no answers.
How much oil should be in the tube? and how much should the log paddle prutrude out of the hull tube? its a Nasa paddle unit. /forums/images/graemlins/confused.gif
 

Searush

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The paddle unit is your speed log. Depth transducers can be thro' hull (like mine) which is detectable on the outside by a small circular mark which is the sender rather than GRP! Others are mounted against the inside of the hull, sometimes inside a short tube with a layer of oil to eliminate large changes in "resistance" to the sound pulse as it passes thro various air/ GRP/ water bondaries. The oil is similar to GRP/ seawater and thus minimises losses to the signal.
 

Danny Jo

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I am relieved by Searush's clarification. I have a through-hull tranducer, which I removed during the winter (for ventilation, and to allow stray gas to escape). When refitting it I noticed that, in addition to an O-ring seal, it was slightly greasy, so I added a dollop of silicone grease below the O-ring. No chance of changing it now without taking a lot of water on board!
 
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