Depth sounder accuracy

[Spuddy]

I have a NASA stingray whirlygig sounder. I was thinking of changing to a digital read out device. If I keep the transducer there's a thing about frequency compatibility which I'll look up later.
However the existing thing only gives a decipherable reading to about the nearest metre. Which makes me wonder how accurate the digital ones are - just cos it says 1.96 can I believe it? After all its innards are trying to fill up the decimal places because they are empty.
Would an up to the minute transducer be any more accurate?
Any deep thinkers on the forum?


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[nickjaxe]

We have a lowrance X25 buget type if it say 3ft when we are comming back into the beach its spot on ect ect.

Nick.

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[john_morris_uk]

It depends where you measure the bottom from? Sometimes in soft mud, the echo is from the firmer stuff a little way down from the surface. One of the advantages of the old whirly echo sounders was that you could see a 'spreading' of the return when the bottom was soft. You might argue that its only the hard stuff you are interested in - and our digital one is usually spot on!

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[LadyInBed]

Digital ones have advantages such as:
Switching to feet when you get to read less than half a meter below the keel. /forums/images/icons/shocked.gif
An indicator to show if the bottom is rising or falling.
Easier to read in sunlight.


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[VicMallows]

Changed to a NASA duet this season from the old rotary Seafarer and am most impressed. Seems spot on, and certainly within 0.1m. One slight disadvantage is that you can only set an offset to read below keel .... not below surface. Believe the dedicated sounders allow either. The transducer on the duet by the way is 150kHz, same as most of the old ones (in my case it was the transducer that had packed up).

Vic

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[AndrewB]

Accuracy

I have an old ST50, which I check at least once a year against a lead line for depths up to about 15m. Once the primary offset has been made, it has always been accurate to 0.1m (around 4") up to 5m, at 15m it is a little less accurate.

It is important to set the offset. The easiest way (IMHO) is to drive the yacht gently aground - preferably on a rising tide - and set it to zero, then you have depth beneath keel. If there are further inaccuracies against a lead line, but the unit is reliable (i.e. always reads the same at given depth even if not correct), then I would prepare a deviation curve as for a compass. Above 5m though, small inaccuracies are generally not very important.

 

[Alex_Blackwood]

Yes Digital sounders are accurate.
Yes you can use the existing transducer if it is frequency compatible.
All the clever stuff is done within the electronic box, the transducer receives all its timing and pulse transmit/ receive information from the electronics. Therefore a transducer is a transducer, designed for a set frequency range, or ranges, some sounders will switch frequency with depth range.
The one problem you could have without knowing about it is that the transducer winding insulation has degraded with age and may affect the power output of the transducer. It is possible to test it but you need a "MEGGER" or similar voltage injection device to check the insulation resistance.
Having said all that. If it is the correct frequency then connect it up, set up the sounder and check the readings with a lead line and if it works you are in business !

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[charles_reed]

It\'s easy enough to do

if you know the transducer position relative to wl.

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[Trevor_swfyc]

I have the dedicated Nasa Clipper, which I have set up for actual water depth and as said before the readings are very accurate. What is worth mentioning is just how technology has moved on, no more false alarms from fish as the unit can be set to ignore these false readings. The alarm function is an intermitant buzz that is very loud and cannot be ignored, when going into a shallow anchorage it announces your arrival to all. The Nasa Clipper gets my vote on cost and its large clear display. Once the unit is set up it is worth checking the aground reading by deliberatly running aground in soft mud, then make no mistake when it reads that number you will definitly be aground.

Trevor



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