Help with nasa depth sounder

[webcraft]

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Mine has always been inaccurate in water over 60m, less than that in some conditions. Always OK in 30m or less, so it really doesn;t bother me. As neafrly everyone has a chartplotter this shojld indicate if the spurious readings have any credibility.

The idea that you might want to follow a depth contour of 50m or more seems a little unlikely.

- W

 

[Bergamot]

I had a leaky tube so the oil drained into the locker causing a mess. On old sea-salt said he did not use oil, just a some plasticine in the tube with the transducer pressed into it. I thought I would try this to see if he was pulling my leg. 5 years on it is still working perfectly.

 

[PaulRainbow]

If you use the tube, fill it with anti-freeze.

You can also bin the tube and stick the transducer to the hull with slow drying epoxy, taking care not to trap air bubbles.

 

[Stemar]

Mine's stuck to the inside of the hull with the Gosport pound shop's equivalent of No More Nails. I had to redo it a couple of years ago, after about 10 years.

 

[Amulet]

I have the impression that it goes round the clock at 100 metres, i.e. 110 reads as 10. Surely I can't be right. I did used to get weird reads in shallow water when the bottom was squidgy on the east coast. Now in Scotland with a firm bottom it seems fine.

 

[ghostlymoron]

Mine was a bit iffy in shallow water with a sandy bottom. I put it down to suspended particles giving an echo. That apart, I never had problems.

 

[Pikor]

https://www.nasamarine.com/faq/

Have some suggestions about erratic readings.

 

[Rocksteadee]

The signal is a timed ultra sonic pulse reflected from something.
This can be air bubbles in the oil or epoxy, hopefully the sea bed but can also be layers of different density and temperature water normally only found when in deeper water.

I have heard a story of a boat whilst off the south coast in quite deep water, to have the depth gauge jump to a shallow 10m and stay for a few seconds. After the ensuing panic of an unseen rock a periscope appeared a few yards off then disappeared again

 

[Daverw]

I would expect most to struggle in deep water, assume the deeper the water the stronger signal needed to be sent to get a clear return. Perhaps the NASA and others does not have the power or sensitivity to measure deep.

 

[Stemar]

The signal is attenuated by water and, especially stuff in the water, be it plankton, suspended mud or whatever. Any sounder fitted to a yacht is going to run out of steam sooner or later. The other problem is the time between pulses. If the water's deep enough for the second pulse to be sent before the first one gets back, the sounder's going to get confused and give spurious results.

As long as I know the depth reasonably accurately when I get down to 20m or so, I'm happy.