Does anyone else have problems with erroneous readings on a NASA Clipper echo sounder?

Plodding around Poole harbour last month, looking for somewhere to anchor, I was patiently watching the sounder slowly drop to 1.8m before throwing the hook over. Suitably secure, I checked the depth again, still 1.8m so dived off the back of the boat, sluiced through the water, turned around and stood up with the water barely up to my waist! I walked all around the boat with the sounder still showing 1.8m......

Then again, on other occaisions, I've measured 1m on the sounder and prodded the depth with the boat hook and its been spot-on.... so sometimes its right and sometimes it isn't - any ideas anyone?

I dont have any direct experience of the NASA But do you think it could it be the quality of the bottom affecting the echo eg soft mud and weed or hard rock or shingle?

I have owned sounders that gave erratic readings in shallow water but were otherwise reliable at more than 1-2 metres under the keel.

I have found LED sounders useful for ditch crawling. But prefer the digital one for normal depths.

Yes, that had ocurred to me. Every time its given erroneous eadings, its been over a (very) muddy botom. I was wondering if it was reading the rock beneath the mud as the depth...

...its a theory...

If the evidence is that erroneous readings only occur over a muddy bottom I am sure you are right in thinking this is the cause.

I think a problem for digital and analogue meter needle sounders is that the instrument has to determine which echo to use for depth indication and generally they do this well.

I think its amazing that an echo is detected at all from very soft mud maybe made worse by a strong tide carrying suspended mud not to mention the odd fish, so I think they do pretty well really!

In difficult conditions though, I think a human (who probably knows the approximate depth already) can sometimes make a better judgement from the multiple echos shown on the led sounder.