Anybody ever seen anything like this before?

There are some areas where there are pinnacles very narrow columns of rock rising to close to the surface. Used to scare the life out of me as OOW on an SSN doing a deep fast passage. North Channel has a lot which is why there is a wire swept channel there
 
You sailed over an SSN. OOW was probably none the wiser until the sonar operator reported your depth sounder pinging.
 
In the Atlantic, I'd say whales.
Could be a shoal of fish.
Or a thermal layer of water.

Or just a marginal 'fault' in the sounder. When it's trying to receive pulses from 140m, it turns the gain right up and is susceptible to small reflections, such as a cabling issue which isn't calibrated out.
 
Sailing in the Clyde we used to see occasionally the depth sounder drop to 5 metres or less in the middle of where 100 metres was expected. I always panicked, took a look round, peered over the side and checked the chart again but never knew what was happening. My guess was fish but I'm interested that someone else had the same experience. I didn't really want to start ignoring sudden drops to detected depth.

I thought it unlikely to be sub because of sub-facts broadcast.

I'm sure locals will come across soon to explain all ...
 
BelleSerene said:
You sailed over an SSN. OOW was probably none the wiser until the sonar operator reported your depth sounder pinging.
Click to expand...

You jest, but as a diver approaching the surface the one thing that was really scary was a yacht under sail. Mobos you can hear miles away, your own dive boat you can tell by the sound of the outboard, but 6ft of lead keel is silent and moves very quickly compared to you.

Now was that echo sounder trace of our subs, one of NATOs or a Russian?
 
Cant see how you would get a trace like that from a standard echo sounder unless its a bottom search or fwd pointing sonar. Maybe I'm just not seeing it right.
 
It may well be what it appears to be!
Many of the small rocky shoals that you see on the surface often drop off their sides 400 foot straight down so it is very likely that there are similar rock pinnacles hidden below the surface.
Only several years ago a shoal which you can stand on was found at the entrance to Plockton bay despite it having been in use for many centuries.
Remember that there are still vast areas inshore up here that were last lead line surveyed in the 1870s!
But of course equally you are traveling through a do not stop submarine excercise area with underwater sensors and who knows what else area in the Inner Sound between Skye and Applecross so a sub pinging you might be whats happening.
Oh and they dont let you know.
I once had my gps jammed on a day when there were no scheduled excercises.
 
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Orla said:
Its just the standard B & G through hull, log, depth & temperture.
Click to expand...
Hummmmmmmmmmmmmmmmmmmmmmmm :) Dont know what else to say or suggest.
Only oddity I can see is what looks like a chain across the top of the pillars which then descends to the bottom alongside the fwd pillar. That's not right. You wouldn't get such clear definition on a commercially available top notch sonar let alone a cheapo echo sounder.
 
Sandyman said:
Hummmmmmmmmmmmmmmmmmmmmmmm :) Dont know what else to say or suggest.
Only oddity I can see is what looks like a chain across the top of the pillars which then descends to the bottom alongside the fwd pillar. That's not right. You wouldn't get such clear definition on a commercially available top notch sonar let alone a cheapo echo sounder.
Click to expand...

Surely the "chain" is just the gizmo trying to link up between soundings to give a picture of the supposed bottom.

I've seen things like this from a variety of sources, for example, a real echo from a sub or a whale or a shoal of fish, a false return from some change in the water - temp and / or salinity, changes in the wake of a vessel which has recently passed over that point. I've also seen instruments misbehaving at particular depths where there has been confusion between which ping's echo is being received: ie the echo is considered to be from the last ping when, in fact, it is a delayed echo from the ping before. Remember, too, that it could be from some combination of unexpected factors.
 
Going by the chart picture (post 10) I wouldn't think it is the sea bed, rock pinnacles, sudden shoals or whatever. I'm based at Arisaig, just a few miles from the position shown and regularly chat with the skipper of the Shearwater which sails daily from Arisaig to the small isles. The area is also well trawled by fishing boats.Ferries to the small isles cross that patch daily as do sail boats, whale watching boats etc. I would have thought it would have been seen and reported by now if it was something permanent. Submarine, temperature change or dare I say, glitch in the echo sounder itself? Or how about a basking shark or sunfish, both of which frequent these waters?
 
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