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Becoming an Amateur : Part 3

Could you find a machete thrown into a river using sonar?

Hopefully we’re back on track now. Having to reply to that ridiculous open letter shouldn’t have been necessary but one intriguing thing did emerge – could be a false dawn but the trolls seem to have dialled it down their messing with Wiki so perhaps someone has woken up to just how bad that looked.

That said, I was sent a short appraisal of a post by troll in chief that basically amounted to a last desperate attempt to convince anyone who would listen that people knew where the wreck was.

Who cares? We weren’t the first to find it, John Futcher’s crew did that.

Troll’s new version went something like, the ‘coordinates’ were with DMC’s lawyer from the get-go. Well, they weren’t because his lawyer was Lord Victor Baron Mishcon and I had many dealings with him and he didn’t have a clue. Ken Norris would certainly have known had these alleged coordinates existed and would definitely have shared them, but he didn’t know either. Then there’s the question of ‘coordinates’ themselves. You only have to read of the navigation competitions between the RAF and the USAF during the Cold War to realise that the best of the best locked in competition could only manage accuracies of several hundreds of metres on a good day and more usually several miles. No use for finding tiny shipwrecks.

The second part of Troll’s claim is that the local divers also had these coordinates years before we turned up. That would be why they came and asked if we would share the position then, but let’s ignore that and assume that everyone and their cat had these ‘coordinates’ but weren’t letting on.

Therefore, our mission was, with no help from anyone, to find the wreck of K7 from a standing start, and we did. The challenge was the same either way. But it doesn’t stop there. It’s even more definite that no one knew where Donald was and, as an underwater target, he was in a league of his own in terms of difficulty. Yet we found him too, and so accurately that we were able to return again and again to carry out the Coroner’s instructions.

So, troll, just so we can put this to bed once and for all and make sure the historical record is 100% accurate, here’s your challenge. Seeing as there’s now nothing down there, the ‘coordinates’ are of no use to anyone, go get a copy from the divers, or whoever told you they existed, and publish them. Once I have them I’ll see just how accurate they are and we can confirm whether anyone did know. It would make for an interesting exercise so, over to you.

Right, where were we?

Back to the three points.

  1. Everyone knew where the wreck was. We’re waiting on Troll and his ‘coordinates’ to bottom that once and for all.

  2. The equipment we used was widely available and nothing special. I think we’ve answered that.

  3. Any divers could have done what we did.

That’s an interesting one. In theory others could have done but none did. I mean, we could have learned to play musical instruments instead and been the Beatles – but we didn’t. Nor did we know of another dive crew with anything like our technical capabilities. Every diver, every dive boat or angling skipper we knew seemed happy to dive or fish the same wrecks time and again but once it became known that our crew was finding new targets some would ask if we knew where this or that wreck could be found because we spent more of our time searching than diving and that just wasn’t what anyone did then.

You didn’t kit into your drysuit to go out on the boat all day to run up and down in straight lines burning through fuel with the mag going, beep, beep, beep for hours on end. It just wasn’t a thing. And sidescan is even worse. That needs an alert crew who all know what they’re doing and a moment of distraction can have disastrous consequences.

I won’t bore you with all the various disciplines we’ve used over the years but I will give a brief explanation of my favourite – sidescan sonar.

Sidescan is a form of acoustic imaging – creating images using sound rather then light. Sound travels well through water, light doesn’t. If you’ve seen images of Titanic you’ll know that even with the most powerful lights you can still see only a bit at a time.

But creating images with sound is a different matter. Compared to light, sound is incredibly slow so you have to work with this. Essentially, what acoustic imaging does, is fire a beam of sound into the water in the direction you want to look then wait to see what comes back as an echo. These ‘pings’ are then used to produce an image line by line rather in the way of an old TV set, and it gets very demanding when taking pictures of shipwrecks or finding small targets.

With sidescan the equipment to put sound into the water is in a torpedo-like vehicle towed behind the boat on an umbilical – it’s called a towfish. The umbilical supplies power and brings data to the surface and towing the fish is where the trouble starts.

To get good imagery you need to tow at constant speed because the software assumes this and allows for how much the fish should have moved between the sound leaving and when it’s expected back so if it comes back and the fish hasn’t gone as far as expected, whatever you’re imaging will get squashed up shorter than it really is. Likewise, if you go too fast your target will get stretched out.

If you don’t drive in a dead straight line your shipwreck will be banana shaped and if you change the fish height partway through it just ruins it completely and if you’re searching for something rather than imaging a known target the navigation has to be extremely precise to make sure you don’t miss it.

We would use a three-person crew. The skipper, whose job it is to drive in straight lines at constant speed and manage the navigation to ensure the boat is where it’s supposed to be at all times. The sonar operator, who keeps the towfish out of the lake/seabed and ensures the correct amount of sound is in the water at all times – and that can be a very dynamic situation because sand, rocks, shipwrecks and mud all do different things when you fire sound at them and you can easily have all four in the same place.

Then there’s things like in estuaries where fresh water meets saltwater and due to the different densities the two won’t mix. It’s called a halocline and try shooting sonar through it!

The third crewmember is out on deck in charge of the winch and to watch for hazards like lobster pots other vessels and even land ahoy if the others are too engrossed in their screens. Either the skipper or sonar operator can shout at the winch operator to get the fish out of trouble but if all is going well only the sonar operator will ask for up or down in order to optimise the data coming up the string.

The fish is dropped into the water and winched down to a height above bottom determined by the sonar operator but the amount of cable needed is a function of water depth because the fish is always going to trail behind and the deeper the water the further back will be the fish before it reaches the correct height because of water drag on the cable. This is called layback and here is where it starts to become a multi-dimensional mind puzzle. Suppose you’re travelling with the tide. The whole water column is pulling the boat and the fish along so you don’t need as much cable but turn around and start fighting the tide and it wants to pull the fish backwards away from the boat so more cable is needed that way or it kites upwards towards the surface – the layback is greater on the return run. Then there’s the turn at the end of each run. You can’t just turn on a sixpence and head back because the fish will immediately crash to the bottom with all that extra cable paid out so the turns are often longer than the line you wanted to survey and having made the turn you need enough of a run-up to arrive at the start of your next line with the fish settled. It’s no good trying to correct the problem once the line is begun. Get it wrong and you need to do that line again.

And what if your lines aren’t exactly aligned with the tide? The fish will be pushed sideways so it’s not directly behind you – offset. Then the wind can play havoc too. It does as it pleases and joins with the effect of tide. No tide in Coniston water but no shortage of changeable wind on any day of the week.

Then there’s bottom topography. If the lakebed is falling away, as it does on a N-S run in Coniston, it’s necessary to pay out more cable as you go and retrieve it on the way back. The sidescan also does what it says on the tin – it looks sideways. It can’t see straight down so there’s always an area beneath that’s invisible, think of the view from a passenger plane. The way around this is to plan your lines so that on the way back you cover the area that was invisible on the last pass. Mowing the lawn, but when you mow the lawn your lawnmower isn’t on a hundred metres of wire behind you somewhere unseen below being pulled hither and thither by forces also unseen while the wind blows you around up top. It’s not easy!

Then, having gathered the best possible data, and you’re looking at many hours to cover quite a small area if you’re after a small target, it’s as many hours again later with powerful post-processing software to mosaic it all together accounting for layback and offset and changes in topography until you have an image you can use.

Then there’s another thing and let’s take the search for K7 as an example.

Sound may travel well in water but it won’t go on forever. It is attenuated eventually and this is a function of frequency. The lower the frequency the further it will go but due to its greater wavelength the resolution becomes poorer. High frequencies will shoot way more detail but only travel a fraction of the distance so there’s a compromise to be made.

If you’re looking for tiny bits of smashed wreckage you need high resolution and that means high frequency and that means much tighter navigation. In 2007 we shot the whole K7 wreck site with 675Khz sonar and our lines had a tolerance of no more than +/- 10m and that is difficult on a gusty day. It requires full concentration from the whole crew over several hours and if any extraneous member strikes up bored conversation about last night’s game they’ll be told to shut up as we’re all concentrating.

Bodies are even more difficult to find because they’re mostly water and sonar is designed to see straight through water so you need to be over 700Khz to even stand a chance. The ultrasound used to image babies in the womb is around 1100Khz and can see about as far as it needs to in order to image a baby!

So what use did we find for these talents?

While we were still looking for K7 and Donald in 1998 we heard of a diver being lost in Ullswater so we dashed over there and soon had a clear image of him lying on the bottom. It was all recorded on thermal paper in those days. The printer whirred away in a wooden box with a clear acrylic lid so we could watch it go by and now it’s rather faded, but like everything else, the rolls of paper are still carefully stored away in the archive. The Police divers were initially sceptical and at the time their search techniques were exactly the same as used in 67 but here we were with a picture taken from a boat that clearly showed the casualty and, what really sold it, was I was able to describe his kit configuration – single 15 litre bottle on the right, pony cylinder on the left (that’s a small bottle to get you to the surface in the event you have to bale out).

This is probably going to take you a few moments but look at the image above from a distance and soak it up for a minute or two. It won't mean a thing initially.

Then look at the image below.

It's a diver, face down and partially buried in the mud. His arms are either side of his head and he has two cylinders on his back. Head to the right, bottles to the left. Now go back to the top image and keep looking until you see it. That image has never been seen in public until now and neither has this one. It's a scanning sonar image of the same site.

Below is a closeup of the area highlighted in the red box. The diving cylinders are clearly visible, you can even see the straps around them.

Unfortunately, in 98 we were yet to perfect the techniques we would later hone to put a ROV onto a target then get a diver down. We tried but the police divers weren’t able to get onto him due to our undeveloped techniques so we reluctantly had to abandon the effort – for the moment. But we’d started something with the police team that would be a game changer.

Then we found Donald after he’d been lost for 34 years and people really started to take notice.

So in 2002 we resolved to go back to Ullswater and finish what we’d begun and by then we had this down. It was the work of a Sunday morning to image him on the new sonar, home in with a scanning head then get the ROV in for some footage. The other ace we held was our first name terms relationship with the Coroner so it became a case of, we have a body for you. This time we could provide enough accurate surface support so the police team could recover him in a single, swift and safe operation and so we had the bittersweet pleasure of working alongside the Lancashire and Cheshire joint underwater search team to recover Cliff Purdham and return him to his family.

We provided surface support and real time survey, the police team did the heavy lifting

Cliff was brought ashore at the outward bound centre further down the lake privately and away from onlookers before being returned to his family.

But here's a question. Without the explanation of what each sonar image shows would you have worked it out on your own? That's the real black art of acoustic imaging - interpreting the data.

We went on to do a lot of work with the Lancashire and Cheshire unit who went on to become the most proficient underwater search unit in the UK. The shot of the machete going into the Mersey on a rope was one of our more interesting training exercises. No one had done that before.

We worked with the Humberside team too flying a fish upside down to search moored ships for external containers filled with contraband and with the Met team on techniques for under water counter-terrorism ahead of the 2012 Olympics. Our expertise was sought on several high-profile murder cases where water was involved including the Lady in The Lake case in Coniston and others I won't mention here. We shot images for the first series of Deep Wreck Mysteries and solved the 86 year old mystery of whether Titanic's sister was mined or torpedoed by locating the German mine cradles in 130m of water. Our sidescan imagery of the German anchorages where Tirpitz and Scharnhorst lay is second to none.

We were involved in several body recoveries and to this day I am still consulted. I was asked for an opinion on the tragic case of Nicola Bulley and my appraisal turned out to be eerily correct.

I could write a whole book on our underwater adventures and maybe one day I will but for now, Google 'Britannic sidescan' and see whose images come up at the top of the search.

Could any old divers have done what we did? Maybe - but they didn't.

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