Appeared in DIVER September 2006

Missing the wreck

Youre down the line, but where is the promised wreck No sign of it - so what do you do now John Liddiard has all the answers

ITS A DISAPPOINTMENT that most of us have suffered at least once in our wreck-diving careers. The shotline is dropped, divers finish kitting up, the boat manoeuvres in and buddy-pairs enter the water. The excitement builds as the line is followed down, the light slowly fades and dive lights are switched on.
Staring into the gloom, every slight variation in light builds a level of excitement. The seabed comes into view, we get to the shot and - nothing. The wreck is nowhere to be seen.
These days, with differential GPS, high-resolution colour video sounders and very professional and conscientious charterboat skippers, missing the wreck is a pretty rare occurrence. Gone are the days when a scummy fishing boat making a few extra pounds at the weekend would drop the shot somewhere roughly in the vicinity of the wreck and hope for the best.
These days, the skipper will check the shot and either pull it into the wreck or recover it and try again until he is confident of success.
On the rare situations that a shot is not on the wreck, nine times out of 10 it will have pulled loose while the divers were on their way down.
So, knowing that the skipper will do his best to make sure the shot is dropped in the right place, what can we divers do to make sure we actually dive the wreck

At St Paul Island in Nova Scotia, skippers dont keep the boat live. They drop an anchor and turn off the engine before divers enter the water.
On my first dive, I followed the anchor-line down to find rocks and no wreckage. Even in good visibility it took me a good 20 minutes to find the wreck. When I did, I looked up, and there was the silhouette of the boat above me.
The local convention was that the skipper anchors to leave the boat above the wreck, not that the anchor is on the wreck. If only I had just dropped straight down.
It may be an unlikely scenario, but it does show that making an assumption about how things work can lead to the wrong result. If I had asked the skipper, he would no doubt have told me before the dive. If he realised I didnt know what I was doing, he would no doubt have told me anyway.
There are many things to check with the skipper before entering the water. Perhaps the most important in UK conditions is whether it is safe to pull on the shotline, though with current or groundswell, pulling may be hard to avoid. So is the shot tight enough into the wreck to pull down it, or do we have to take care not to pull on it
The skipper may provide advice to follow on reaching the bottom of the shot. Has it been dropped on the wreck, or on the rocks nearby What is the most likely direction
What is the actual depth of the wreck and seabed on the echo-sounder In which direction does the bow point Is it across or along the current
Better to know all this before leaving the boat than to start wondering at the bottom.

hspace=5 When pulling down a shotline, we can usually feel whether it is hooked in or dragging. Sometimes it will start secure, then suddenly ping loose.
If a shot is dragging fast, the best thing to do, dive profile permitting, is to use any slack in the line to hit the seabed fast and take the slack down with you. Dont waste time pulling or swimming along the line, as it will only drag faster. The faster you hit the seabed, the less it will have dragged.
On the seabed the current will be less, and so will the drag on the shot. With the line pulled close to the seabed, the shot will dig in. The line can then be followed upcurrent and the
shot planted.
Even if there isnt enough slack to pull the line down to the seabed, letting go, hitting the seabed, and searching upcurrent may still be a better bet than dragging the shot further.
It all depends on how far away the seabed is, how strong the current is, and how fast the shot is dragging.

If a shot initially caught the wreck, then pulled and dragged, following the furrow or snail trail it leaves in the seabed may lead back to the wreck.
Or it may not. Perhaps the shot missed the wreck completely. Perhaps it only hooked a rock before pulling loose. Perhaps it dragged past the end of the wreck or along the keel.

hspace=5 Whatever means you use to get to the shot, whether pulling along it, swimming down it or hitting the seabed, if it isnt on the wreck and is dragging, top priority is to stop it dragging further.
Plant the shot as firmly as possible under a rock or any dispersed scrap of wreckage or, failing that, just push it hard into the sand or gravel. That way, things wont get worse for any other divers on the way down.
Once planted, a secondary consideration is to take your time and assess whether the shot can be recovered later. But the last divers down should be taking care of this, so unless you are last, this isnt a priority.

When the shot isnt on the wreck, is the best option to go looking for it, or to abort now, stop any other divers on the way down, and give the skipper a chance to shot the wreck again
The first consideration is whether aborting to dive again in 15 minutes time would be safe and practical.
Get much past 30m and aborting and starting again would not be a safe decompression profile. Gas used on the descent and ascent may also mean that there is too little left for a second attempt. Much shallower than 20m, time will not be a serious constraint, so there would be plenty of time to search.
Its the gap between these two cases where I would be very tempted to abort and have another go.
But there are other considerations. Is slack water long enough How long will it take to get back on the boat and ready to dive again A hardboat with a diver lift makes this decision easier.
Finally, aborting to have another go can work only if everyone aborts. If other divers are already off looking for the wreck, it may not be safe for the skipper to pull the shot and drop it again before they have finished.

A wreck that sits on a soft seabed in a current will have a scour about it, particularly at the bow and stern. It may only be a metre or so, or it may be bigger than the wreck.
Some wrecks sit in their own depression below the level of the surrounding seabed!
In low visibility or low light, the shot could have missed the wreck by far enough that I cant see it, but still be close enough that it is in the scour. Simply heading downhill will lead into the scour and hence to the bow or stern of the wreck.
Keeping an eye out to the sides may reveal the wreck earlier.
If it looks like a natural slope rather than a scour, a change of strategy will be required.

On a dive on the Aeolian Sky, the shot caught on a plate near the keel. The way the wreck has collapsed, the hull plates near the keel are almost flat to the seabed and, near the middle of the wreck, have accumulated a few centimetres of silt.
I returned from a great dive to find two pairs of divers who had started after me already back on the boat. They had aborted as the shot was not on the wreck. Yet divers who had started after them reported that the shot was still on the wreck.
On a dark day, the complaining divers had seen only the silt and decided to abort. Had they followed the line to the end, they would have seen the wreck. Had they pushed a finger into the silt, they would have felt it.

Rightt: If you see a hull plate with ribs, more wreckage probably lies the way its pointing.

Leave the air turned on and watch the needle for 10 minutes. If the intermediate pressure creeps up, this is a sign that air is leaking past the first-stage valve seat because it isnt closing properly.
The malady is called first stage creep or IP creep. The first stage needs attention.
If you dont have an IP gauge, the usual symptom of this is a regulator that is perfectly all right while it is being breathed from but, if it is left alone for more than a few breaths, will slowly start to hiss air from the second stage.
The IP has crept up to the point at which it pushes the second stage open.

If we cant see the wreck, we may be able to see its shadow, especially in good vis.
I like to take my time and let my eyes adjust before chasing off after shadows. I note the direction of the shadow and turn a couple of circles looking for others. Only when a convincing shadow appears consistently in the same place would I consider it worth chasing.
But before doing any of this, have another thought about what the wreck looked like on the echo-sounder. Is it big enough to have a shadow
Remember to look up from time to time - you may be swimming under the bow or stern.

Sometimes bits of wreckage will be dispersed from the main body of the wreck. Perhaps the shot is hooked on such a scrap, or maybe we find a scrap while searching.
If we are lucky, there will be hull with ribs showing. The closest ribs run across a ship. Provided the collapse of the wreck was not too catastrophic, the ribs may point towards (or away from) the wreck.
With a recognisable bit of wreckage, knowing where it should have been on the ship can be a pretty good clue as to where to search, especially if you have just refreshed your memory by reading the Wreck Tour!

Shoals of fish like this pouting often collect off the ends of a wreck. Even when no shadows are evident, a shoal of fish may indicate the direction in which to look.
There are two initial possibilities: the fish are between you and the wreck, or you are between the fish and the wreck. So having seen a big shoal moving consistently in one direction, first look round and make sure that the wreck is not behind you!
As we move towards the shoal of fish, they will move away. Just following the fish will lead in circles. So having chosen a direction, we need to stick to it without letting the fish distract us.

It may surprise you that I have left traditional reel and line search methods to last.
This is the most thorough way of searching an area, but it does take time. On a deep dive with limited bottom time, using all the evidence to provide a good guess may be considerably faster. Or it may miss the wreck completely.
A line can be laid to make a circular search, or to swim out and back on a cross or compass-star search. It may produce a fast result, or you could turn the wrong way and spend 15 minutes following a circle the long way round before finding the wreck.
Some consideration needs to be given as to where to attach the search line. If the shot could drag or may be pulled before the divers return, attaching the line to the shot is not a good idea. On the other hand, if the dive plan requires returning to and ascending the shot, attaching the search line to it is essential.
Our other tricks can provide clues as to the direction in which to start searching.
My preference is to go a metre or two upcurrent to begin. If I was to start a circular search this way, at some point it would foul against the shotline. But that doesnt matter, because I prefer to use an out and back cross or star search.
That way the line never fouls and I dont need to keep any tension in the line, so I can just plant the clip on the end in the silt or under a small stone. If I find the wreck, I can leave it for others to follow or pull it loose and wind in.

Does the wreck lie along or across the current Wrecks lying across the current are usually the easiest to shot, and easiest to find if the shot has missed. Lacking any other evidence, searching into the current is usually a good bet.
If that fails, looping back to one side before searching downcurrent covers the possibility that the shot has caught upcurrent of the wreck. Unless, of course, we are looking for a wreck in Nova Scotia!
If a wreck lies with the current, there is a good chance that the shot lies alongside the wreck. The search has to include working across the current. As to which way to try first, maybe some of the other tricks provide a clue.

Deep in my pocket I carry a waterproof hand sonar, officially good to 45m depth, but often pushed further. It works best with a big intact wreck on a flat silty seabed. I just hold it out horizontally and make a circle. On a flattened wreck among big rocks, it is next to useless.
Twenty years ago I used it on one dive in five. It paid for itself in just a few missed wrecks. These days it is used less than once a season. So rarely, in fact, that last time I wanted to use it, the clip was jammed and I missed the wreck!