Differential GPS is an absolute must for a variety of reasons, but first a brief explanation of what it is. GPS, in its standard form, relies purely on satellite information and due to various atmospheric phenomena and the deliberate degradation of the signals, it is not especially accurate. In order to get around this problem, there exist shore beacons to transmit correctional data. These shore beacons are at precisely known locations and of course, they never move. They receive exactly the same satellite data as your boat and compare the position calculated from this data against the actual position which is, as I said, precisely known. This shore based beacon then sends a data string that can be interpreted by a separate receiver on the boat and interfaced to the existing GPS in most cases. What this means is that your accuracy when placing the boat over a wreck just went from 30m to about 5m on a bad day. Clever eh? You will need a separate receiver and an extra antenna on your boat. Your existing GPS may have DGPS capability but it won't work without the necessary signal.
What this really means is that you can forget about using shore transits forever. When the machine says that you've arrived, the wreck will be on the sounder screen.
Have you ever gone to where you absolutely know that there's a target because you've been there before, but for some reason it just refuses to show itself? The only thing worse is going to a target that might not be there at all and looking at the same blank screen not knowing whether you've just missed your wreck by next to nothing. What about those wrecks that are definitely out there somewhere but your information simply isn't accurate enough to get you there? This is where the magnetometer comes into its own. In essence the magnetometer is simply an extremely sensitive metal detector. It is deployed by towing a 'fish' behind the boat. Within this fish is a cylinder filled with kerosene or similar hydrocarbon liquid, and around the cylinder is a coil. When the coil is energised the molecules in the liquid align themselves along the lines of magnetism from the coil, and there they stay for a short while until the earth's own magnetic field slowly disrupts them. Place a few thousand tons of scrap iron on the seabed and what you get is a major disruption of the earth's magnetic field in a localised area and it is this disruption that the magnetometer sees. What this means to us wreck hunters is that we can detect a wreck and know that it's down there, long before we actually see it on the sounder.
Using DGPS, even without a magnetometer, transforms a wreck hunt. In the last article it was explained that upon reaching the possible wreck site the GPS should be ignored due to it's inherent inaccuracy, and a large marker buoy should be used to provide a visual reference while the area was saturated in sounder coverage. Well forget all that as soon as you get your DGPS receiver wired up. With DGPS the position will stay put and allow you to conduct your search straight off the plotter screen. Even a hand held GPS has a plotter screen these days and it allows the operator to see not only where the boat is in relation to the original target position, but also, where it's been by drawing a trail behind the boat's position. Once again, take the instruction book to bed with you and learn how to use the plotter. Having arrived at the target position, you can run a set of parallel lines up and down the screen until you are sure that you've covered the required area. It takes a bit of doing, to draw straight lines on the plotter screen with the wind and tide doing its best to shove you off course but unlike the old marker buoy method, if you miss a bit of seabed, you can see it on the screen so you can go back there and fill in the gaps.
Another advantage of conducting your search straight off the screen is that you won't draw as much attention to yourself as you would with a huge marker bobbing about. And I absolutely guarantee that the first time you're diving that new secret target that you spent weeks looking for some aggravating boat full of nuggets pulls alongside and says 'oh we haven't dived this one before'. You'll feel like painting your RIB battleship grey and only coming out at night!
Just a couple of extra advantages of using DGPS that are worth considering. Up until now, unless your shore transits are especially good, the shot will just go where it goes and on a big wreck you could end up anywhere. Using DGPS, not only can you put the shot into the same place every time, but you can have a separate position for the bow, stern and boilers for example. Visiting divers will look at you with open admiration when you ask them which part of the wreck they would like to dive on. Of course, by doing this, you will quickly learn your way around the wreck which means that it's sooner rather than later when you suddenly start to see the goodies that you've swam past ten times! And it goes without saying that if you know the wreck, you're less likely to find yourself lost. Consider this also, many of the wrecks around our coasts are either mine or torpedo victims, and either way there is a colossal bang, the ship gets a big chunk blown out of it and the rest lands in a heap nearby. If it's a mine, especially a contact mine, the bow section may well be shattered and lying some distance from the wreck. Likewise, torpedoes tend to break a ship in the middle and all sorts of wreckage flies off in the explosion. One day you'll be approaching your wreck on your DGPS and there will appear on the sounder a piece of wreckage that is quite clearly well off the main wreck. Until the navigation became precise you would have just assumed that this was a piece of the main wreck. Kit up and get over the side!
If you now combine these advantages with a decent magnetometer, you can have some serious fun. It's not vital to have DGPS capability to use a magnetometer, some of the search techniques described in the previous article can be applied but it is certainly an advantage.
What I would seriously recommend to anyone who hasn't used a magnetometer is to take the thing out and do some serious practice. Magnetometers are strange animals and it is only with practice that you will learn what is real and what is spurious. On the magnetometers that we will find ourselves using, the display is either in the form of a meter with a needle that is deflected left or right, or an LCD screen with a graph, the deflection being above or below a horizontal line. The magnetometer must be tuned for its geographical location and then, when in use, it will just show a flat line like a disconnected heart monitor, or a needle that doesn't move. Every two or three seconds, it will pulse to energise the 'tow fish' but apart from this it will do nothing until you take it near a wreck.
Go to a known wreck site and, as I said, practice. Pull the fish close to the wreck, over the wreck, round in circles, pull it past at a distance. Try it on small wrecks and large wrecks. Each of these will produce a different result and help you to get a feel for the machine. Iron ore deposits, submarine cables, any old pieces of junk, all will play havoc with your magnetometer until you learn what you can disregard and what is real, so practice.
When you think you've got it and it's time to go in search of something new, the same techniques apply only the magnetometer will speed things along dramatically.
Have your GPS or DGPS take you to where you think the wreck should be, either put the marker in the water or go to your plotter screen. Take the boat quarter of a mile North and deploy the magnetometer fish. Slowly head back towards your starting position and travel quarter of a mile South of it. Just suppose that as you passed to the South of the position, the magnetometer gave a flicker. Bear this in mind and run a similar line from East to West. Now supposing that there is a similar flicker to the West of the start position, this places your target somewhere to the Southwest of the original position and allows the search to be conducted in that area, clearly saving a great deal of effort. This doesn't always work but it's worth doing a quick search in this way just in case the wreck is very close to its given position.
If this doesn't turn up your target things get a bit more involved, you will need to decide how large an area you want to search and how close you will need to get for the magnetometer to detect your target. This is related to depth of water and the mass of iron you're looking for, you will need to plan a search, either a set of parallel lines or a circular search working out from the start position. Either way, if there's a lump of iron down there, the magnetometer will not miss it and it'll see it long before you do!

By Bill Smith.

TROUBLED WATERS
Belfast is a city with a seafaring history as rich as those of Liverpool, Glasgow or New York, but whose reputation over the latter part of this century has all too often been a dark and violent one. The city began to thrive towards the end of the 18th century with the introduction of machine spinning and weaving. Ships loaded with cotton from America's southeastern seaboard would queue to take up the available space on the many wharves. The city became famous for its linen and the tobacco industry was an additional link with America. At one time Belfast had the world's largest rope works, busy supplying the sailing fleets of the great nations

The superstructure of the ferry 'Norse Viking' started to vibrate gently as below the engines and thrusters of the huge ship began to drive her into reverse and alongside the berth. Ahead the huge yellow gantries of Harland & Wolff broke up the granite grey morning sky. As we pulled gently up to the quayside conversation turned to ship building, the Queens Island yard and the slipways that had given birth to the maritime legends Titanic, Olympic and Britannic.
This century it was the heavy industries of ship and aircraft building that made Belfast famous. At the outbreak of the Second World War the port, with its large graving and floating docks, became a naval base and later an Admiralty dockyard. During the Battle of the Atlantic many of the offensive operations directed against German U-boats were controlled from the Belfast. Belfast was also one of the chief connecting links between Great Britain and the United States, with huge quantities of foodstuffs, munitions and military supplies of all kinds being landed there. Out in the Lough enormous convoys of merchantmen and escorts assembled for the Atlantic crossing and for operations in the Mediterranean and North West Europe. The Germans made the city a high priority bombing target and in five air-raids during the spring of 1941, all quarters of the city suffered severe damage.
The clatter of ferry workers unchaining the HGV's from the deck signalled that it was time to disembark and in no time we were motoring out of the terminal. Sweeping along with the morning rush hour traffic we passed by shipyards that had helped to build over a million tons of shipping to aid in the 'tonnage war' and the Shorts Aircraft factory whose flying boats had proved to be a significant factor in the defeat of the U-boats.
A brief journey down the southeastern side of the lough and we arrived in the bustling seaside town of Bangor, Co.Down. At the lifeboat station car park we met Tony Vincent of D.V.Diving who were to be our hosts for the long weekend. As the divers assembled their kit we discussed the plan for the day. The first dive was to be the 'CHIRRIPO' an Elders & Fyffes cargo liner of some 4050 tons that had been torpedoed by the UC 75 on the 28th December 1917 whilst on a voyage from Liverpool to Kingston Jamaica with a general cargo.
With all the equipment loaded aboard the 6.5m RIB we left the relative safety of the harbour and began the twenty minute run to the site of the Chirripo. A building easterly wind and short choppy swell made for an 'interesting' ride northwesterly across the lough to below the imposing cliffs of Black Head. Half a mile southeast of the cliffs and lighthouse on Black head, Tony soon picked up the small buoy D.V. Diving have secured to the stern of the Chippiro. The dive boat had arrived bang on slack, so within minutes of tying the painter into the shot seven divers began the brief descent to the wreck.
The wreck lies on its starboard side, the shot crossing over the port gunwale at around 18m. The first things to greet you are the huge mooring bollards that stick out at right angles, their ropes still wound in a figure of eight around them. Facing the wreck and dropping down across the deck, the remains of the accommodation section can be seen off to the left, the girders and spars all thickly covered in orange and white plumose anemones. Halfway across the deck are the remains of a hold winch and just forward of this you can swim forward into the hold. The seabed at 32m is soft sand with broken shell and all the lower sections of the wreck are covered in a fine layer of silt. Swimming forward along the seabed you pass large amounts of jumbled wreckage and debris that has fallen off the ship as she sank. The end of the debris field is marked by the huge links of chain from the starboard anchor, coiled into a concreted city that is the home to the inevitable squat lobsters.
It is possible to enter the forecastle and swim up inside the bow, your lights glaring back at you from the abundant dead men's fingers and cauliflower sized anemones that have grown on the cross-bracing. Above the brighter shallower water guides you to the port gunwale and once out of the forecastle it is an easy swim along the gunwale and rails back to the shotline. Using air for the dive, the computers showed just a one minute stop for forty minutes of bottom time.
The journey back to Bangor took a little longer than the outward run. Tony needed to dodge the RIB skilfully through the peaks and troughs of waves that had continued to build while we had been down. Crossing the lough the RIB passed several types of ferries and freighters, testament to the fact that Belfast is still one of the busiest ports in the UK. With the RIB safely moored up, it was time for a look around the town and harbour. Bangor has all the facilities that you would expect from a seaside town. Along the promenade hotels, guesthouses and B&B's compete for space with cafe bars, restaurants and pubs. The harbour has both a commercial quayside and marina which was crowded with expensive yachts and cruisers. One surprising feature was the number of palm trees that have been planted around the marina walkways, they certainly giving the place a distinct riviera feeling.
Looking across the lough from the lifeboat station, it was obvious that we weren't going to get far offshore that afternoon. The horizon was 'simmering' and even the big fishing boats had put in to Bangor as winds from the tail end of hurricane David were beginning to build from the southeast. Back aboard the RIB, Tony decided that the best plan would be to keep inshore and dive a wreck called the ANNAGHER in about 13m. Although we had come equipped to do some of the sub 30m wrecks and it could probably be argued that four divers using twin 12 litre bottles and one with a 15 litre and 3 litre pony may be over-kill for a wreck in 13m. Despite this the tragic history of the Annagher made her an interesting prospect.
On 11 December 1937, the 586 ton Kelly Line steamer Annagher had sailed from Belfast for Llanelli, her two hatches filled with a cargo of scrap metal. As she rounded Grey Point the crew noticed a slight list to starboard. With a following wind, the Captain, James McCalmont, decided that it would be too dangerous to head out into the Irish Sea. As the Annagher began to turn back for Belfast the full force of the wind hit her broadside on and caused the ship to heel further over to the point where her cargo shifted and she started a 'death roll'. Captain McCalmont began to run for the shore at Ballymacormick point, the crew were up on the decks over which waves were starting to break. Sounding her siren and firing distress rockets the ship tried desperately to make the beach but as the lifeboat crews assembled the steamer gave a final lurch and went down. Of her crew of ten only one, the mate William Hunter (a non-swimmer!) survived. The bodies of the other nine were washed ashore over the next few tides. A number of attempts were made to salvage the ship but when they failed she was dispersed using explosives.
Due to the efforts of the salvage and demolition teams, the site of the Annagher is now wreckage rather than a wreck although large chunks, most noticeably her boiler, are dotted around the site. The vis on the wreck was only a few metres but this actually added to the intrigue of trying to identify parts of the wreck as opposed to parts of the scrap cargo she was carrying. The disarray of tangled wreckage has an abundance of nooks and crannies and the wreck has become home to major colonies of marine life. Crabs (swimming and edible) and Lobsters (common and squat) make use of all available holes in the metallic mound. The shallow dive made for a pleasant way to round off the first day.
At breakfast the next morning, we watched as a trawler steamed into Bangor, the wake it created being the only disturbance on the flat calm sea. The plan was an extended range dive on the former Anchor Line ship TIBERIA, a liner of some 4880 tons and 404 feet long. Being a big target the aim was to line off the shot in different directions and explore the upper decks in 55m. This way we felt that we could pool our information and get a good idea of her condition.
The ride out to Black Head took no time and soon Tony had the wreck on the sounder, the large black mass of pixels jumping up from a bottom line of 62m. The tides can run quite badly around the northern edge of the lough, and the strong run on the shot meant that we would need to wait for slack. As the RIB gently rolled, Tony told us that we needed to take care around the bow section as it was well netted. The nets came from an incident that had happened on the Tiberia about two years earlier. A small fishing boat, the Golden Isles, had been scallop dredging near the Tiberia when it suddenly snagged its nets. The skipper tried to bring the nets in but unfortunately they were wrapped around the Tiberia's bow and began to pull the fishing vessel under. Frantically the skipper attempted to cut the boat free but the winch, which was jammed open, continued to take the vessel down and he was forced take to the life-raft as his fishing boat sank beneath him.
The tide had stopped running past the line indicating that slack water had arrived. The shotline dropped away through clear green water and it was only at about 45m that you needed to switch your lights on. A quick check on the gauges showed 50m, the wreck should be appearing soon, 55m came up, then below the lights picked out the red of brittle stars - seabed at 60m. Following the shot the lights revealed a strange shape, a sort of metal door lying on its side. Then the torches picked out vivid blue and white colours - a ship's hull.
The shot is in the fishing boat, a line reel is tied off on the bottom of the shot and you can swim off to explore the little ship. The door like object is one of the otter boards used to keep the nets open when trawling so it is best to head away from this as it would inevitably lead to the nets.
The semi covered wheelhouse is filled with jumbled debris that was hard to make any sense of. Ahead the familiar shape of a ship's radio-phone and below it the instrument panel were easily recognised. Compass and throttle levers sit proud of the instrument panel, all covered in a fine layer of silt. Leaving the wheel house on the port side, lights scanned around to see if the huge hull of the Tiberia was close by, but on this occasion the lights only fell away into the darkness and as the run time approached the planned twenty five minutes, it was time to follow the line back to the shot. Using air as a bottom mix and EANx 80 as the deco gas, the deco stops are not too long (on our plan we used air & EANx 60 tables, the extra 20% was a safety factor) the Commander computers soon cleared, long before the 44 mins total ascent time the tables called for.
Heading back into Bangor the RIB passed more fishing vessels that had decided to come in from the approaching Southerly gales, but before we were finished for the day there was still time to ride out to the North-East corner of the Lough and one more wreck.
The small Dutch motor cruiser FREDANJA (277 tons) had been one of the flotilla of small craft that had gone to the aid of the British Expeditionary Force when it needed to be evacuated from the beaches of Dunkirk during Operation Dynamo. Having dodged the shells and Stuka dive bombers that accounted for over forty British ships, the Fredanja had gone back to more sedate coastal work, when on New Years Day 1942 she struck Copeland Island. She now lies upside down on a shingle seabed, her hull broken in two major sections. Swimming down the permanent shot brings you onto the aft section of wreckage. Her rudder is bent out at nearly ninety degrees to the hull, evidence of the force with which she hit the Copelands. Dropping to the seabed in 18m you can swim down the left (starboard side - remember she's upside down) of the wreck to a large hole in her hull. Carefully penetrating the hull you swim into the remains of the engine room where the solitary boiler sits, there's no need to lay a line as the swim through past the boiler is obvious. At one point the debris rises to near the hull and this is a bit of a squeeze through - especially wearing a twin set!
The wreck is split just ahead of the engine room and soon you're back in open water. Forward of the engines comes a widely scattered debris field of small plate and twisted girders. Following the field brings you to the bow section which rises up out of a scour in the shingle. Once again it is possible to enter this section through holes on either side of the hull. The wreck is home to several large conger, one of which has made its lair as far forward as you can get inside the hull before the debris and bow plates meet. As you follow the wreck back down the port side, you pass the remains of a mast and rigging. Several large edible crabs have burrowed under the mast and others live inside the hollow structure. The Fredanja may not be a big wreck but she is still very interesting and the visibility is generally good at about 8m. Two days and we'd already dived four very different wrecks.
As the RIB was hauled out of the marina and onto its trailer, the sun continued to shine and there was little in the way of wind. Perhaps the Met Office had made a mistake in calculating the track of the low pressure and we thought, just maybe, we could get back out into the Lough again tomorrow. You can guess what comes next can't you?
The following morning the sea was speckled and streaked with white horses. Larger ships had come in to ride out the gales and slowly moved around their anchor, an indication of the wind's cyclonic nature. In spite of this we did get a dive in the Lough - but this was the sheltered waters of Strangford Lough. A short drive down the East coast of Northern Ireland and you are on the Ards peninsula that separates Strangford Lough from the Irish Sea. At the southern end of the Lough is the small market town of Portaferry where a small car ferry makes the half mile crossing to Strangford. As the Lough narrows there is some of the best scenic and drift diving in the UK. Tides rip through the narrows and with sloping walls dropping down to 60m, this is an area that demands local knowledge before attempting to dive. That said, the visibility and marine life at a depth of 35m needs to be seen to be believed. Even while you kit up you know you're in for a treat as wild sea trout jump near the boat signalling the marine life activity below. At 15m you can see the sponges and rocky bottom at 25m. Drifting over the bottom you start to swim down to the 35m level, this is about as deep as you need to go. You feel the current begin to pick up and soon you are drifting by at 3-4 knots.
The rock face abounds with marine life. Large Wrasse dart in and out of the protection their rocky lairs offer. Pollack, Sea Trout and Bass flit past as they chase after smaller prey. You lose count of the large Edible Crabs that are seen wedged in the rocks, waiting for the current to drop. Lobsters scuttle backwards into their holes, torch beams illuminating their bright blue shells. As you feel the current beginning to slow down you start to swim up into shallower water for the remainder of the drift. In the shallower water are huge boulders and kelp forests amid patches of sandy seabed. Attached to many of the boulders are the largest sponges I've ever seen in UK waters. Huge, grey 'Elephants Hide' and vivid yellow 'boring Sponges' were everywhere. At the base of one boulder a small octopus sat funnelling water, its colour immediately changed to the white of fear so we backed off so as not to frighten it, though it still shot off into deeper water. The vis in the shallows is normally a couple of metres down on the deeper sections but still, 6-8m isn't bad.
As we surfaced the southerly gale was blowing with full strength, however this only created short 'wavelets' in the sheltered Lough and the RIB soon had us back at the Portaferry launch site. We could probably have had a second dive, but with tide and time pressing it seemed more sensible to have a few jars of the black stuff before catching the ferry back to Liverpool.
Belfast and Strangford Loughs must have some of the best diving sites around the UK and the fact is that there are numerous new wrecks being turned up each year. With the improving political climate and hopes that Northern Ireland can finally begin to move on from the so called 'troubles', this is undoubtedly a place that is going to get more popular with divers in the future - it's certainly fixed on our calendar for another trip.

By Ron Mahoney.