One of the hardest skills for some divers as their diving career progresses is learning to use a compass. Once you’ve mastered the technical aspects of making sure it’s moving freely and not locked off inside the casing, the biggest hurdle is trust. You need to gain a Jedi like perspective as you accept Obi-Wan’s guidance to “Use the Force”. And generally, that’s fine, until there’s a nearby wreck and your compass stops being attracted to the earth’s magnetic field and starts interacting with the ship’s magnetic field instead.
When iron hulled ships were introduced, the effect of the metal hull on steering compasses was first observed. During construction the metal in the ship adopts the magnetic field of the dockyard used for construction. In modern construction methods, the high currents used for welding the steel plates together create magnetic dipoles in the steel, thus magnetising the ship…
During the American Civil War, mines were developed that were activated by contact. The target ship hits the horn on the mine. The soft metal of the horn buckled under impact, smashing a glass ampoule with battery acid inside. The acid electrolyte dropped into the waiting battery, energizing it and heating a platinum wire inside the mercury fulminate detonator. Boom.
At the start of WW2, the Germans developed a new magnetic trigger for mines. For a while the British were stumped as to how these mines worked. But in November 1939 a German mine was dropped from an aircraft and landed on mudflats in the Thames estuary at low tide. The mine was disarmed and taken to Portsmouth, where the mechanism was examined. A magnetic needle which was pulled by the target ship’s magnetic field completed the circuit and fired the mine. Later sophisticated versions would use a counter that didn’t fire for the first few ships to pass.
Establishing how the mine worked held the secret to protecting vessels, you just need to wipe out the magnetic signal. Magnetic field strength is measured in units named after Carl Guass, so the process of removing the magnetic signature is known as degaussing. Remove the magnetic field from the ship and it can safely pass over the mines without triggering an explosion.
There were two ways of cancelling out the ship’s magnetic field. The permanent one was to put thick bands of electrical wire around the length of the vessel, known as coiling. Passing an electrical current through these cables generated an electromagnetic field that cancelled out the ship’s own field, thus rendering the ship invisible to the mine mechanism. Royal Navy Commander Charles Goodeve oversaw this system, and it even allowed for the polarity to be reversed when ships were in the southern hemisphere so that the ship appeared to have the same magnetic field as the natural background. But this equipment was expensive and difficult to install.
Measuring a ships natural magnetic field was a complex business. A series of magnetometers are anchored to the seabed about 5 metres apart for a 150 metre run. Each magnetometer wa connected to a fluxmeter on the shore. The ship passed over the magnetometers and the readings from the fluxmeter were used to create the ship’s signature. From this starting point the number of turns of the degaussing cable could be increased or decreased, or the current altered until the signature was minimised.
A second quicker method was to wipe the hull of the ship, with a current carrying cable running a pulse at about 2000 amps. The large cable was dragged down the sides of the ship in a process known as deperming. This wasn’t a permanent solution though, as the ship travelled through the Earth’s magnetic field it slowly became magnetised again. This started in late 1939 and helped protect many of the vessels that carried out the evacuation from Dunkirk. In a 4 day marathon session prior to the evacuation over 400 ships were ‘wiped’ in this way, though there are concerns that some of the ‘wiping’ may have not been as effective as hoped. The Isle of Man vessel Mona’s Queen was lost to a magnetic mine on 29th May 1940 just outside Dunkirk harbour, and stories persist to this day among the relatives of the crew that the ship wasn’t properly protected.
Any diver who has been to Scapa Flow to visit the remains of the World War I German naval fleet will know the story of the 21st June 1919 when 74 ships were scuttled. Due to some heroic efforts only 52 ships actually hit the seabed. Initially, the British Admiralty were determined to leave the German fleet on the seabed and let them rust. But the wrecks were a considerable hazard to local vessels, with several being grounded on up-turned hulls. By 1922 the demand for scrap metal had increased and the Admiralty started selling off the wrecks for salvage, £250 for a destroyer and a mere £1000 for a whole battleship (of course 100 years ago that was the equivalent of £54,000 but that still seems cheap).
Over the next 8 years Ernest Cox developed some incredible techniques to lift huge battleships from the seabed within Scapa Flow. The wrecks were salvaged for fixtures and fittings with artefacts being recovered in good condition including bottles of wine, musical instruments, and the metal ships were broken up for scrap sales. By 1930, the price of scrap metal had crashed leaving the whole operation in danger of financial ruin and by 1933 Cox sold out to Metal Industries Group and they lifted the last of the battleships in 1939 as World War II loomed. Just 3 battleships and 4 cruisers remained. These are the wrecks that divers now visit, but they all bear the scars of the salvage work carried out by Nundy Ltd and then from 1970 by Dougall Campbell as Scapa Flow Salvage Company. Explosives were used to blow holes into engine rooms to get the non-ferrous metals and to open up the hulls to recover the valuable torpedo tubes. Campbell also realised that the armour belts of 14 inch thick steel with a high content of nickel and chrome were easy to recover and valuable enough to be worth the effort. [Dougall freely shared his amazing knowledge to a number of Scapa Flow projects in advance of the centenary, and sadly passed away on July 26th 2018].
Sensibilities have changed regarding wrecks and their salvage. HMS Vanguard is now considered a war grave after she was lost with 845 men following an explosion in her magazine in July 1917, but by the 1950s and then again in 1970s, she was salvaged for her propellers, condensers, torpedo tubes, armour plating and Weir pumps. It wasn’t until 2002 that the wreck became a Controlled Site and diving was restricted, but for 85 years she was stripped of any useful metals ie the ones that would command a good price on the scrap market.
Early salvage operations were driven by the demand for scrap metal. In post WWI industrial development was being held back by lack of metal. But post WWII there was a new driver for recovering steel produced before WWI, lack of background radiation in the metal itself. As the nuclear and space races took hold on the 1950s and medical advancements in 1960s, there was a growing demand for steel that had very low levels of background radiation. Atomic testing in the 1950s released Cobalt-60 into the atmosphere. Steel production involves pumping air (or oxygen) through molten pig iron, which reacts with impurities creating oxides that can be removed as slag. Atmospheric atomic tests released atmospheric radiation which peaked in 1963, so any air or oxygen used to produce steel since that time introduced low levels of background radiation into the metal.
Ordinarily, this isn’t an issue. You wouldn’t notice or be affected by a trace in your cutlery or the spice rack in your kitchen or the panels in your car. But it matters if you are trying to build sensitive instruments to detect radiation. Geiger counters, body scanners and space equipment can all be affected by the low level of radiation introduced during the manufacturing process. That makes the steel armour plating from the pre-atomic era significantly more valuable than would otherwise be the case. Our latter found sensibilities to protect the wrecks as war graves wasn’t apparent decades ago. In Scapa Flow the salvage has stopped, but internationally wrecks are disappearing in their entirety. Happily, the half-life of Co-60 is short, only 5.26 years. Since the moratorium on atmospheric testing in 1963, levels of atmospheric radiation have been rapidly dropping, with only occasional contributions from Chernobyl, Windscale, Three Mile Island. This means that production of low background radiation steel is now possible, combined with computerised correction for background levels. However a drop in the market value of pre-atomic steel is unlikely to save wrecks around the world, particularly in Asia where even the former pride of the British Navy HMS Prince of Wales and HMS Repulse have been targeted by metal scavengers.
July 1969 is best remembered in popular culture for the Apollo 11 moon landings and Neil Armstrong’s declaration of “..a giant leap for mankind.” But at the same moments as the world was transfixed by NASA’s reports, another equally challenging expedition was underway off the North American coastline. Six men on board the Ben Franklin drifted for 30 days in the currents of the Gulf Stream, using very little power apart from their floodlights.
The Gulf Stream project grew out of earlier bathyscaph explorations. Bathys means deep and skaphe means light boat. Bathyscaph expeditions were designed to explore the depths, to plummet to the sea bed, make observations and then return to the surface. During the 1950s successful dives were made into the Marianas Trench at a depth of over 10,000 metres.
The Ben Franklin was different, she was a mesoscaph, meso meaning middle, and her design reflected that idea. The Ben Franklin was designed to be a light vessel using modern steel and Plexiglas to ensure that in the event of any problem, she could always return to the surface. Whereas launching bathyscaph required considerable winch power and large support vessels, mesoscaphs were expected to operate in shallower waters, with minimal surface support.
It took Jacques Piccard, a Swiss oceanologist (and no relation to Jean-Luc) nearly a decade to design and build the Ben Franklin. Jacques father, Dr Auguste Piccard was himself an ocean explorer who designed bathyscaphs and it was his discussions with Jacques that initiated the mesoscaph project. The design was a cylindrical cabin capable of holding the crew, with 400kg of Lithium hydroxide in panels to absorb the carbon dioxide, over 1100 kg of silica gel to absorb the water and reduce humidity, 250 kg of liquid oxygen and enough dehydrated food to last for 30 days. Piccard orginally envisaged the interior being lined with mahogany, to emulate a fine yacht, but was overridden and the internal structure was clinical and white.
Setting out from Florida, there was no big fanfare or press launch. The initial plan was to see if they could last 3 days and then make a decision over whether to continue. So on 14th July 1969 the Ben Franklin was towed into position and at 20.34 the hatch was closed. The crew descended initially to the bottom of the sea and then rose slightly controlling their descent by ditching ballast weight or adding air to ballast tanks. Over the next 30 days they would drift for 2800 km at speeds between 0.2 and 3 knots. They experienced internal waves within the Gulf Stream that would cause their depth to oscillate by over 100 metres, although the rate of rise didn’t concern the crew. They established that there was perceptible daylight at 600 metres and conducted a series of acoustic measurements using explosions set off from two surface support vessels.
On board for the trip was an observer from NASA, whose primary function was to look at the interaction between the crew. 50 years ago NASA was already considering the International Space Station and longer voyages to Mars. The Gulf Stream project provided an ideal test bed to study sleep patterns which deteriorated after the first 3 weeks and eating arrangements, as crew members chose to eat alone rather than together. Bacterial contamination, firstly of the cold water supply and then of the walls and floors would have posed a serious threat to the crew had the experiment continued beyond 30 days. Even an increase in the cleaning regime failed to stem the growth of bacteria.
Communications between the Ben Franklin and the surface support vessel the Privateer take place using an acoustic telephone, and the recordings made by the NASA observer show that the stress levels of the crew rose enormously at times when communications were restricted by weather or surface vessels deviating their course due to other ships. On 24th July 1969 as the crew of Apollo 11 splashdown into the ocean, the crew of the Ben Franklin are experiencing a temperature of 14 degrees and tumultuous seas as the internal waves catch the vessel. It wasn’t until 14th August that they surfaced and at 8.09 the hatch was opened. They were due east of Baltimore and the US Coastguard vessel Cook Inlet was there to rendezvous with them. A week later the Ben Franklin had been towed into New York for a hero’s welcome. A remarkable tale of human endeavour had come to an end, but in a world transfixed by the moon it was barely noticed.
Michelle has been scuba diving for nearly 30 years. Drawing on her science background she tackles some bits of marine science. and sometimes has a sideways glance at the people and events that she encounters in the diving world.