The main object of a floating dock is to raise ships out of the water to enable inspection, painting and repair to be undertaken of their underwater parts. The modern floating dock is evolved from the method first devised by an English captain in Cronstadt harbour during the reign of Peter the Great. This man gutted an old hulk, fitted a watertight gate at its stern, berthed his ship in the hollow shell, closed the gate and pumped out the water. It was not until 1785 that a timber dock was built specially for the purpose by Christopher Watson at Rotherhithe.
The floating dock has hollow walls and bottom, and the most common type is the double-sided dock such as Cox bought. As the floating dock itself needs to be lifted out of water for periodical maintenance and is generally too wide to enter a fixed dry dock, it is usually so designed that it can lift every part of itself in turn out of the water.
The main functions of the dock walls are to provide stability when there is no ship on it, to contain the lifting machinery, to form platforms from which to berth the ship and to provide longitudinal strength. The horizontal portion, or pontoon, of the dock is the platform on which the ship rests, and it provides the buoyancy which raises the ship from the water. The pontoon is subdivided by watertight bulkheads to ensure stability. and the walls are also divided.
The basic principle upon which the floating dock works is that for every ton of weight removed from it, the dock itself exerts an upward pressure of an equivalent amount. Centrifugal pumps are therefore installed as low down as possible in the pontoon and worked by prime movers on top of the walls. As the pumps throw out water, so the ship gradually rises.
As yet Cox had not fully assessed the problem of raising these ships which must inevitably have suffered considerable damage by the pressure of water and years of submersion. To some extent his problem was simplified by their reduction to scrap when raised. The essence of his plan was to utilise the buoyancy of his dock and the lift of the tide to raise the sunken vessels clear of the bottom.
The work was not commenced, of course, without at least a rough estimate of the value of the scrap that would result from the operations. Calculations could be based upon the known general structural arrangements of warships, even though drawings and plans of the German ships had not at that time been obtained by Cox. It was known, for example, that many fixtures and fittings and minor portions of the hull were made of aluminium alloy or other light materials, and high-tensile steels were in general use for important parts. Cast steel was used for the stern, stern frame, rudder frame, hawspipes etc, wrought iron for cables, davits and similar fittings, and naval brass, gunmetal or phosphor bronze for many internal fittings. Cox claimed that he could distinguish with his eyes shut all kinds of metal by merely listening to someone tapping it.
The cruiser had two distinct bottoms; the outer bottom forming the outside of the hull transmitted water pressure to the general structure, while the function of the inner one, which was also watertight, was to save the ship should the outer bottom become unserviceable. The outer bottom was one inch thick near the keels and behind the outer protective plating at the sides, and rather less on the bilge. The inner bottom was thinner. The space between the two could be utilised for the stowage of oil fuel and reserve feed water. Systems of frames connected the two bottoms, certain of them being made watertight in order to subdivide the bottom into a number of cells useful for stowage purposes and also limit the inflow of the sea should the outer bottom be damaged. The upper deck was steel plating supported by transverse beams and longitudinal girders. Watertight compartments were provided by watertight bulkheads and decks.
In principle, battleships and battlecruisers were built in the same way, though the plating was thicker and the scantlings heavier. Bulkheads supported the several decks down to the inner bottom where water pressure transmitted through the framing balanced the loads. In the cruisers, armour formed part of the structure, but in the battleships and battlecruisers it consisted of separate hard plates bolted to the sides of the ship.
The destroyer had no double bottom, and the important framing was more closely spaced, the lower part being adapted to support boilers and engines because of the disproportionate weight of machinery these ships carried. The longitudinal frames stiffened the thin plating of special quality steel which in places amidships was as thin as 0.17 inches.
Cox could learn from naval architects about the structure of warships – he had already broken up two battleships – and so form some idea of the difficulties he might encounter. For example, in all classes of warships, damage below the waterline could at best make a ship inoperable were it not for an efficient system of watertight subdivision. Fairly minute subdivision, too, is necessary to minimise danger from shell fragments or accidents which might perforate the hull. By such means, and by making every deck and flat watertight, ships like Seydlitz and von der Tann had been able to keep on fighting though holed in several places. Even so, damage could still cause a ship to heel or trim to an extent which would affect her manoeuvrability, or prevent her guns from being fired. To correct this, suitable components on the opposite side or end of the ship were flooded, a method used by Cox when ships tended to list during their lift and were in danger of turning over and sinking. Main transverse bulkheads were as far as possible not pierced by doors or any other fittings except essential electric leads and power pipes which were arranged above the waterline.
At the suggestion of an Admiralty official whom Cox had approached with a view to buying the scuttled ships, he had, as told, visited Scapa Flow and decided upon purchase, ignoring the Admiralty’s official pronouncement that the ships were at such a depth that salvage was out of the question. Under a later contract he also acquired the battleships Moltke and von der Tann, the battlecruisers Kaiser and Prinzregent Luitpold, and the light cruiser Bremse.
He loaded the floor of his floating dock with a wide variety of salvage equipment, railway lines, trucks and two crane jibs. Workshops and machinery associated with a floating dock were already in the massive side walls. Compressors, generators and any other necessary equipment were installed. Brackets were fitted on the seaward face of the dock to support 6-inch diameter mild steel shafting. On this shaft were mounted ten grooved pulleys with a diameter of 42 inches to take wire hoisting ropes. Ten hand-operated winches positioned along the dock could be worked in single or double gear. At the back of the dock were anchored pulley blocks with six sheaves of 20-inch diameter. Similar blocks were positioned at the moving end. All these could sustain a load of 100 tons. Liftingwire ropes from the winches were passed through the anchored blocks, and then through the moving blocks, the rope being 1¼-inch diameter. Single wire ropes 2⅜-inch diameter, each capable of a lift of 250 tons, were attached to the moving blocks. Attached to the end of each wire was a Lowmore iron stud link chain of 3½-inch diameter. Two stud chains were installed on deck, each with a lift of 7½ tons at a radius of 75 feet. The vertical back structure was sub-divided into offices, powerhouses, workshops and storerooms. When the long 700-mile tow to Lyness began, £40,000 had been spent on salvage gear.
Much of the salvage and diving equipment was manufactured by the world-famous firm of Siebe Gorman & Co Ltd. Its founder, Augustus Siebe, had invented an ‘open’ diving dress in 1819 which was worn in conjunction with an air pump. It was based on the principle of the diving bell, and air found its outlet at the edge of the jacket. But if the wearer fell, water rushed into his dress, and unless he was quickly brought to the surface he was in danger of being drowned. The closed diving apparatus developed from this early invention, similar to the Hard Hat worn today, was also invented by Siebe in 1837. This was connected to an air pump, also manufactured by Siebe Gorman & Co. Pressure gauges on the pump indicated the depth at which the diver was working and the pressure of air being supplied. The helmet could be connected with the breastplate, or corselet, by a slight turn; the equipment was made of copper or bronze. An air supply pipe was attached to a non-return inlet valve in the helmet. An
air outlet valve fitted to the helmet allowed the diver to control the amount of air in his dress, and thus his degree of buoyancy.
When the diver began work, he adjusted his valve to maintain his equilibrium. In those days there were no self-contained breathing outfits, and skin-diving had yet to come. The thick glass window fitted to the helmet often steamed over. To clear the mist, the diver had to open the top of a small tube, the spitcock, leading to the outside of the helmet, take a quick mouthful of sea water, then close the tap and squirt the water over the misted glass.
Attached to the helmet was a telephone, also introduced by Siebe Gorman & Co. The receiver was in the crown of the helmet and the wires embedded in the life-line. Unfortunately, the procedure for clearing mist usually shorted the telephone contacts and put them out of action.
The dress itself was made of rubberised twill. It covered the whole body from foot to neck, and the sleeves had vulcanised rubber cuffs to provide a watertight joint at the wrists.
The flexible air-pipe, which passed under the left armpit, had to be stout enough to withstand being cut on sharp edges of metal, and it was always liable to be trapped by a fall. Then there was the life-line for use in an emergency, for hauling the diver to the surface, and for signalling by a certain number of pulls or jerks according to a prearranged code.
The diver’s dress was completed by a heavy pair of boots weighted up to 16 pounds each; these enabled him to keep upright in water. He also wore a 40-pound lead weight on his back and another on his chest to enable him to preserve his equilibrium.
Two Admiralty tugs to further the work were bought by Cox and named Ferrodanks and Sidonian. The captain of Ferrodanks had been in Orkney for most of the war carrying water from Stromness to the British fleet.
The floating dock, having completed its long journey to Scapa Flow, was beached at Mill Bay near Lyness. Cox then had one of the great side walls cut away so that chains could be let down over the edge of the platform. As lift would be required from both sides, the dock was cut in two, thus providing two L-shaped docks, each 200 feet in length and 40 feet in width. Each dock was furnished with 12 sets of lifting gear, and each set had a three-gear hand winch and a 100-ton five-sheaved pulley block. It also had five main compartments which could be pumped out separately or joined by means of bulkhead valves. The docks were practically complete power stations. About 65 per cent of the power was generated by dynamos driven by high-speed steam engines, the remaining power being generated by dynamos coupled to, or belt-driven from, internal combustion engines. Eight sets of 6-inch pumps of submersible type were each connected to the machinery room in the dock wall by 100-foot flexible cables covered with rubber sheathing. Power was generated by a 70 kilowatt steam-driven generator set. There was also a 100 brake horsepower direct current motor coupled by a belt to a 60 kilovolt ampère 3-phase generator designed for 50-cycle current at 220 volts. Alternating current was used for working the pumps which were run alternately in pairs. A small 40-cubic-foot compressor was used for the pneumatic tools.
Cox now had the men and the equipment, but everything depended upon team-work, and to that he always paid tribute. The divers, in particular, worked long hours cheerfully, and often in conditions which today would be considered intolerable. Their work was both hard and dangerous, and in those days it was not appreciated that years of diving could affect a man’s heart. One diver, Hall, died in his suit; another. ‘Busy’ Bee, a man perhaps too old for this type of work, died after getting out of one; a third, much later in the operations, after an escape from a nasty situation, was found drowned a few days later though a good swimmer; the diver, James Thomson, who worked on nine of the capital ships raised, and H. Murray Taylor, a salvage officer, were both awarded the MBE for dangerous work successfully accomplished in attaching wires to two live torpedoes which had not been fully discharged from a submarine.
An average man could dive to five fathoms. If his physical condition was good he could descend to ten fathoms. Deeper than that extreme fitness was necessary, while at 20 fathoms only those exceptionally fit could endure the conditions to which the body was subjected. Divers encountered poisonous and explosive gases in the ships. Their air-pipes were liable to be cut on a sharp edge or trapped by a fall. There were the hazards of marine life, too: Harry Grosset was badly bitten on the hand by a conger eel while pushing an air-pipe through a porthole. Conger eels were everywhere. Trapped in a cabin, a grey seal died and was used to play a frightening practical joke upon a new nervous diver. White-faced, the man rushed up to the salvage officer and gasped that a dead sailor lay in a bunk in Hindenburg’s cabin. Told that such a thing was impossible, he took the salvage officer down to prove his story, and there lay the dead seal dressed by the man’s workmates in sailor’s clothing, its tail end covered with a blanket. In one of the destroyers a very large lobster which must have been five or six years old had taken up its home in one of the compartments which it defended vigorously with outsize claws whenever anyone attempted to enter it. T. McKenzie, the chief salvage officer, related an occasion when, inspecting an upturned destroyer at a depth of some 30 feet, he thought another vessel was almost upon him. He flattened himself under the wreck, and soon afterwards a terrific jerk on his breast-rope tore him out, free and unharmed. Then he saw that his near accident had been caused by the flick of a 40-foot whale’s tail. Schools of playful whales became such a nuisance for a time that all divers were called up as soon as they were seen in the vicinity.
As far as possible workers were obtained locally. These trained others on the job, divers especially. The old divers welcomed recruits as the recruit’s first successful dive ended in ‘drinks all round’. But Cox’s most valuable find was his young salvage officer, T. McKenzie, who had been educated at Glasgow High School and had qualified as a member of the Scottish Institute of Civil Engineers. His father, under whom he had obtained his experience and learned how to dive, was a sea captain, the only one in Scotland experienced in salvage work. Among young McKenzie’s varied tasks he had spent two years in the search for a Spanish treasure ship, though only a few pieces-of-eight were found. After enlarging his experience with the Glasgow Trust, he qualified as a member of the Institute of Mechanical Engineers. Another contract took him on salvage work off the West African coast, and it was upon his return in 1923, when he was a foreman diver on the Clyde, that he made the acquaintance of Cox whilst on holiday, through a mutual interest in fresh-water fishing. Cox had just obtained additional financial aid for his salvage venture and, having an eye for a good man, he persuaded McKenzie to work for him. This was the beginning of a brilliant career in salvage work. Cox provided the money and the drive, but without McKenzie’s imagination and technical ability the German fleet might never have been raised. Cox began by engaging about 20 technicians of different skills from Sheerness dockyard, and about the same number from Aberdeen and Glasgow. When work got into its stride he had a labour force of about 200 men. They lived in the old naval camp he had bought at Lyness and speedily evolved their own class distinctions. The aristocracy of the workers, the divers and their mates, lived together in huts; mechanics formed the next group in the social scale, living together in their huts, and lastly the labourers in theirs. These distinctions were jealously preserved. It was almost a womanless world, for there was no married accommodation. At no one time were there more than four wives living at Lyness, the senior of them being Mrs McKenzie, the wife of the young chief salvage officer, who was to spend 24 years in all at Scapa Flow. The main social functions were the dances, and later, when Metal Industries Ltd took over, the banquets after each successful lift.
Cox soon discovered that the Orcadians had been before him. In the tradition of their old Viking forebears they had carried out some unauthorised salvage work on their own account. With the gay abandon of the karate team which recently demolished a derelict house with bare hands, the fishermen, with scarcely more equipment, had removed thousands of pounds worth of fittings and metal, in
cluding a number of gun-metal torpedo tubes then worth £100 each – in fact, anything which could be reached and moved. A few of them had also gone out to Seydlitz, alongside which they had sunk their fishing-boat so that it could not be seen by patrols or watchmen, and had lived aboard while stripping her down to water-level of all brass, gun-metal and copper. On Hindenburg all metal of any value above water had vanished: electricity cables, telephone wiring gear, switches, lamps and even removable brass screws had been smuggled away in barrels labelled ‘herrings’. When Cox decided that the time had come to employ watchmen of his own, he advertised in the local newspaper, and one of the applicants, as a testimony to his knowledge of the ships, stated that he had kept watch for the men who had stripped them. Yet these were the same Orcadians upon whom their future employers could never lavish high enough praise for their loyalty, endurance, courage, skill and resource, and close ties between many of them and the then chairman of Metal Industries Ltd, the firm which virtually ended the work of salvage, still exist.
From Jutland to Junkyard: The raising of the scuttled German High Seas Fleet from Scapa Flow - the greatest salvage operation of all time Page 6
