Several years prior to World War II the manufacturing company of Demag A. G. in Duisburg, Germany, received an order from the German Navy to build several giant, self-propelled, floating cranes. About this same time the U.S.S.R. placed an order with the same company for several floating cranes of 350 tons maximum capacity. The result was that the Demag Company undertook the construction of the largest-type floating crane ever built by man, four huge floating cranes of 350 metric tons maximum capacity. One of these four cranes is now a part of the regularly used facilities of the United States Navy at the Long Beach Naval Shipyard.
The crane is a landmark to the City of Long Beach; its lofty 374 ft. high structure, corresponding to a thirty-story building, can be seen from miles around. The 5,000-ton structure sits on a pontoon which measures 205 ft. by 110 ft. Up to a height of 102 ft. above water no portion of the crane’s superstructure extends beyond the edge of the pontoon, thus preventing collision of the rotating superstructure with vessels tied up alongside.
The crane has five hooks. The two main hooks are each of 175 tons capacity. During lifting operations if the mechanical brakes should fail while holding a load suspended, the motors will act as generators and dynamic braking will ease the load down, thus preventing a violent crash. Two smaller thirty-ton trolley-operated auxiliary hooks effect small radial displacements of a load suspended by the main hooks. A smaller ten-ton hook travels up and down the main boom and is normally operated vertically over the main hooks to allow small loads or heavy cables to be raised to or attached to loads already suspended from the huge main hooks.
When the crane is trained on the beam, a maximum lift of 350 tons can be accomplished 59 ft. from the side of the pontoon, or at a maximum radius of 157 ft. from the side of the pontoon, fifty tons can be lifted. Maximum working heights for the main hooks are 170 ft. above water and 26 ft. below.
Maximum speed of the self-propelled vessel is 6.7 knots. Cruising speed is five knots. Performance underway, particularly maneuverability, has proved to be excellent. The critical factor—but, of course only in the open ocean or an open roadstead in a strong wind—is transverse stability. The righting arm is a maximum at 12° and becomes zero at approximately 30°. Consequently, roll in excess of 12° is considered extremely hazardous. The vessel’s period of roll of 10.8 seconds corresponds to the wave period often encountered in the swells of the ocean. It is because of this fact that the crane’s operation is restricted to sheltered water such as the man-made Harbor of Long Beach, where she has remained since her arrival in 1946.
The Germans felt that providing the new crane with adequate self-propulsion would be much easier than using tugs around her in a crowded work area. The designers were not greatly interested in speed; they wanted maneuverability and particularly the ability to hold course in a light wind. For this reason they chose to equip her with their newly-perfected Voith-Schneider propulsion. YD-171 is equipped with three six-bladed, vertical-axis, variable-pitch, cycloidal, Voith-Schneider propellers. Each propeller is actually a solid wheel upon which are mounted six 180 cm. bronze blades on a circle of 260 cm. diameter. The wheel is installed inside of the pontoon so that its bottom face is flush with the shell plating. The six blades hang vertically downward from the wheel. As the wheel rotates, each blade oscillates about its own center because of a system of connecting rods from a common off-center steering center, thus introducing variable-pitch. The result is that the blades thrust in the direction desired and then feather until in position again. Control can be effected by changing the position of the steering center, accomplished by means of two auxiliary motors. One motor effects changes in fore-and-and-aft thrust, producing speed control. The other motor effects changes in transverse thrust, producing steering control. This propeller thus provides two obvious advantages over screw propellers—the vessel can maneuver without reversing engine or drive-shaft rotation, and the propeller combines drive and steering.
It is interesting to note that the Germans later installed two retractable Voith-Schneider propellers near the bow of one of their aircraft carriers, the Graf Zeppelin, to increase her maneuverability for passage through the Kiel Canal. This ship was building at Hamburg during the last years of World War II but was never completed. During the War the United States Army and Navy became increasingly aware of the outstanding performance of German minesweepers equipped with Voith-Schneider propellers. In 1944 the Army and Navy began development of vertical-axis propellers. By the end of the War we had captured a German minesweeper equipped with two Voith-Schneider propellers; soon thereafter we acquired YD-171. Progress on the development of these propellers has continued in the United States since that time until at the present a 300 ft. Army beachlighter, similar to an LST, is being equipped with two Voith-Schneider propellers. General use of vertical axis-propellers is not contemplated, however; they are particularly applicable to vessels requiring a high degree of maneuverability, such as mine locator vessels.
Construction of four sister cranes began in 1938. The crane which came to the United States was completed in June, 1942, at Bremerhaven at an estimated cost of $3,500,000.
She saw considerable service during the War in the Baltic Sea, in north-German seaports, and in Denmark. Toward the end of the War she was used in submarine construction and repair at the submarine base at Kiel, where she underwent several bombings and received some damage. In May, 1945, YD-171 and a sister crane fell into British custody with the capture of Kiel. A third, uncompleted crane was captured by the Russians. Construction on this crane, originally intended for Russia, had ceased with the German invasion of that country. The fourth had been sunk at Hamburg.
Under authority of the Tri-Partite Naval Commission one crane was awarded to each of the Big Three Allies. The British attempted to move their crane across the English Channel but lost her when she capsized in the rolling sea. The Russians moved their partially completed crane overland to Danzig and she has not been heard of since that time. The crane at Hamburg remained resting on the bottom in about twenty feet of water for some time. Finally she was raised, and in 1951 she was bought by French interests from her German owners. On June 25 of that year, while being towed from Flensburg to France, she capsized and sank in the Skagerrak.
In early 1946 the Americans prepared to move their crane to Bremerhaven via the Kiel Canal. The boom and much of the superstructure were removed in order for the crane to clear bridges over the Canal. In May, 1946, the crane arrived in Bremerhaven where she was to be used by the Army to clear the harbor. About this time the crane was requested by and transferred to the Navy for towing to the United States and assignment to the Long Beach Naval Station, California. The Army had to content itself with its captured 250-ton crane.
The crane was placed in the North-German-Lloyd Shipyard in Bremerhaven where preparations were made for the ferry trip to the United States. A thorough investigation and analysis were made to determine the strength and stability of the crane under conditions of ocean towing. As a result of this investigation, additional superstructure was dismantled; the crane still towered 130 ft. into the air, however. The dismantled superstructure previously stowed on deck was removed. The three propellers and their motors were taken out, and the resulting holes were covered with steel plates. Keel plates and the shell plating were reinforced. Finally, a tow chain was installed. The removed superstructure was loaded aboard the USS Lindenwald (LSD-6) for shipment to Long Beach.
The Atlantic tow began on August 14, 1946, with two seagoing tugs, ATF 156 and ATF 160. One tug towed while the other stood by. In order to keep the pontoon steady the forward safety tanks were flooded and sea anchors were put out. Twice during the crossing the pontoon was cut free because of heavy seas. On September 20 she arrived at Cristobal, Panama Canal Zone, after being towed for five weeks at an average speed of five knots. Here the thirteen-inch fenders of the 110 ft. 2 in. beam pontoon were removed in order for the pontoon to clear the 110 ft. wide Canal locks for passage. On October 7 the crane was towed through the Canal by three Canal tugboats and, on October 8 she was moored in Balboa Harbor, awaiting the Pacific tow. On October 30 ATF 104 took her in tow with ATF 102 standing by. On November 18 the crane arrived at Long Beach and was moored inside the mole at the naval shipyard.
About this time the Lindenwald also arrived at Long Beach. Her deck cargo was soon unloaded, except for the 175-ton butt section of the main boom (the heavy section at the foot of the assembled boom). Lifting facilities at Long Beach were not capable of lifting this heavy structure. As a result, the Lindenwald proceeded to the Hunter’s Point Naval Shipyard, San Francisco, where the butt section was unloaded and placed on the deck of the crane-ship Kearsarge (AB-1), which was then engaged in re-gunning a battleship. The Kearsarge was towed to Long Beach in May, 1947. All component parts of the crane were now located in Long Beach.
At this point several engineers set about drawing up new plans of the crane to be used in reassembly and new operating instructions. The original papers had been lost or burned by the Germans. Considerable time was also spent in translating the various German nameplates and inscriptions scattered throughout the vessel.
In November, 1947, after the top section of the pintle tower (the superstructure which supports the boom) had been erected (see Fig. 3), the vessel was placed in drydock and the bomb-damaged portions of the hull and superstructure, temporarily repaired in Germany, were renewed as necessary. After the fenders had been replaced the entire hull was painted, and the vessel was undrydocked. Meanwhile, the booms and their component parts were laid out, repaired, and completely painted.
The first problem of the assembling job was restepping, placing in position the butt section of the main boom. The Kearsage had a lifting capacity of 250 tons, but it could not lift high enough to restep the butt section with YD-171 in the water alongside. The solution was to place YD-171 in drydock at the extreme seaward end near the caisson. The Kearsage, tied up just outside the caisson, could lift over it. By this scheme nearly fifty feet of vertical lift was gained. The crane was placed in Drydock No. 1 on April 27, 1948.
Even this solution was not completely adequate, however. In addition, it was necessary to plan the lift for the time of the highest tide of the year. This scheme, engineers calculated, with every other factor in their favor, would give them a lifting-clearance of four inches. On the appointed day, though, when the butt section was raised to the assembly position, there was no clearance; in fact, the lift was one-half inch short. A Navy tug was called and ordered to run full speed alongside the Kearsarge to create a swell. This maneuver caused a gain of about two inches, and, although clearance was small, the gain was adequate.
There was yet a further problem to be solved before restepping could be accomplished. YD-171 and the two assisting 56-ton dockside cranes were stable; the Kearsarge, afloat and rolling, was not. The butt section was held in place by two 1500 lb. pins, one on either side. It was necessary to place this structure squarely in place and to drive home these two pins at the same instant. Otherwise, the structure might be buckled. Obviously, the Kearsarge could not be held steady. Coordination of motion was the only practical solution. Engineers observed the slight motion of the Kearsarge. On a chosen three-inch surge the structure was slipped into place and the two pins were driven home.
On this day, as on many to follow, operations were hampered by strong winds. The wind not only swayed the suspended structure, making delicate positioning difficult, but also made conditions more precarious for the men working at such great heights.
Work continued for three weeks (see Fig. 4) until finally the linkages were connected to the booms, and the Kearsarge was released from supporting their weight. Riggers then set about rigging the more than two miles of cable, and soon this job was completed also. Not a single man had been injured during the entire hazardous assembly operation.
The remaining small jobs were completed in the early summer, and in August the exhaustive tests commenced. On August 18, 1948, the crane reached out 59 ft. from the port side of the pontoon and lifted a record-breaking test load of 385 tons (425 short tons of 2,000 lb. each). (See page 1288.) Heel was slightly less than 4°30ʹ.
On December 31, 1948, YD-171 was placed in operation. Crane reconstruction had cost only $300,000, while the crane was valued at $3,000,000.
Since 1949 YD-171 has proved her usefulness in many ways. Her greatest asset is her mobility, being easily moved to any point within the harbor where her services are needed. This mobility is extremely advantageous for ship conversions, for lifting turrets and handling guns, for installing boilers and reduction gears, and for many unpredictable needs.
The crane averages about 500 working hours per year. Among her many lifts she makes about forty each year of a hundred tons or over. An additional yearly average of twenty lifts are made because of her extreme reach capability; without her it would be necessary to place the various vessels concerned in drydock in order to permit the land cranes to reach the location of the required work. An average of five lifts per year are made for commercial concerns located in the Long Beach Harbor area, at a rental rate of approximately $10,000 per day.
In my opinion, YD-171 has proudly earned the title of Hercules of the U. S. Navy.
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SEABEE TIMEPIECE
Contributed by COMMANDER RICHARD F. ARMKNECHT, C.E C., U. S. Navy (Retired)
It was in the early days of the occupation of Berlin, when the “operators” among the American troops often wore several wrist watches on each arm—to be traded for Occupation currency, with which the Russians were so well supplied. An American Sea Bee, sporting a cane he had made during his spare time, was accosted by a Russian, who wanted to buy a watch.
“But I tell time with my stick,” said the Sea Bee, and drawing a rough sun dial, Boy Scout fashion, on the ground, he stood the cane up in the proper position and showed how the sun’s shadow counted the hours.
He sold the cane!
★
LIMITED FACILITIES
Contributed by CAPTAIN EDMUND A. CRENSHAW, JR., U. S. Naval Reserve (Retired)
During the peak of the World War II emergency the need for torpedoes was extremely acute and it was necessary to let sub-contracts for parts and assemblies to civilian contractors, none of whom had ever made torpedo parts before, and most of whom were entirely unfamiliar with Government contract procedures.
After a number of such contracts had been let by the Torpedo Station at Newport, a letter was sent to all contractors calling their attention to the necessity of submitting detailed drawings of all jigs and fixtures when requesting payment for this part of their work.
A few days later a letter was received from one of these firms which referred to this requirement and continued, “We are a small concern with limited facilities for grafting and would appreciate being relieved of the above requirement.”
The following morning a special delivery letter was received which read:
“Please change third word in line two of the second paragraph of our letter of yesterday to read drafting.”
(The Proceedings will pay $5.00 for each anecdote submitted to, and printed in, the Proceedings.)