On the top side, the two legs are connected together by a lashing but with a small spacer block placed between the legs. A sling, which may be made from ropes, is placed around the area that two legs meet to be used to put a tackle pulley system for lifting the load. There are two guy wires, front and rear, to support the shear legs. The rear guy may be reeved to allow adjustment of the angle of the shear legs.
|
|
Sheerlegs mounted on an M32 tank recovery vehicle Shear legs, also known as sheers, shears, or sheer legs, are a form of two-legged lifting device. Shear legs may be permanent, formed of a solid A-frame and supports, as commonly seen on land and the floating sheerleg, or temporary, as aboard a vessel lacking a fixed crane or derrick. When fixed, they are often used for very heavy lifting, as in tank recovery, shipbuilding, and offshore salvage operations. At dockyards they hoist masts and other substantial rigging parts on board.
|
|
Shear legs are a lifting device related to the gin pole, derrick and tripod (lifting device). Shears are an A-frame of any kind of material such as timbers or metal, the feet resting on or in the ground or on a solid surface which will not let them move and the top held in place with guy-wires or guy ropes simply called "guys". Shear legs only need two guys whereas a gin pole needs at least three. The U. S. Army Field Manual FM 5-125 gives detailed instruction on how to rig shears.
|
|
Illustration of carpentry (charpente) in the French Encyclopédie showing hewing, mortising, pit sawing on trestles. Tools include dividers, axes, chisel and mallet, beam cart, pit saw, trestles, and bisaigue . The men talking may be holding a story pole and rule (or walking cane). Shear legs are hoisting a timber.
|
|
The shear legs are put in place. The chair is attached to the endless whip and raised to the tower. When everything on the ground is set, the coxswain signals the tower. One member of the tower crew gets in the chair and sits down, clips in, and signals the ground crew.
|
|
The colossal shear legs was visible from afar and the wooden dry dock made a good impression. There was a coal station at Kuiper , and it was brought closer to Onrust by a Bamboo bridge. On Onrust there was a big round Martello-like tower with heavy pivot guns. Fresh supplies were shipped from Batavia on a daily basis.
|
|
A second method is to attach two poles called shear legs in an A-frame configuration with poles running from the sheer to meet above the boat. The mast can then be hauled upward using the forestay. This method requires additional equipment. A third method is to attach a pole to the winch post on the trailer and haul the mast upwards once again with the forestay, which also requires additional equipment.
|
|
1600 ton maximum lift capacity sheerleg Taklift 7 of Smit Internationale A floating sheerleg (also: shearleg) is a floating water vessel with a crane built on shear legs. Unlike other types of crane vessel, it is not capable of rotating its crane independently of its hull. There is a huge variety in sheerleg capacity. The smaller cranes start around 50 ton in lifting capacity, with the largest being able to lift 10,000 tons.
|
|
Then the concrete foundations were poured, and the base plates for the columns were set into them. Once the foundations were in place, the erection of the modules proceeded rapidly. Connector brackets were attached to the top of each column before erection, and these were then hoisted into position. The project took place before the development of powered cranes; the raising of the columns was done manually using shear legs (or shears), a simple crane mechanism.
|
|
A new shear legs was made, the optical telegraph was repaired and the barracks for sailors was improved. Except for the graving dock all this was complete before Van den Bosch left the East Indies in April 1848. Inner court of the Dutch barracks 1912 Onrust now became a good place for commercial ships to dock, and so they did. Soon a massive coal station was established at nearby Kuiper Island (Cipir Kahyangan) which attracted even more traffic.
|
|
By then the number of buildings on the island had increased from 24 to 80. On 5 June 1878 SS Prins Hendrik of the SMN, a shipping line which was also a shareholder of the NIDM, became the first ship to use the port. The repair shipyard included a shipyard with all kinds of machinery, a shear legs and a coaling station. The one crucial asset that was still missing was a dry dock, but this was under way.
|
|
The shears would then be moved along and an adjoining bay constructed. When a reasonable number of bays had been completed, the columns for the upper floor were erected (longer shear- legs were used for this, but the operation was essentially the same as for the ground floor). Once the ground floor structure was complete, the final assembly of the upper floor followed rapidly. For the glazing, Paxton used larger versions of machines he had originally devised for the Great Stove at Chatsworth, installing on-site production line systems, powered by steam engines, that dressed and finished the building parts.
|
|
1600 ton maximum lift capacity sheerleg Taklift 7 of Smit Internationale Fixed shear legs are most commonly found on floating cranes known as floating sheerlegs. These have heavy A-frame booms and vary in lifting capacity between 50 and 4,000 tons, and are used principally in shipbuilding, other large scale fabrication, cargo management, and salvage operations. Temporary sheers comprise two upright spars, lashed together at their heads and their feet splayed apart. Unlike in a gyn, which has three legs and is thus stable without support, stability in sheers (derricks, and single-legged gin poles) is provided by a guy.
|
|
Shearleg derrick is similar to breast with an exception that instead of fixed guy wires that secure the top of the mast, it is secured by multiple reeved guy to permit handling loads at various radii by means of load tackle pulley system suspended from the mast top. In a simpler construction, a shearleg derrick can be assembled from two posts to form A-frame shear legs without any crossbar. The bottom of the legs are set in two holes on the ground spreading them apart. There is a rope to tie the two legs together near the bottom to prevent them from spreading apart further.
|
|
He noted, however, that the time could have been reduced if the workers had been divided into two groups for some of the smaller stones. Concluding his examination of this issue, he argued that "83 journeys by the whole team would have been required, giving an actual construction time of c 137 hours, or 3735 manhours." Adding to this "210 manhours" for digging the post holes for the boulders, as well as "40 manhours for cutting timber and making the shear-legs and sledges", and "another 40 for fetching and trimming the timbers", Lambrick concluded that a total of around "4035 manhours" would have gone into the construction of the stone circle. This would have been about three weeks' work for around twenty workers.
|
|
In Sea Scouts, use of a breeches buoy has become one of the events that are competed in at regattas such as the Old Salts' Regatta and the Ancient Mariner Sea Scout Regatta. The competition simulates an actual breeches buoy rescue situation. Before the event the crew sets up their equipment, which includes a thin shot line attached to the tower simulating the crow's nest of a sinking ship, a high line made of a hawser, a block and tackle, a deadman with a cleat, an endless whip with a block, a chair, and shear legs. Once the equipment is prepared, two scouts go up to the tower (these scouts must wear harnesses for safety in most of today's competitions).
|
|
A gin pole being used to install a weather vane atop the 200 foot steeple of a church Roof trusses being erected with gin poles The gin pole is derived from a gyn, and considered a form of derrick, called a standing derrick or pole derrick, distinguished from sheers (or shear legs) by having a single boom rather than a two-legged one. Gin poles are also used to raise loads above structures too tall to reach with a crane, such as placing an antenna on top of a tower/steeple, and to lift segments of a tower on top of one-another during erection. When used to create a segmented tower, the gin pole can be detached, raised, and re-attached to the just-completed segment in order to lift the next. This process of jumping is repeated until the topmost portion of the tower is completed.
|
|