Shear legs facts for kids
Shear legs, also called sheers or sheer legs, are a special type of lifting tool. They have two strong legs and are used to lift very heavy things. Think of them like a giant, two-legged crane!
Shear legs can be built in two ways:
- Permanent: These are fixed in one place, like a strong A-frame structure. You often see them on land or as part of large floating cranes.
- Temporary: These can be set up when needed, especially on ships that don't have a regular crane.
When they are built to stay, shear legs are used for really big jobs. This includes lifting parts for shipbuilding, helping to recover tanks, or rescuing things from the ocean floor. At places where ships are built or repaired (called dockyards), they lift tall masts and other heavy parts onto ships. Sometimes, smaller, temporary shear legs are even used on sailboats for similar tasks.
Contents
How Shear Legs Are Used
On Land
Shear legs are a bit like other lifting tools such as a gin pole or a derrick. They are made from two strong pieces, like wooden beams or metal poles, set up in an A-shape. The bottom of the legs rests firmly on the ground so they don't move. The top of the A-frame is held steady by strong ropes or wires called "guys."
Unlike a gin pole which needs at least three guys, shear legs usually only need two. This makes them a bit simpler to set up in some situations.
On Water
The biggest and strongest shear legs are often found on special floating cranes. These are known as floating sheerlegs. They have very large A-frame arms that can lift incredible weights, from 50 tons up to 4,000 tons!
These giant floating cranes are mainly used for:
- Building large ships.
- Putting together other big structures.
- Moving very heavy cargo.
- Helping with salvage operations, like lifting sunken objects from the water.
Temporary shear legs on a ship are made from two tall poles tied together at the top. The bottom ends of the poles are spread apart. Unlike a three-legged gyn (which is stable on its own), shear legs need a strong rope, called a "guy," to keep them from falling over.
The point where the two poles cross and are tied together is called the "crutch." This is where the block and tackle (a system of ropes and pulleys for lifting) is attached. Shear legs are stronger than a single-pole derrick of the same size. Also, the crutch of shear legs can be moved up or down a little bit, which helps with positioning.
A long time ago, when sailing ships were common, dockyards often used a special kind of ship called a sheer hulk. This was an old ship's hull that had shear legs built onto it. It was used to install the tall masts into new ships.
See also
- Crane (machine)
- Masting sheer
- Sheerleg
