A winch is a mechanism used to reel in, to let out, or otherwise adjust the tension of a rope, wire, or cable. Boats and ships make use of multiple winches to handle halyards, sheets, as well as anchor or mooring lines. The basic mechanism consists of a spool or winch drum to wind in and store the line. The line can be manipulated by something as simple as a hand crank, but larger winches may incorporate gear assemblies and are powered by electric, hydraulic, pneumatic, or internal combustion drives. Some use a mechanical or a solenoid brake to control the line; occasionally a ratchet and pawl setup prevents the spooled line from unwinding. Some types of winches, commonly referred to as "self-tailing", make use of a "stripper" or cleat to maintain the proper level of tension on the line.
In larger forms, winches form the mechanical base of tow trucks, steam shovels, cranes, and elevators. Outside of their marine and industrial uses, winches are used to tow all kinds of vehicles. Planetary winches and worm gear winches are two winch types currently in use for this purpose. Planetary winches are commonly found on the front of road vehicles such as trucks and SUVs. They have a fast line speed, but should be restricted to light duty. A worm gear winch is designed to have a slower, consistent pull in order to hold a heavy load. These types of winches are usually seen on car hauling trailers, and larger work trucks.