Winch Operations
- Wire rope
- Often called "cable", it consists of many thin steel wires grouped into bundles to form strands. Multiple strands of wire are then twisted tgether around a core to form a complete wire-rope assembly.
- Wrap
- A single coil of wire rope wound on the drum of a winch.
- Layer
- All wraps of wire rope around a winch drum that are on the same level.
- Capacity
- The capacity of a winch decreases as more layers of cable wrap around the drum.
Every winch has a capacity rating, the maximum load that it can pull. For example, many winches are rated at 8,000 pounds or 20,000 pounds. But this is based on a "first layer" rating. This means that the maximum pulling capacity of a winch is only at the first layer, when all cable is off the drum except the very first layer of cable.
The capacity of a winch decreases as more layers of cable wrap around the drum. For example, a typical 8,000 pound capacity winch actually has five ratings, depending upon which layer of cable is doing the pulling:
- * 1st layer: 8,000 pounds
- * 2nd layer: 6,700 pounds
- * 3rd layer: 5,700 pounds
- * 4th layer: 5,000 pounds
- * 5th layer: 4,500 pounds
As a rule of thumb, deduct 10% off the rated capacity for each layer of cable on the drum. Generally, when all the cable is on a winch, the pulling capacity is only 50% of its full rating. This is a good reason to pull off lengths of wire rope and rig up a pulley system with your winch. Also notice as cable builds up layers on the drum, the speed that the line moves increases to nearly double the first-layer speed.
- Always leave some cable on the drum.
- Always leave a minimum of five wraps of wire rope on the drum at the bottom layer to achieve a rated load. This is a safety feature that keeps the line from pulling completely off the winch drum. Five layers on the drum is the minimum!
- Place a heavy canvas or tarp over winch lines.
- Winch operators should always make sure that everyone keeps well back and away from any winching activity. It is good practice to use a heavy blanket or heavy tarp over the wire rope while pulling. If a rope failure occurs, the weight of the tarp will minimize the whipping of the broken cable. Raising the vehicle's hood can also give some protection should the rope break. The tarp also acts as a visual warning to rescue workers, preventing them from walking into or tripping over the rope.
- Allow slack in the line
- Winch cable on an electric-powered winch should have slack in it when you first start to pull. Very few winch operators are aware of the "slack in the line" rule for electric winches. The Army's official HUMMER training manual advises operators to allow one foot of slack in the cable prior to start of winching operations. This allows time for the motor to get up to speed for maximum pulling power.
- Use proper size of cable
- It is important that the diameter of the winch line is proper for the winch you are using. The largest recommended wire-rope size should be no larger than one-eighth the cable drum barrel diameter. More information may be found at www.innovation-engineering.co.uk.
- Wire rope is identified by two numbers.
- Two numbers, such as "6 x 19", are used to classify the construction of all wire rope. The first number indicates the number of strands that make up the complete wire rope. The second number describes how many wires are twisted together to make each strand.
- For example, a winch cable may be classified as "6 x 19" wire rope. 19 individual wires are twisted to form each strand. 6 strands are then twisted together to form the rope.
Condensed from an article written by Ron Moore, published August 2005 by Firehouse magazine
