Mechanical skidding has become the mainstay ORT method of the forest industry in Canada and around the world. Almost every industrial forest harvesting operation uses mechanical machines to skid wood from the stump to the landing. The most notable exception would be cable logging used in parts of British Columbia. Mechanical skidders were initially four wheel drive farm tractors. It is likely that tractors were introduced in the woods as a natural extension of the horse logging system. A cable winch with chokers was added on the rear of the tractor to enable it to drag as many trees as possible. Then the frame was made heavier and more durable as the horsepower of the first skidders as we recognize them were born.
Overhead costs of barns, feeding, rest periods, and veterinarian bills, and a shortage of experienced teamsters were likely some of the reasons that a mechanical power supply replaced horse logging in Eastern Canada. Technological advances meant that machines could be used in more demanding situations and not continuously be broken down. They could pull heavier loads over longer distances and at the end of the day, they could simply be turned off. This was a big advantage to companies that might have needed a hundred horses to carry out the work of twenty skidders [is this true ?].
A mechanical skidder is a self propelled machine that drags or skids trees or some portion of the tree to roadside. It is self propelled in that it has an engine that creates power that turns the wheels or tracks that causes motion. A mechanical skidder is an articulating machine. That means that the steering of the machine is carried out by moving hydraulic cylinders in or out at a joint located between the front and rear axles of the skidder. The front wheels do not turn as they do on a car or truck or like a bulldozer. Articulation also dramatically increases the maneuverability of the machine since articulated machines can make sharper turns than normally steered machines. This increase in maneuverability is very important in the woods where tight cornering is often necessary to ensure that standing trees are not damaged. The pivot point or point of oscillation is also important since it allows the front and rear of a mechanical skidder to move independently of one another when the machine runs over a high object like a boulder or high tree stump. The front end is able to twist as one wheel rides over the obstacle which the wheels in the back remain on the ground to provide traction. A machine or vehicle without this feature is not able to move as easily in rough terrain.
Hydraulics
Another important feature of a skidder is the hydraulic power system. Hydraulics deals with the pressure across an area which is delivered through a liquid to create a force. Three components are needed in order for a hydraulic system to function; a pump, a hose and an actuator (or cylinder). The pump creates force by pushing a liquid through the hoses, the hoses transmits the force to the desired location and the actuator creates a mechanical output or a desired movement. To learn more about hydraulics look for books on fluid power or a book on hydraulic power. The hydraulics on a skidder is responsible for making almost everything work. The winch/grapple/clam is moved by a motor run by hydraulics, the skidder changes direction by hydraulics, the wheels spin because of hydraulics and the blade usually found in the front of the skidder is raised and lowered by hydraulics. All forest operations equipment rely heavily on hydraulics to carry out their purpose. [literature cited section here]
Cab
All mechanical skidders have a cab or cage in which the operator sits when operating the skidder. The cab functions in many different ways. It provides protection from falling debris or in case the machine rolls over. It can also protect the operator from the weather such as direct sun or freezing cold temperatures. It can in some cases reduce the level of noise that reaches the operator. The cab is also a place to store important equipment such as fire extinguishers and any tools that might be needed to carry out simple repairs. There is often lighting in and outside the cab to help the operator see at night.
Engine
The engine in a mechanical skidder provides the power for all equipment. Mechanical skidders have engines ranging in size from 130 horsepower (93 Kw) to 200 horsepower depending upon the size of the machine. The engine in most new skidders are four stroke turbo charged diesels that have total displacements from 7 liters (454 cu. in.) to 14 liters of displacement.
There are essentially three types of mechanical skidders. Each has a particular niche or set of circumstances that makes it the most appropriate off-road-transport machine. [what are they ???] However they all have one trait in common, they skid logs or trees along the ground to get them from stump area to the landing. The three types are: cable skidder, grapple skidder and clambunk skidder. There are other kinds of mechanical skidders. A farm tractor can be a mechanical skidder although it would not have all of the features that are mentioned above. There are also types of mechanical skidders that have tracks rather than tires which would also not fit the description given above.