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A ballast tractor is a heavy haulage road vehicle designed to pull or push heavy or exceptionally large loads. Unlike the tractor unit from an articulated trailer, the ballast tractor is designed or adapted to pull or push loads from a drawbar. By contrast an articulated tractor unit pulls from a "fifth wheel", and only pushes when reversing its load.

Description

The name ballast is derived from the nautical term (see sailing ballast) describing heavy material added to a vessel to improve stability. With a semi-trailer, the weight of the trailer presses down through the fifth wheel and adds ballast. In the case of a ballast tractor, the drawbar only transmits a horizontal force to the load, which is supported separately. Ballast is added over the driving wheels to increase the available tractive effort. The weight increases the friction between the tyres and the road surface. Without such ballast, the tractor would be unable to overcome the inertia of a heavy trailed load, and its wheels would rotate without generating forward motion. Ballast tractors tend to have high power engines and engines that provide lots of torque, even at low speeds which is more important. Ballast tractors are often fitted with heavy duty hub reduction axles, or high reductive gear boxes to increase torque at the wheel. Therefore heavy duty ballast tractors tend to have low maximum speeds. It is commonplace to find ballast tractors with a torque converter and extra coolers among other things.

A ballast tractor can be either a modified tractor-unit, or the truck itself can be built from the ground up to be a ballast tractor. The tractor-unit variants tend to be heavy versions of readily available commercial models; such models have increased chassis strength to accommodate extra ballast and drawbars. A ballast tractor that is built as a ballast tractor tends to be the heaviest class of on-highway trucks. In some cases, the chassis alone of these trucks can be even greater than their axle configuration legal GVW, so require special permission to use the roads.

Ballast tractors tend to have their ballast located across their driving axle. The ballast on multi drive axle machines is designed such that the desired axle load per axle is achieved to avoid overloading a particular axle. Modern ballast trucks, which tend to be modified heavy duty versions of normal tractor-units, tend to have two or more driven axles (such as 8x4 configuration). Heavier ballast tractors tend to have all wheel drive. The heavier variants of ballast trucks, which tend to live their lives with permanent ballast (or high weights), have strong heavy chassis. Having a ballast truck with a high curb weight means that the truck may be already beyond the maximum permitted GVW and requires special permission even in this state. An advantage of such a machine allows ballast to be added when the demand is there (such as moving a heavier load).

Uses

A ballast tractor is somewhat limited in its use in modern day road freight because tractor-trailer combinations are more flexible and practical to move normal heavy loads. Heavy duty tractor units that are equipped with temporary ballast boxes can also often be used as a normal fifth wheel based tractor-unit, but its curb weight is often too high thus reducing the payload of the entire vehicle. A ballast tractor on its own is usually too heavy to be used for normal transport because the payload of the truck and its trailer are reduced considerably.

The main use of ballast tractors has been that of moving heavy and abnormal loads. Ballast tractors tend to have high traction, which enables them to move a heavy load without losing power via wheelspin. Because ballast tractors tend to have reinforced chassis, they can be coupled together to increase power and traction. Normal trucks can not do this for heavy loads, as their chassis is being tugged from both sides hence likely resulting in a fracture. Another advantage of using ballast tractors with abnormal loads is that one can be used to push steer a trailer around a corner. A girder trailer for example is double articulated so the front tractor can pull the load around a corner whilst the rear tractor can push the rear end (at an angle) around the same corner. Therefore a push/pull combination can make an abnormal load more maneuverable than a rigid solution pulled by several tractors.

Another specialized use for ballast tractors is in showman vehicles. The ballast tractor used in this case may be a typical tractor unit fitted with a ballast box used to tow specialized trailers that contain rides which may not fit onto a standard fifth wheel connecting trailer, or is more convenient. The vehicle is used in the same manner as described above, but the overall weight is much less to comply with vehicle weight legislation, particularly axle loads. Sometimes, particularly on older machines when GVWs were lower, a generator set may act as the ballast. Today, generators can fit on the back of a tractor unit. Ballast tractors are not often seen in fairgrounds today.

Manufacturers

There are few well-known manufactures that produce ballast tractors that are built as such. Most high-volume manufacturers offer heavy duty chassis versions of some of their tractors, which enable a ballast box to be fitted. In Europe, manufacturers tend to send some of their products to another company (owned by the parent) to be converted into a special heavy duty version.

There are a few companies that do build built-to-order machines which tend to be the heaviest and most powerful machines designed for one company for a specific purpose. Nicolas Tractomas (France) for example, currently builds 8x8 and 10x10 ultra heavy duty tractors for Rotran in South Africa.

Ballast tractors were more popular in the past in developed countries, due to a larger volume of heavy goods being produced for modernization schemes and expansions.

Canada



Czech Republic



France



Germany



Netherlands



UK



USA



Operators

Most heavy haulage firms employ heavy duty tractor-unit models that can accommodate a ballast box.However, some of those associated with heavy lift engineering such as Mammoet and A.L.E do operate a number of heavy duty ballast machines. Countries where modernization is taking effect, such as regions of the Middle East and South Africa, operate larger number of ballast tractors due to the greater frequency of heavy loads (such as power station components).

UK

Apart from being used by fairgrounds as a direct replacement for the steam-powered showman's engine, specialist moving and haulage companies use ballast tractors. These include:

Alternatives

With the increasing versatility of Self Propelled Modular Transporter (SPMT) and modular low loaders, pure ballast tractors are not as common, with most being a heavy duty tractor unit with a removable "Ballast" box fixed in place of the fifth wheel unit. Ultra heavy loads of 200 ton plus generally are only moved short distances and SPMT's are more manuverable. Items commonly moved include: oil rig modules, bridge sections, buildings, sections of ships, industrial machinery.

See also



References

  1. High, Wide & Heavy by David Lee, Published by Round Oak, ISBN 1-871565-47-2


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