A low loader, also known as lowboy or float, is a variation of the classic flat bed design specially engineered to carry indivisible freight. It can be loaded from front or rear – depending on design and local legislation.
Featuring a significant drop in height just after the gooseneck, it is extremely low compared to the standard flat platform design and can accommodate even the most challenging freight, such as construction and mining machinery, wind farming equipment and prefabricated sections for a building site.
Most often, the main loading space, located between the gooseneck and the trailer’s axle group, is hovering less than a metre from the ground, and the area above the fifth wheel and gooseneck is used for equipment storage.
Most low loaders are supported on a multiplicity of tyres small enough in diameter to fit beneath the platform. It is common to use 32 wheels, often arranged in four rows of eight wheels each. A complex system of load-equalisation apparatus then connects the wheels to ensure that the load is spread evenly across the wheels and avoid any mismatch.
Due to the unusual freight task it has to handle, the design of a low loader can vary widely. For instance, some companies utilise a single axle assembly as known from mining equipment in place of the common multiple-axle design.
In addition, some companies also offer a steerable axle system – either hydraulically enforced or friction based. The steering actuation of a friction steering model is realised by frictional force, which results from the axle load when cornering. Typically, a pneumatic reversing interlock is integrated into the system in order to provide the necessary rigidity of the friction steered axle when reversing. Compared to an un-steered vehicle, the friction steering system can improve both cornering and tyre wear.
Force-steered axles, meanwhile, are usually hydraulically operated. An adjustable steering key on the fifth wheel coupling serves to transfer the steering angle hydraulically to the semi-trailer chassis. German company Goldhofer, for instance, has implemented this hydraulic steering actuation system by means of a flat slide valve design with guides. The steering is designed as a hydraulic twin-circuit steering system to ensure that even in the event of failure in one of the steering circuits, the continued safe function of the steering system is guaranteed. In addition, the hydraulically enforced steering system offers the option of manually readjusting the steering, in order to manoeuvre the semitrailer independently from the truck.
Most companies, such as Australian expert Drake or New Zealand’s TRT, also offer a liftable, widening or extendable low loader version, and include special equipment such as rail tracks on demand to cater for intermodal transport, for example.
The structure of the gooseneck can also vary significantly. While some rely on a fixed gooseneck to increase deck length and save weight, some bank on a mechanical or hydraulic alternative. The fixed neck solution is lightweight, but may sacrifice the ability to detach and load over the front. The hydraulically detachable solution, meanwhile, can remove the entire gooseneck section so a large piece of equipment can be driven onto the deck over the front. The same system is also available in a rugged mechanical version. Finally, there also is a folding gooseneck design where the deck can be lowered to ground level to simplify the loading process.
Whatever the specification, the low loader’s most impressive achievement is accommodating exceptionally long, wide, high or heavy freight while still meeting the stringent regulations of a certain region. In that sense, it is safe to say that the low loader is the world’s strongest trailer type.