Towing
Towing is coupling two or more objects together so that they may be pulled by a designated power source or sources. The towing source may be a motorized land vehicle, vessel, animal, or human, and the load being anything that can be pulled. These may be joined by a chain, rope, bar, hitch, three-point, fifth wheel, coupling, drawbar, integrated platform, or other means of keeping the objects together while in motion.
Towing may be as simple as a tractor pulling a tree stump. The most familiar form is the transport of disabled or otherwise indisposed vehicles by a tow truck or "wrecker". Other familiar forms are the tractor-trailer combination, and cargo or leisure vehicles coupled via ball or pintle and gudgeon trailer hitches to smaller trucks and cars. In the opposite extreme are extremely heavy duty tank recovery vehicles, and enormous ballast tractors involved in heavy hauling towing loads stretching into the millions of pounds.
Necessarily, government and towing sector standards have been developed for carriers, lighting, and coupling to ensure safety and interoperability of towing equipment.
Historically, barges were hauled along rivers or canals using tow ropes drawn by men or draught animals walking along towpaths on the banks. Later came chain boats. Today, tug boats are used to maneuver larger vessels and barges, and offshore and salvage tugs are used to tow unpowered or disabled vessels over long distances. Over thousands of years the maritime field has refined towing to a mathematics.
Aircraft can tow other aircraft as well. Troop and cargo-carrying gliders were towed behind powered aircraft, which remains a popular means of getting modern leisure gliders aloft.
Types of trailers
This section refers to the towing of a cargo-carrying device behind a truck or car.Most trailers fit into one of three categories:
- Small trailers that attach to cars and small trucks :
- * Small enclosed trailers are fully covered by four sides and a roof. These types of trailers are generally used for carrying livestock since they protect the contents from weather. People also rent these types of trailers for moving boxes, furniture and other materials.
- *Boat trailers are used specifically for pulling boats. These types of trailers are designed for easy loading in and out of the water and are purchased based on the specific type and style of boat they will be hauling. They are open trailers that are specially shaped to hold and secure boats; because of this specialty, they are a unique category.
- *Recreational vehicles are utility vehicles or vans that are often equipped with living facilities. While some are self-propelled, many are designed as trailers to be attached to a trailer hitch. These trailer hitches are common on the back of many cars and trucks, and RV trailers are commonly used for camping outings or road trips. In the United Kingdom, RV trailers are known as caravans.
- Trailers designed to be hauled in an 18-wheel tractor-trailer configuration, which come in many configurations:
- * Roll trailer, Flat bed or open trailers, which are platforms with no sides or stakes. This type of trailer works well for hauling large or unconventional shaped objects. Some are small enough to be towed behind cars.
- * Tank trailers, which are trailers designed to contain liquids such as milk, water or motor fuel.
- * Container trailers are standard intermodal "boxes" that can be fitted with a dolly and front stand; they can then be used in a standard tractor-trailer combination. The containers are also stacked on ships and used as railroad boxcars.
- * Non-containerized tractor-trailer boxes are also fairly common, and work much like containers, above, but frequently with the stand and dolly integrated permanently into the box.
- Trailers for speciality applications that may require a specialized vehicle, such as a farm tractor; military truck, tank, or personnel carrier; or an unusually large semi-truck. Unpowered train cars pulled behind a locomotive can also be considered in this category.
- Hydraulic modular trailer, a special platform trailer unit which feature swing axles, hydraulic suspension, independently steerable axles, two or more axle rows, compatible to join two or more units longitudinally and laterally and uses power pack unit to steer and adjust height.
Towing safety
According to the United States National Highway Traffic Safety Association, more than 65,000 crashes involving passenger vehicles towing trailers occurred in 2004 in the US, increasing nearly 20 percent from the previous year.
In 2006, Master Lock did their annual study on towing safety to see how many Americans tow their cargo correctly. The study, Towing Troubles included responses from trailer owners across the country and found that while the majority of trailer owners believe they know what they are doing when it comes to towing, most were lacking the proper education. Master Lock reported that 70 percent of trailer owners did not fully know the correct way to tow their cargo.
An important factor in towing safety is 'tongue weight', the weight with which the trailer presses down on the tow vehicle's hitch. Insufficient tongue weight can cause the trailer to sway back and forth when towed. Too much tongue weight can cause problems with the tow vehicle.
Towbar wiring
Vehicle-specific
Of the many cars fitted with towbars, most are likely to have fitted towing electrics which are 'hidden' from the car.Since the early 2000s, vehicle technology advancements have introduced CAN bus network systems which allowed the interaction of different systems, and also the detection of a trailer or caravan. In some cases, the manufacturers have not only designed automobiles to sense the presence of a trailer, but they have also added enhanced new features within the systems connected to the network. This actually makes it important that these particular vehicles can "see" the trailer or caravan. A few of these new features are for safety and stability, but most are merely convenience features, such as automatically switching off the rear fog light and parking sensors.
The main new safety feature, appearing now on some cars, is the trailer stability program, which automatically turns on when a trailer is detected in the network through the dedicated sensors. These systems can detect the "snaking" of a trailer or caravan and counteract it by braking individual wheels, reducing engine torque and slowing the vehicle down. Activation of TSP normally requires a vehicle-specific wiring loom to be installed.
Some of the advanced systems being introduced in certain vehicles, which may make use of detecting the presence of a trailer, are: lane-change assistant, brake electronics, adaptive cruise control, suspension system, engine electronics, engine cooling system, parking aids, and reversing camera.
Some suspension systems can now detect a trailer and allow for a more level towing adjustment when the load is applied on the towing hitch. ACC systems are meant to 'detect' a trailer to allow for a greater braking distance between vehicles. Bypassing such vehicles' trailer detection systems may cause problems, as these vehicles may be designed to behave in a different way when a trailer is attached.
Some manufacturers either put a prepared connector in the vehicle which is a preparation on the network to accept a specially designed towing module, or have designed the trailer to be 'detected' through connections directly onto the databus. With such connections the vehicle will know when a trailer plug is connected to the socket.
On vehicles that do not have safety features that depend on the vehicle sensing the presence of a trailer, bypass systems, properly installed by expert fitters, are very efficient and cost-effective alternatives to expensive OEM and other dedicated kits. All bypass kits will be type approved for use on vehicles. They have the built-in advantage of completely isolating the trailer from the vehicle's lighting system, thus protecting against damage to the car caused by any failure within the trailer's wiring. However, a number of manufacturers do not recommend connections to be made on the lighting harnesses.
Universal by-pass electronics
This system is used to protect the car's lighting systems from potential damage if wiring in a trailer should malfunction. Such installations are in very wide use. Bypass systems are found both in "universal" systems and in dedicated and OEM systems. It works by taking a small current signal from the vehicle's lighting harness to trigger a relay and send a direct power supply to the towing socket. It does not communicate with the vehicle and will not activate any safety or convenience systems. It has the built-in advantage of isolating the trailer wiring from that of the towing vehicle and thus preventing overloading the vehicle's own lighting harness which may be minimal gauge cabling. The connection onto this harness will cause damage if solder or crimp connectors are used. However, by-pass systems should protect the car's electrical modules from damage should the wiring in a towed trailer malfunction. It is not advised for use in cars that depend on sensing the presence of a trailer to activate towing-related safety features within the car. In addition to this, there are a number of vehicle manufacturers that do not recommend or actually ban any connections to be made from the vehicle lighting harness.12N, 12S or 13-pin sockets
12N is the designation for the older 7-pin lighting socket conforming to ISO 1724, used when towing just a trailer or caravan. In the United Kingdom, it has all the functions of the rear lights on a vehicle except for reverse. These sockets are not waterproof and suffer from "pin burn-out" when worn.12S is an additional 7-pin socket conforming to ISO 3732, mainly used when towing caravans. It consists of a permanent 12 V power supply, and usually a switched 12 V power supply for the fridge. It also contains a feed for the reverse lights on the caravan.
ISO 11446 is the 13-pin standard socket being fitted for all new UK caravans and trailers sold from 2009 onwards. It can be wired with the same functions as both the 12N and 12S sockets, or with just the lighting functions including reverse. The socket has been designed to be waterproof, easy to fit and remove, the same size as one 12N socket, and with good fitting quality terminals that avoid any pin burnout or voltage failure.