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ilif ith skeletals, weight is less of an issue than chassis strength and reliability. 'While some manufacturers have tried to get as close to 4.0 tonnes as they can in recent years, the majority settle at around 4.5 tonnes, and the market seems happy with that,' says Trevor Chapman, product manager skeletals, at Fruehauf. "t gives you enough capacity to carry a 30tonne container on a 44-tonner."
Even higher trailer weights seem to be accepted by many operators. Dennison's latest all-steel sliding skeletal tips the scales at 4.7 tonnes—atthough clever use of aluminium components can bring this down to 4.5 tonnes.
Montracon's is a no-nonsense 5.0tonnes or thereabouts, with disc brakes and EBS fitted as standard.
A sliding skeletal exhibited by SDC at the recent Commercial Vehicle Show weighed 4.4 tonnes, thanks to the extensive use of high tensile steel—a material favoured by a number of manufacturers.
"We use medium-high tensile, but not ultra-high tensile," says Chapman. "If you employ the latter you'll use less material, but the trailer will suffer excessively from deflection." Close attention to detail is required to ensure that a slid ing skeletal operates efficiently. "Sliders account for about BO% of the market, and operators want to be able to slide them under all conditions," he comments.
Fruehauf uses large-diameter rollers with the aim of making the top frame slide on the lower frame with minimal effort. The bottom frame has a thick, smooth, stainless steel top flange to ease their passage.
Independent
Each roller has an independent phosphor-bronze grease-fed bearing for smooth rolling, and the greasing points are easily accessible.
Durability is also a concern. The twistlock spindles on Fruehauf's sliding skeletals, for example, are chromed zinccoated to prevent corrosion, and can be removed quickly if damaged.
The bump bar is galvanised, and the entire chassis can receive the same
treatment for an extra £400, but it also adds 90kg to the weight. "Container ports are by the sea, so the air tends to be salty, and galvanising the chassis helps pro
tect the trailer from corrosion," Chapman explains.
Versatility is a further consideration. With a lighter rear bolster, a deeper rear chassis beam, and an all-bolted mud wing, the most recent version of Dennison's sliding skeletal can accommodate 45ft as well as 20ft, 30ft, 40ft, and 13.6m containers.
Extra twist locks—a total of 14 are fitted—have been mounted 150mm ahead of the front bolster to accommodate 45ft boxes without affecting the trailer's forward-swing clearance, says the company.
"Remember that the distance from the kingpin to the rear of the vehicle must not exceed 12m, so there can sometimes be a problem with the longest containers fouling the back of the tractor's cab unless they have chamfered front corners," says Chapman.
"In those circumstances, you also need a front coupling frame that pulls out so that the tractor and trailer couplings don't end up under the front of the container."
Fruehauf's trailers come with a pullout rear bump bar as a standard fitment. This is required when boxes more than 40ft long have to be carried. Skeietals can be fitted with a front-lift axle on the rear bogie to aid traction on slippery surfaces. Raise it, and weight is transferred to the tractive unit's drive axle so that the vehicle can move away from rest without the wheels spinning helplessly.
Keep running with it raised, however, and it's likely that you'll infringe the turning circle regulations because, by doing so, you're extending the wheelbase. You may also end up overloading the rest of the vehicle's axles.
"That's why we fit a device that lowers the lift axle automatically at 15km/h," says Chapman.
While fixed-length skeletals account for a minority of sales, they're still favoured by some operators. Dennison's are now available with an optional double-front bolster arrangement based on a requirement from Roadways that allows boxes up to 45ft long to be carried legally. in common with some of its competitors, it also makes platform and tipping skeletals plus a range of skeletal tank carriers.
There's no denying that there's plenty of demand for skeletals, "It's a buoyant market, and we're building them in substantial numbers for Colease in particular," says Ron Steel, sales manager at M&G Trailers.
Dennison has received orders for its sliding skeletal from Colease, Magnus Logistics, and Goldstar among others, but the biggest single order it has won this year—for 112—was paced by Transrent.
Specialised trombone trailers equipped with a Swing Thru system by King Trailers (so that they can load and unload containers without assistance) sell in far lower numbers. Developed in New Zealand, Swing Thru uses a pair of hydraulically-powered cranes to Litt boxes up to 45ft in length and weighing up to 35 tonnes. Its stabilising legs allow it to operate on uneven, non-reinforced surfaces, and it can stack containers weighing up to 28 tonnes two high.
It can lead and unload containers from either side of the trailer, put them on the ground, and pick them up again. It can also lift a container off a rail wagon and drop it onto the trailer, and vice versa. And the price of the whole package? Around 1.130,000.
However, if you can't stretch to investing in overhead lifting tackle, other ways of loading and unloading boxes are also available.
Stack 'ern
Manitou makes a range of masted and telescopic boom lift trucks that can cope with containers weighing up to 16 tonnes, while Kalmar's reachstackers can lift boxes weighing up to 45 tonnes and stack them six high.
Such equipment doesn't come cheap, however. Kalmar's machines will set you back up to £290,000, and you may have to strengthen your yard's surface before you can use them.
Kalmar also makes lower-capacity reachstackers and mast-type lift trucks that can be used to stack empty containers. With containers travelling all over the world, wilily is a daily concern.
Desperate illegal immigrants may occasionally attempt to enter the UK in containers. "it's very rare that this happens, however, and the consequences for anybody who tries it can be disastrous, because they're virtually air-tight," says Frank Heinrich-Jones, director of transport security at PLC Consultancy Services.
In a tragic incident, eight stowaways perished inside a container delivered to Waterford Port in the Irish Republic in December 2001.
Some ports have since installed technology to detect a human presence inside containers, such as heartbeat detectors.
"Part of the load may be stolen and replaced with something of equal weight, and nobody can be sure at what point during the journey the theft occurred," says Heinrich-Jones. "Entire containers and their contents can sometimes disappear, and although tracking systems are available, shippers may take the view that the cost of installing them is prohibitive."
He strongly advises hauliers to check the seals on the doors of any container they're asked to pick up, and ensure that the number on the seal matches the number on the paperwork.
Security clamps can be fitted to the rear doors for around £40 to 2,45 each. "Shipping lines are starting to insist on them, but if you're going to use them, then you must fit them to every single container," says Road Haulage Association security committee chairman, Tony Allen.
"If you only fit them to those containing valuable cargo, then all you're doing is giving thieves a signal that they hold something that's worth stealing."