AT THE HEART OF THE ROAD TRANSPORT INDUSTRY.

Call our Sales Team on 0208 912 2120

Supercube semi-trailer equals drawbar capacity

13th February 1982
Page 40
Page 41
Page 42
Page 40, 13th February 1982 — Supercube semi-trailer equals drawbar capacity
Close
Noticed an error?
If you've noticed an error in this article please click here to report it so we can fix it.

Which of the following most accurately describes the problem?

While Silentnight claims that its new Vanplan-based Optimised Trailer has the largest cube in the UK, is it viable? David Wilcox investigates

TRAILER 96 in the Silentnight fleet is unique. Although to the casual observer it does not look wildly different from anything else on the road, it nevertheless lays claim to the record of the largest cube of any semi-trailer in Britain.

I had visited bed manufacturer Silentnight at its factory in Barnoldswick last spring to talk about its very impressive new drawbar outfits (CM April 11, 1981.) Before that the company had operated a mixture of 11.3m (37ft) artic box trailers and Bedford TK rigids with 9.1m (30ft) box bodies. In their search for maximum cubic capacity in their vehicles, the men at Silentnight had turned to drawbars and when I saw them they had six Dodge G13-based outfits each with two 7.3m (24ft) demountable boxes.

Silentnight's transport and distribution manager, Fred Short, told me then that the company had not definitely decided to go down the drawbar path — the outfits were to be on trial for nine months or so. And in addition to the drawbars, Silentnight had something else up its sleeve — trailer 96. This was due for delivery in May last year, about a month after my visit, christened the Optimised Trailer.

Silentnight intended to operate this super-cube unit, alongside the drawbars, he said, and the rest of the fleet and see how it compared.

Before looking at the success (or otherwise) of the Optimised Trailer, Fred Short explained how it was developed and what makes it special. Its design was from a consortium of ideas by Silentnight's own engineers, trailer manufacturer Primrose of Blackburn, bodybuilder Vanplan and Loughborough University lecturer Philip Wilson, who was acting as a consultant to Silentnight.

"We started out by saying that the trailer had to offer a cube of no less than that of thE drawbars. That was our desior parameter," explained Fred.

At first glance that seems E near impossible rationale. Wit

their two 7.3m (24ft) bodies anc minimum deck height, Silent.

night's drawbars are alread) cavernous, offering almos• 105cum (3,700cuft) of cube. Hovr can a conventional semi-trail& compete with this? A common or-garden 12.2m (40ft) semi trailer has a cube of arounc 76cum (2,650cuft).

Silentnight limited itself to ar overall height of 4.1m (13ft 6in) which is the same as that of thE drawbars and the maximir practical figure bearing in minc that the driver has to get to the top of the load.

Although semi-trailer length not (so far) limited by law, thE restriction on artic length to 15rr effectively decided this dimen sion. By reducing the cab/traile clearance to a minimum, the de sign team came up with a semi trailer that is 12.7m (41ft 6in long and toes the line at exact!) 15m when coupled up to thE unit.

Width is of course restricted tr

I which means that the only r dimension that can be ed is deck height. To get this n as low as possible Primdesigned a stepframe semiir using a shallower-than'al chassis, although being 'ul to bolster other mea'rents to retain adequate igth.

her space-saving dodges on chassis include the use of beam axles and the cunning in which the tubular crossibers double as the air 5. Ground clearance was re to 25cm (10in), which was 3west they dare go.

e result of these techniques to produce a deck height of $6cm (Thin) which allows a ;ive 3,66m (12ft) of internal it. This is primarily where Optimised Trailer scores the already good drawbars h have an internal height of Ater 2.6m (9ft 6in). Even the end of the Optimised 3r over the stepframe has ternal height of 2.74m (9ft).

ternally, the Vanplan body a bow front to allow for swing on corners and to a slight aerodynamic effect. ton body style was considbut rejected, partly because cessive trailer swing on cor cess is mainly via a fullh rear roller shutter and -down tailboard. A hinged door is fitted on both sides e semi-trailer because of the ber of one-way streets that dictate unloading on a particular side.

Once you step inside trailer 96 its vastness seems almost overwhelming. "Silentnight is holding its annual dance in there," said someone, To save a couple of inches on the internal width, the usual tie rails have been omitted and the straps hang from the roof and are secured in a slotted track in the floor.

While saving space, this arrangement left the driver with a

problem since he uses the tie rails to clamber up and reach the top of the load. So, instead, trailer 96 incorporates a cunning fold-away aluminium ladder that runs along a narrow runner at the nearside top of the body.

Driver feedback has not been too complimentary about this combination of strapping and ladder and so for future examples of the Optimised Trailer Silentnight would retain the conventional tie rails and sacrifice a tiny amount of cube.

Because the semi-trailer has a tandem axle with single wheels, the wheelboxes do not intrude too far into the floor space. The clearance within the wheelboxes has also been reduced to a minimum. The logical extension to this cube maximisation policy would be to incorporate air suspension to eliminate spring deflection and so enable even less wheelbox clearance, but Silentnight did not choose to go this far.

Another bedding manufacturer within the Silentnight group has a similar (but shorter) version of the Optimised Trailer and has opted for air suspension.

The Optimised Trailer does achieve the objective that Silentnight was aiming for; it has a cube of 105cum (3,700cuft), the same as the company's drawbars.

To pull the Optimised Trailer, Silentnight uses a Ford D2817 tractive unit. The gross weight of the complete outfit is about 16 tons (which includes a payload of five or six tons) but the company chose a D-Series unit rated at 28 tons gcw in view of the terrific air drag of such a large semi-trailer.

The same unit has been kept with the trailer throughout its nine months of operation because the unit's fifth-wheel position had to be moved rearwards to give sufficient trailer swing clearance. As it is, the clearance is still noticeably small and even the susies had to be mounted hi gh up on the semi-trailer front to avoid the flexible lines getting tangled.

So that's the semi-trailer's specification. But how does it work in practice? In the nine months it has been on the road, trailer 96 has been used fairly intensively and has averaged 1,100 miles a week compared with the 840 miles a week average for the 11.3m (37ft) semitrailers in the Silentnight fleet.

Fred Short said that its regular driver has reported no special problems with it, apart from the lack of tie rails already mentioned. I wondered if such a large, slab-sided semi-trailer is rather susceptible to side winds, but apparently this is not the case. Because the trailer is so close to the ground, it is less topheavy and side winds do not get underneath it to the same extent. The use of a tandem axle rather than a single axle is also said to improve stability.

The minimal ground clearance has not caused problems so far but the driver has to remember that there are only 10 inches between the trailer and the ground.

Fuel consumption for the Optimised Trailer outfit is not so significantly different from that of the drawbars to be able to draw any firm conclusions. It has averaged 31.38 lit/100km (9mpg) while the drawbars are recording 33.23 lit/1 00km (8.5mpg) on average.

Because of its size the Optimised Trailer is naturally a little unwieldy and so Silentnight's traffic office is careful where it sends it. The company's deliveries fall into two categories: to stores and furniture discount warehouses; and in the case of beds bought through mail order catalogues, direct to people's houses. Said Fred Short: "We obviously can't send the Optimised Trailer out on deliveries to private addresses on housing estates.

"We first tried it on our usual multi-drop shop deliveries doing about seven drops per journey. Then we switched it to routes involving fewer but larger drops and now we use it for the largest bulk deliveries such as department stores and warehouses where there are just one, two or three drops on the journey."

In certain circumstances the Optimised Trailer can prove more efficient than a drawbar outfit, even on multi-drop work. For instance, if Silentnight has six deliveries to make aroud London, a drawbar outfit would probably trunk down from Barnoldswick, leave the trailer at a focal point in London and make the first three deliveries as a rigid. It would then return empty to the focal point, swop demount boxes, make the remaining three deliveries and return to the focal point to pick up the trailer for the journey back to Barnoldswick.

The Optimised Trailer is capable of carrying the same-size load but could make the six deliveries on a conventional circular route, eliminating the drawbar's time and dead mileage involved in returning to the focal point to swop demount boxes.

Fred Short summed it up when he said: "The Optimised Trailer is a specialised animal whereas the drawbars are versatile. The trailer needs careful route selection, but under the right circumstances it can prove very cost effective."

How cost effective? It's all very well designing and producing the largest cube trailer, but how often is the extra cube really used? Fred Short was quickly able to demonstrate that trailer 96 is earning its keep.

Silentnight estimates that owing to minor intrusions such as wheelboxes and tie rails, plus odd inches wasted here and there, the actual maximum usable cube in a vehicle is 18 per cent less than the body's theoretical cube.

So this means that the realistic usable cube of the drawbars and of of the Optimised Trailer is about 86cum (3,035cuft), which compares with about 62cum (2,180cuft) in Silentnight's 37ft trailers.

The company can work out how much of this space is actually used by means of its computer; each of the company's products has a known cube and as the load is made up the computer totals the cube on each order.

Using this information Fred Short confirmed that the drawbars have been consistently operating at 79cum — 85cum (2,800cuft — 3,000cuft) while the Optimised Trailer has rarely dropped below 82cum (2,900cuft).

Is the Optimised Trailer worth the extra cost? When bought last spring the trailer alone cost £11,600 compared with £9,400 for Silentnight's 37ft trailers.

This means that in a straight comparison between the two types of semi-trailer the Optimised Trailer offers 39 per cent extra cube for 23 per cent extra initial price.

Comparing the Optimised Trailer with the drawbar outfits is not quite so straightforward. At spring 1981 prices (when Silentnight bought its first drawbar) the drawbar outfit complete with four demountable boxes cost £36,000. A fairer comparison would be to include only three of the boxes which brings the equivalent drawbar cost down to around £33,000.

The Optimised Trailer complete with its Ford D2817 unit cost £25,600. Silentnight reckons that the price of the Optimised Trailer (not including its unit) should be multiplied by 1.2 to compensate for the extra flexibility that the drawbars offer. This gives a computed price for the complete Optimised Trailer outfit of around £28,000 which compares for the similarly computed price of £33,000 for the equivalent cube drawbar. Which would seem to prove that the Optimised Trailer is cost effective.

Because of its fairl specialised nature, the Op, mised Trailer has a limited rol Fred Short said that the s drawbars in the fleet hal., proved themselves to be good as Silentnight had hope and another nine are in buil The plan is for the drawbar become the basic vehicle in th fleet and as the older rigic come up for renewal drawba will replace them.

But in addition to the e visaged "final" total of arour 70 drawbars, Fred also foresaw role for about five Optimist Trailers for those large bulk d liveries.

So trailer 96 is not destined become one of those one"freaks" that is never repeate Any operator with an equal strong desire for cube must s+ possibilities in a similar trailer.

One point to be borne in mui is that the Armitage Report pr posed an increase in overall ar length to 15.5m. But to ensu this meant that sleeper ca could be used legally and th the extra 0.5m was not mere added to the trailer, the Rept also proposed a limit on sen trailer length of 12.2m (40ft).

If Armitage is eventually ii plemented in full this wot, appear to rule out such monster as trailer 96, althoul the same techniques could applied to a 12.2m semi-trail with good effect.


comments powered by Disqus