Few people know it ~ and shame on them ~ but trailers designed for shipping containers are telescopic. Incidentally in the US they are called semi-trailers, on the pretext that they are not self-supporting without a truck tucked underneath at the forward end. I view that as a technicality, but it’s not worth falling out over.
We enjoyed a recent discussion of container sizes, didn’t we, over in Trafford? Well now if you’d like to take out your exercise books we’ll discuss why such trailers ~ called sliders or skeletons in the trade ~ can be shrunk or extended at will. If we forget about 30-foot containers, which most people seem too have done anyway, stock 20-foot and 40-foot boxes have a socket for a twist-lock at each corner to hold them in place on ships, trucks and trains. In Cuba they are used as houses as I write, and I guess you could use each of these points to pin them to the ground with the hurricane season in view?
With the 20-foot soon extended to 40-foot incidentally it was perhaps inevitable that we would want something larger again, but the constraints involved in manoeuvring anything much larger given existing infrastructure would mean limiting this extension to five feet. The 45-foot container however was created by leaving the anchor-points as they were and adding a 2’6” extension at either end. Driving this takes a little forethought as it produces an out-swing at the rear during turns and much the same at the forward end; where for instance it might catch a gate-post during turns at a sharp angle.
Broadly speaking then the trailer is run extended and has attachments in the middle for 20-foot containers and at each corner for the 40-foot. The trailer has then to be shrunk in order to allow access to the rear doors of the shorter boxes. A minor point too is that it can also be shortened by around eight inches in order to shift the centre of gravity of the longer 45-foot containers forward a little, principally to satisfy the requirements of the anti-skid system fitted to the trailer.
This Westinghouse type of braking system is powered by the pneumatic lines from the tractor-unit, and if disconnected from it the brakes will normally be applied automatically in order to stop the trailer rolling away upon disconnection… although the extendable legs do prevent this to a large extent. There is also a manual plunger to release the trailer’s brakes before the get-go, and if the trailer is unladen and the surface wet, the truck will happily drag it down the road with the driver largely unaware: one reason for leaving the window open at the off in order to clock the squealing.
It is also a reason for not bouncing to tunes on the radio until established, because the first thing to alert you to anything amiss is generally accompanied by an audible tell-tale. For this reason I was not a fan of noise-cancelling headsets in airliners, and invariably flew with one ear exposed so as to able to chat with the co-pilot. It meant however that you were able to listen to the hum of those jet-engines like a parent the gentle breathing of a sleeping baby: those CFM-56s being yours.
