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howdown on loads
Page 52
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ANAGED to work a load to Glasgow during the ttish Motor Show and, ng a few hours to wait for return load, I popped g to Kelvin Hall. '
;aw some fantastically intriand well-executed paint It's a sad fact that most of ese days go in for straightrd colour schemes with 'Hy uninteresting sign1g, but there were several good examples on show of ■ tyles that used to grace e a big fleet in days gone 'ere were also a couple of y dangerous examples of security exhibited, by e who should know better, e demonstration park.
ro vehicles were ballasted blocks of concrete ling about 2 tons apiece, urely held on with what I inly describe as "string". the method of roping was ucated. The passes over ocks did less than no good. )ne of the vehicles had to luickly or change direction anly, the ballast would simply carried on along its al line of travel. To make )rs worse, the Scottish ler had nicely soaked the )oards, making them very ry and, to round off the rs of the whole shebang, ornings were offering the November frosts.
iat should be done with a load? If it's necessary se of its density to spread dividual parts of that load er to obtain correct load ution, the first essential is vent any initial movement load units.
hings will not do the job s they are of noniable material, such as or steel bonds. Even then use simply passing the js over the unit from side . They must be applied so bsorb the stresses applied y possible movement, lh their tensile strength. igure 1.) s look at what we are ing if we simply pass rope is over the top of a load unit. The sums are simple.
Say the load unit weighs 1 ton. If the coefficient of friction between the load unit and the vehicle floor is 0.8, a longitudinal force of 1 6cwt will cause it to slide along the floor. With a wet floor, the coefficient will be more like 0.5 and so with the vehicle braking at 0.25g and cornering at 0.25g the load will slide.
We improve the situation only slightly by the downward force we apply through our lashings.
Let's say we are using a normal single "driver's dolly" method of pulling down; this will give us a purchase of two to one on the rope. If the driver weighs 200lb and we are suffering a 25 per cent loss due to the friction in the dolly and around the rope-hook, that allows us to put a downward force on our load unit of 1 501b. for each lashing we put over it.
So four lashings would in crease the pressure on the deck by the load to the tune of 600Ib or 5.35cwt.
If we take our 0.5 coefficient of friction the worth of our roping is in fact only 2.67cwt or 13.35 of the 1 ton weight. The rope makes no other contribution towards restraining the load unit because the force applied to it by the load unit moving is not a tensile force, but rather a bending force against which a rope has virtually no resistance. The extra longitudinal force needed to slide our roped down block is only 2.67cwt.
The safest method of securing sucli a load is to block it with substantial timbers and to bolt these through the deck. ' Alternatively, start the load or the blocking right tight up on 1 the headboard so as to prevent any initial movement taking place.
We reproduce a picture taken at MIRA during a CM road test some years ago when a test load got away.
If you cannot use a blocking system, insist on using chains, with tensioners either of the over-centre lever type or with screw bottles on them. And when you apply them, use your brain and work out a Sensible pattern of lashing.