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ish Ropes Securing devices
Page 81
Page 82
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IN a recent letter to the editor of a daily newspaper the writer complained about the "appalling condition of the load-securing methods used by the majority of haulage concerns". He found it strange that in this technological age loads were still being secured by a system that was surely devised in the day of the horse and cart.
To the uninitiated the use of an unsophisticated method spells inefficiency. But is such a system really outdated? Just what are the pros and cons of using the oldfashioned rope method as compared with some of the supposedly more desirable ways of ensuring that a load does not shift while in transit?
To find the answers I recently spent a day at the Greenwich works of British Ropes Ltd., and carried out a number of tests on three types of rope; one was on the most commonly used lorry rope, 1.5in. circumference sisal, the others on two manufactured from man-made fibres and film. I discussed with British Ropes the many other load-securing materials which it produces and I left the works with the impression that no matter what sort of load it is necessary to tie on to a lorry, this firm will provide the correct equipment for the job.
Apart from its manufacture of rope, British Ropes weave a wide variety of nylon and Terylene webbings which it will sew into the most intricate harnesses for use on the own-account operator's regular-shaped traffic. I make this point because the general haulier or sub-contractor cannot, of course, take advantage of this type of harness unless he knows that every load he handles will measure Xft by Xft. However, webbing can be produced in substantial straps with rope ends and lashing eyes which enable their use on diverse loads.
Man-made fibres, when woven or twisted into a given size of lashing, whether rope or strap, are just about twice as strong as natural fibres. They have the added advantages that they will not rot, are impervious to oils and greases and remain easily handled when saturated with water.
Every transport man who is any good knows the basic method of lashing cargo aboard a flat or low-sided lorry. It is an age-old method, one which if properly carried out will secure the most awkward loads adequately no matter what conditions of ride are endured. In fact when a vehicle does tip over, provided its load has been roped by an expert it will often remain securely fastened to the vehicle to such an extent that more damage is done to the cargo when the ropes are cut to free the load than occurred during the actual turnover. Unfortunately this state of affairs pre-. vails only when the ropes and the points to which they are fastened to the body of the vehicle are in good condition.
Tests carried out by a major C-licence firm recently, showed that the average life of a natural-fibre rope was approximately two months. Its vehicles carry seven ropes per unit and the cost of 42 hanks per vehicle per year was becoming prohibitive. A more surprising fact arising from the investigadon, in my opinion, was that ropes became generally unserviceable in a period as short as two months.
Ministry of Transport efforts to ensure that commercial vehicles are kept in good repair can mean little if the loads carried are—unknown to the driver—unsafe because the load-securing ropes are of insufficient strength.
During my visit I tested three types of rope on a tension-testing bench. Because a rope should never be tensioned around a diameter less than five times its own circumference, I had imagined that the point of break would definitely occur at the tying hook. In fact every rope tested, no matter what its condition or the type of dolly put in it, snapped at the first loop of the dolly. New ropes snapped at a little over half their rated loading while old rope, which had seen considerable service, snapped at 0.4 of its rated load.
With the natural-fibre rope soaked with water, I was able to see exactly how much shrinkage had taken place. This highlighted the reason for the bone-hard knots I have spent ages trying to release at the end of a long run in heavy rain. New sisal rope had shrunk some 5 per cent after prolonged soaking and this also explains why loads tied down in the rain can shift so easily once the weather clears up.
The generally used lorry rope is 1.5in. circumference sisal. It has a load rating of 1 ton but on the three tests ,carried out when the rope was dry, the following results were obtained: Tied with a safety dolly, that is to say with a double-turn round the loop and with the sliding loop twisted, it snapped two strands at 0.62 tons. With a standard dolly, one turn on the loop and the slider twisted, it broke one strand at 0.575 tons. A single untwisted dolly broke at 0.5 tons. In each case the break was in exactly the same place and at no time was there any sign that the dolly would slip.
A straight pull with the rope turned round a 0.5in. diameter pin caused a break, again one strand, to occur at 0.86 tons, while a similar test around a 2in. diameter pin produced a figure of 1.265 tons. I then tied the rope off in a reef knot taking it round a 2in. pin at each end of the loop; it broke at 1.63 tons.
These tests showed that basically the rope is adequately strong, but that the use of the time-honoured dolly produces a weak point. The man-made fibre rapes tested broke in precisely the same place and also produced just about half their rated capacity. When the old rope was tested it was significant, in my view, that this was the only time that the dolly knot slipped—yet another reason to discard worn ropes.
To find out just what sort of strain a driver puts on his ropes when he is pulling a load down, we rigged a rope into a test balance and I made a dolly and pulled it down. Despite the fact that the free end of the rope was a bit on the low side, I managed to raise the register to 2751b and jerk it to 3001b. Had I been able to apply the correct amount of purchase to the rope, I am confident I could have pulled 350Ib which would have certainly broken the old rope used in the tests.
The use of webbing straps provides the ' added advantage of load protection. A small diameter rope pulled down hard on to lightweight packing materials—cardboard boxes and the like— will do untold damage. But a strap imposes its load over a much larger area and will hold securely without damage.
For companies carrying materials which cannot readily be secured by rope or straps, a further section of the British Ropes group of companies, Edge and Sons Ltd. of Shifnal, Shropshire, manufactures a wide range of chains and load binders.
The lesson I learned during my visit is that load securing is not a subject upon which hard and fast rules apply. One must take the fullest advantage of the service offered by the manufacturer to assess the suitability or otherwise of his chosen method and then be prepared to change to the horse that best suits the course.
Technical information about any loadsecuring problem can be obtained from British Ropes Ltd., Anchor and Hope Lane, Greenwich, London, SE7.