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| 75mm |
Ropes come in many types and sizes and to simplify matters you should use the following as a guide.
- 75mm rope (25 mm diameter) or larger, certainly no smaller than 75mm, should be used whenever it is intended to hold weight such as in the case of a monkey bridge - foot and hand rails, aerial runways, and commando rope bridges.
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50 mm
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- 50 mm rope (16 mm diameter) should be used for ‘reeving’ up pulleysand anchors and for rope ladders.
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| 25mm |
- 25mm rope (8mm diametere) should be used for guy ropes in general, on large structures this size would need to be increased.
Rope lenghts will vary according to how they are purchased, 25 metre lenghts will normally cover most projects as the distance between sheer legs or rope bridges should not exceed 15 metres to avoid ‘flipover’. Flipover occurs when the slack in the rope is such that it acts much like a skipping rope, when pressure is applied to the middle of the rope it becomes unstable and sways resulting in throwing off the ‘rope crosser’ or entangling them in the ropes, which is extremely dangerous. As most of the ropes used in pioneering structures require an element of friction to provide maximum efficiency, hawser laid ropes of natural fibre such as sisal or hemp are preferred, but they are more expensive and need care and attention as the fibres can rot and deteriorate if not dried carefully. Synthetic ropes are cheap but require extra care particularly when fixing the ropes to trees and poles. The ropes are generally smoother than hemp or sisal ropes and the knots have a tendency to slip under pressure. To ensure safety and prevent slippage you should secure all knots with extra hitches.