Synthetic rope fibres
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Although traditionally scouts use natural fibre ropes for pioneering projects, synthetic fibre ropes are becoming cheaper and easily available from the local hardware shop.
To use the best rope for the job we need to understand the fibres the rope is made from:
- Nylon (Specific gravity = 1.14). Good UV resistance. Does not absorb water (Nylon is hygroscopic and is 10–15% weaker when wet) Melts at 256°C. Has 40% stretch at break. Nylon is weakened by strong acids and cannot be used in contact with the electrolyte used in lead–acid batteries.
- Polyester - (Specific gravity = 1.38). Good UV resistance. Does not absorb water. Resistant to acids and alkali. Stretches 30% at break - less stretch than nylon. White Polyester is stronger than coloured Polyester. Melts at 255°C.
- Polyethylene - has a specific gravity of 0.91-0.94. Relative low strength. UV resistance is good. Used for ski ropes. Has 65% stretch at break. Melts at 120°C.
- Polypropylene - used in lower quality ropes. (Specific gravity = 0.855). Melts at 160°C.
- Ultra High Molecular Weight Polyethylene (UHMWPE) (Specific gravity = 0.97). Is a type of the thermoplastic polyethylene. It has a very low stretch 2-5% at break. Melts at 147°C.
- Vectran has no or very little stretch. It is sensitive to sunlight with poor UV stability. (Specific gravity = 1.45). Stretch at break is 2.4%. Melts at 400°C
- Kevlar is a lightweight, high strength fibre which is cut and heat resistant (Specific gravity = 1.44). It is not UV resistant. Melts at ~430 °C
Note:
Water has a specific gravity (S.G.) of about 0.9998.
- A rope with a lower SG will float in water.
- A rope with a higher SG will sink in water.