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Fibre rope and slings
Construction of fibre rope
Find out how fibre ropes are constructed and what materials they are made from.
Fibre ropes can be made from either natural or synthetic materials, but synthetic ropes are preferred due to their resistance to moisture and UV degradation.
Synthetic ropes can be used for lifting, winching and hand lines.
How do natural and synthetic fibre ropes compare?
| Generic fibre type | High module polyethylene (HMPE) | Nylon | Polypropylene | Polyethylene |
|---|---|---|---|---|
| Tenacity (G/DEN) | 40 | 7.5 - 10.5 | 6.5 | – |
| Elongation | 3.6% | 15 - 28% | 18 - 22% | 23 - 26% |
| Coefficient of friction (resistance to slipping) | 0.05 - 0.07 (very low) | 0.12 - 0.15 (medium) | 0.15 - 0.22 (medium) | – |
| Melting point | 149°C | 218-254°C | 166°C | 135°C |
| Critical temperature (degradation caused by temperature) | 65.5°C | 163°C | 121°C | 80°C |
| Specific gravity | Floats | Sinks | Floats | Floats |
| Application | Yachting, towing, winches, marine, rigging and specific lifting applications | Towing straps, anchor lines for small boats | General purpose tying, fishing, water ski ropes | General industrial, marine |
| Advantages | High strength to weight ratio, UV stable, high abrasion resistance, low stretch | Good UV and abrasion resistance, rot and mildew resistance | Floats, inert when exposed to chemicals, resists rot and mildew and UV resistance | Excellent handling properties, superior splicing efficiency in medium and soft lay |
| Disadvantages | Low melting point, low coefficient of friction - results in less gripping | Sinks, loses strength when wet, not suitable for uses which require dimensional stability like rigging, degrades in high heat | Lower strength, sensitive to UV degradation, slippery (knots can come undone). Not recommended where rope is subjected to high stresses | Low melting point, higher stretch |
Table: Synthetic rope comparison chart
Natural fibre types
Sisal rope
The properties of Sisal rope include:
- Individual fibres are shorter than Manila and prone to splintering.
- Excellent resistance to sunlight.
- 'Hair finish' makes them excellent for use where grip is important.
- Little or no stretch.
- Must be stored in dry conditions to prevent mildew.
- Available in 4 to 24mm diameter sizes.
- Used in tag lines for riggers and general purpose non-lifting.
- Not to be used for lifting.
Sisal rope
Manila rope
Properties of Manila rope includes:
- Individual fibres are longer than Sisal.
- Has good strength to size ratio.
- Very good knot tying ability.
- Can be spliced easily and can withstand repeated wetting and drying cycles.
- Measured under tension during production so it might appear oversized before use.
- Highly resistant to salt water.
- Available in 6 to 24mm diameter sizes.
- Will shrink in length and expand in diameter when wet.
- Will lengthen as it dries.
- A wet knot will become tighter and less likely to slip, give way or untie.
- Used in tag lines, sailing and marine, children's playgrounds, gym ropes and barrier fencing ropes.
- Not to be used for lifting.
Manila rope
Synthetic fibre types
Synthetic ropes provide multiple benefits including being:
- lightweight
- flexible
- safe to use and handle.
Synthetic fibre ropes can be categorised into two types based on the fibres used:
- Class I - Polypropylene, Polyethylene,Nylon and Polyester.
The tenacities of the fibres are 15g/Denier
Total stretch at break is 6% - Class II - High Modulous Polyethylene (HMPE) (Dyneema)
The tenacities of the fibres are >15g/Denier
Total stretch at break 6%
Both Class I and Class II can be produced with the following varieties:
- 3 strand
- 8 strand
- 12 strand
- single braid
- double braid
- core dependant braid.
Synthetic rope
Strength
Strength is one of the most important considerations when choosing the right synthetic rope. There is a lot of variation in fibres resulting in different strengths.
Most synthetic fibres have negligible water absorption. However, nylon fibres can lose up to 20% of their strength when wet. When a rope strength or minimum breaking load is referenced, it will always refer to the dry and un-spliced condition.
The working capacity of a rope together with the safety factors determine the choice of a synthetic fibre rope. In general working capacity: minimum breaking load (MBL) divided by the safety factor.
Working capacity does not take into consideration shock loading or dynamic loading. For example, sudden drops, snubs or long term sustained loads.
A higher safety factor in these situations should be considered.
How are fibre ropes made?
This video shows the rope making process from raw, synthetic materials to slings.
Fibre rope making process
Natural fibres such as sisal or manila are often used in tag lines for maintaining control of loads at safe distance.
Note: fibre rope tag lines should not be less than 16mm in diameter.
Here are some typical rope constructions:
Typical fibre rope constructions