Natural and synthetic fibre ropes and slings and are used in construction, painting, material handling, marine operations and transportation. Fiber ropes and slings are pliant, grip loads well, and do not mar the surface of the load. Information about rope construction, types of ropes and their properties is given in this article. The information will help in selection and use of a rope for an application. Ropes made from natural and synthetic material are also known as cordage.
Construction of Fiber Ropes
The most common constructions for fiber ropes are twisted / 3 strand laid, 8 strand plaited, and braided.
Twisted / 3 Strand Laid Ropes
Twisted ropes normally consisting of three strands which run over each other from left to right. The fibers within each of the three strands must twist in the opposite direction as the strands in order to produce a balanced rope, that is, one which hangs straight and resists kinking. Twisted rope must be taped / tied on each end to prevent untwisting of strands. Ends of synthetic ropes may be fused. Traditionally twisted ropes were made from natural fibres but nowadays they are made from synthetic materials.
Owing to their resilient nature, twisted ropes made from synthetic fibres show a tendency to twist / kink. To overcome this problem, ropes are made by plaiting and braiding.
8 Strand Plaited Ropes
In an 8 strand plaited construction, four left hand and four right hand strands are interlaced to give the rope a perfect balance.
Braided ropes
Braided ropes consist of a strong core of synthetic fibres covered by a braided sheath. In a double braid rope, inner core is of braided construction instead of fibres. Braided ropes are also made with out core. They are known as hollow braided ropes.
Types of Ropes
There are two types ropes as under based on type of fibre used for rope making.
Natural Fibre Ropes
They are made from natural materials like manila, sisal and coir. Natural fibre ropes are often referred to as real ropes or old-fashioned rope. These ropes are usually shades of brown. All natural fibre ropes, when used in a damp or wet environment, will eventually rot through. However the right rope for the job could last for 10 years. They are relatively cheap.
Synthetic Fibre Ropes
They are made from synthetic materials like nylon, polyester, polypropylene, etc. They are relatively expensive but last a long time. They are superior than natural fibre ropes because they are generally lighter, stronger, less prone to rot, water resistant and better able to withstand extreme environments.
Rope Materials
Manila
Manila is made of 3’ to 6’ long leaf fibers from the Abaca plant, a close relative of the Banana. The name refers to the capital of the Philippines, one of the main producers of Abaca It has good resistance to sunlight. It does not melt on contact with hot objects but will burn if the temperature is very high. It stretches very little under load. It deteriorates in presence of chemicals. It must be stored dry to avoid mildew. It is a good material for general outdoor use.
Sisal
Sisal is made of 2’ to 4’ long leaf fibers from the Agava Sisalana plant. It is very similar in texture to manila rope except that it is generally much lighter in colour. It’s properties are similar to manila but it is slightly weaker and cheaper than manila. It is not as good as manila for outdoor application.
Coir
Just like the coconut, from which it made, coir ropes will float. It is much lighter in weight as compared to manila. The larger sizes ropes are very stiff. They are used as fender for boats and tying bamboo for making scaffolding
Nylon
A polyamide is a polymer containing monomers of amides joined by peptide bonds. They can occur both naturally (e.g. proteins such as wool and silk) and artificially. Nylon is an artificially made polyamide. Nylon is the strongest of all ropes in common use. When stretched it has a "memory" for returning to its original length. For this reason it is best for absorbing shock loads. Nylon lasts 4-5 times longer than natural fibers because it has good abrasion resistance and is not damaged by oil or most chemicals. Like manila, nylon has good resistance to ultraviolet deterioration from sunlight.
Polyester
Polyester is very close to nylon in strength when a steady force is applied. However, unlike nylon, polyester stretches very little and therefore cannot absorb shock loads well. It is as resistant as nylon to moisture and chemicals, but is superior in resistance to abrasion and sunlight. Polyester is the most popular general purpose rope in the boating industry.
Polypropylene
Because of its light weight, polypropylene is the only rope which floats. For this reason, it is very popular for pool markers and water sports. It is affected by sunlight deterioration. It also begins to weaken and melt at 165°C, the lowest melting point of all synthetic ropes. It is not as strong as nylon or polyester, but is 2 times stronger than manila. Because it is less expensive than other fibers, it is the most popular rope for general application.
Comparison of various rope material characteristics is as under.
| Characteristics | Rating | Nylon | Polyester | Polypropylene | Manila |
|---|---|---|---|---|---|
| Strength | Strongest – 1 Weakest – 5 | 1 | 2 | 4 | 5 |
| Wet Strength vs. Dry Strength | – | 90% | 100% | 100% | 115% |
| Shock Load Ability | Strongest – 1 Weakest – 5 | 1 | 3 | 3 | 4 |
| Elongation at Break (Approx.) | – | 25-35% | 15-20% | 15-20% | 10-15% |
| Melting Point | – | 460° F | 480° F | 330° F | Chars @ 275° F |
| Abrasion Resistance | Most – 1 Least – 5 |
3 | 1 | 4 | 5 |
| Resistance to Rot | Most – 1 Least – 5 |
1 | 1 | 1 | 5 |
| Resistance to Acids | Most – 1 Least – 5 |
4 | 2 | 2 | 5 |
| Resistance to Alkalis | Most – 1 Least – 5 |
2 | 4 | 2 | 5 |
| Resistance to Oil | Most – 1 Least – 5 |
2 | 2 | 2 | 5 |
| Flexing Endurance | Most – 1 Least – 5 |
1 | 2 | 3 | 5 |
| Specific Gravity | – | 1.14 | 1.38 | 0.91 | 1.5 |
| Storage Requirements | – | Wet or Dry | Wet or Dry | Wet or Dry | Dry Only |
Breaking strength of natural fiber ropes up to 48 mm diameter as per IS standards (1084, 1321 and 1410) is as under.
| Diameter in mm | Breaking Strength in Kgf. | ||
|---|---|---|---|
| Manila Grade-I | Sisal and Manila Grade-II | Coir Grade-I | |
| 8 | 545 | 483 | 85 |
| 10 | 705 | 635 | 135 |
| 12 | 1065 | 955 | 195 |
| 14 | 1450 | 1285 | 270 |
| 16 | 2030 | 1805 | 350 |
| 18 | 2440 | 2135 | – |
| 20 | 3250 | 2845 | 545 |
| 22 | 3860 | 3405 | – |
| 24 | 4570 | 4065 | 790 |
| 28 | 6095 | 5325 | 1015 |
| 32 | 7875 | 6860 | 1320 |
| 36 | 9650 | 8635 | 1730 |
| 40 | 11940 | 10415 | 2135 |
| 48 | 16765 | 14735 | 3050 |
For more information on natural fiber ropes, please refer Indian Standards as under.
IS 1084: Manila Ropes – Specification. This standard prescribes the requirements of hawser-laid manila ropes of diameter 6 mm to 128 mm (A rope used in marine applications for towing and sometimes for mooring is called hawser).
IS 1321: Sisal Ropes – Specification.
IS 1410: Coir Ropes.
For ready reference technical specifications of 3 strand and 8 strand synthetic ropes made by Garware – Wall Ropes Limited, India are reproduced below.
Technical Specifications (3 Strand Ropes)
| Specifications | High Density Polyethylene Monofilament |
Polypropylene Parapro Monofilament | Polyamide (Nylon) Multifilament | Polypropylene Multifilament | |||||
|---|---|---|---|---|---|---|---|---|---|
| Circ. in Inches |
Dia (mm) |
Wt. /Coil of 220 mtr. in Kgs |
Breaking Strength Kgf |
Wt./Coil of 220 mtr. in Kgs |
Breaking Strength Kgf |
Wt./Coil of 220 mtr. in Kgs |
Breaking Strength Kgf |
Wt./Coil of 220 mtr. in Kgs |
Breaking Strength Kgf |
| 0.50 | 4 | 1.76 | 200 | 1.76 | 281 | 2.31 | 321 | 1.71 | 190 |
| 0.75 | 6 | 3.96 | 400 | 3.74 | 602 | 4.95 | 750 | 3.85 | 440 |
| 1.00 | 8 | 7.26 | 700 | 6.60 | 1061 | 8.80 | 1346 | 31.50 | 770 |
| 1.25 | 10 | 10.78 | 1091 | 9.90 | 1561 | 13.64 | 2081 | 10.00 | 1140 |
| 1.50 | 12 | 15.84 | 1540 | 14.30 | 2213 | 19.58 | 2999 | 15.20 | 1625 |
| 1.75 | 14 | 20.90 | 2091 | 19.80 | 3050 | 26.84 | 4100 | 21.00 | 2230 |
| 2.00 | 16 | 28.16 | 2805 | 25.30 | 3774 | 34.76 | 5304 | 26.80 | 2800 |
| 2.25 | 18 | 35.42 | 3468 | 32.56 | 4814 | 44.00 | 6701 | 34.10 | 3560 |
| 2.50 | 20 | 44.00 | 4274 | 39.60 | 5804 | 53.90 | 8303 | 42.00 | 4300 |
| 2.75 | 22 | 53.46 | 5080 | 48.40 | 6956 | 66.00 | 9996 | 51.00 | 5200 |
| 3.00 | 24 | 64.90 | 6100 | 57.20 | 8129 | 78.10 | 12036 | 60.00 | 6080 |
| 3.25 | 26 | 72.20 | 6936 | 67.10 | 9404 | 92.40 | 13974 | 70.00 | 7050 |
| 3.50 | 28 | 86.46 | 8211 | 78.10 | 10710 | 106.70 | 15810 | 82.00 | 8080 |
| 3.75 | 30 | 101.20 | 9486 | 89.10 | 12240 | 122.10 | 17748 | 94.00 | 9200 |
| 4.00 | 32 | 115.50 | 10710 | 101.20 | 13464 | 138.60 | 19992 | 106.00 | 10240 |
| 4.50 | 36 | 145.20 | 13464 | 128.70 | 16932 | 176.00 | 24888 | 135.00 | 12880 |
| 5.00 | 40 | 172.70 | 16320 | 158.40 | 20502 | 217.80 | 29988 | 166.00 | 15900 |
| 5.50 | 44 | 209.00 | 19635 | 193.60 | 24582 | 264.00 | 35802 | 212.00 | 19650 |
| 6.00 | 48 | 253.00 | 22848 | 228.80 | 28560 | 312.40 | 42024 | 240.00 | 21760 |
| 6.50 | 52 | 297.00 | 26418 | 264.40 | 33048 | 365.20 | 48858 | 281.00 | 25200 |
Technical Specifications (8 Strand Ropes)
| Specifications | Polypropylene Parapro/Monofilament | Polyamide Multifilament (Nylon) |
|||
|---|---|---|---|---|---|
| Circ. in Inches |
Dia (mm) |
Wt./Coil of 220 mtr in kgs |
Breaking Strength in Kgf |
Wt./Coil of 220 mtr in kgs |
Breaking Strength in Kgf |
| 3.0 | 24 | 57.20 | 8129 | 78.10 | 12036 |
| 3.5 | 28 | 78.10 | 10710 | 106.70 | 15810 |
| 4.0 | 32 | 101.20 | 13464 | 138.60 | 19992 |
| 4.5 | 36 | 128.70 | 16932 | 176.00 | 24888 |
| 5.0 | 40 | 158.40 | 20502 | 217.80 | 29988 |
| 5.5 | 44 | 193.60 | 24582 | 264.00 | 35802 |
| 6.0 | 48 | 228.80 | 28560 | 312.40 | 42024 |
| 6.5 | 52 | 268.40 | 33048 | 365.20 | 48858 |
| 7.0 | 56 | 312.40 | 37842 | 424.60 | 55998 |
| 7.5 | 60 | 358.60 | 43248 | 486.20 | 63852 |
| 8.0 | 64 | 407.00 | 48960 | 554.40 | 72012 |
| 9.0 | 72 | 514.80 | 61506 | 701.80 | 89964 |
| 10.0 | 80 | 638.00 | 75582 | 866.80 | 109956 |
| 11.0 | 88 | 772.20 | 90678 | 1049.40 | 130968 |
| 12.0 | 96 | 917.40 | 107100 | 1249.60 | 154020 |
| 13.0 | 104 | 1078.00 | 122400 | 1465.20 | 182070 |
| 14.0 | 112 | 1254.00 | 141780 | 1698.40 | 210120 |
| 15.0 | 120 | 1430.00 | 163200 | 1951.40 | 240108 |
For more information on synthetic ropes made by Garware-Wall Ropes Limited, please visit their web site – http://www.garwareropes.com
For more information on synthetic ropes, please refer following Indian Standards.
IS 4572: Polyamide multifilament ropes (Hawser-laid and plaited) – Specification. This standard specifies the requirements of 3-strand hawser-laid ropes and 8-strand plaited ropes made from continuous multifilament belonging to polyamide group.
IS 11066: Polypropylene ropes (3-strand hawser-laid and 8-strand-plaited) – Specification.
IS 5175: Polyester multifilament ropes -Specification (3-Strand Hawser laid and 8-Strand plaited)
Minimum Breaking Strength and Working Load Limit
The Minimum Breaking Strength (MBS) is the force that a given rope is required to meet or exceed in a laboratory test when it is new and unused.
Breaking Strength is the average force at which the product, in the condition it would leave the factory, has been found by representative testing to break, when a constantly increasing force is applied in direct line to the product at a uniform rate of speed on a standard pull-testing machine.
The Working Load (WL) is the weight or force applied to rope or cordage in a given application.
The Working Load Limit (WLL) is a guideline for the maximum allowable capacity of a rope product and should not be exceeded.
The Design Factor (DF) is the ratio between the MBS and WLL. This value is the margin of safety for an application.
In general, selection of a DF in the range between 5:1 and 12:1 is recommended.
Higher DF is selected for more severe application.
The term "Proof Test" designates a quality control test applied to the product for the sole purpose of detecting defects in material or manufacture. The Proof Test Load (usually twice the Work Load Limit) is the load which product withstood without deformation when new and under laboratory test conditions. For proof testing a constantly increasing force is applied in direct line to the product at a uniform rate of speed on a standard pull testing machine.
Use and Care of Ropes
Knots reduce the breaking strength of rope as much as 50%. Energy which is normally spread over the entire length of the rope directs itself to the knot. For this reason, splicing is preferred to knotting.
Sharp bends greatly reduce the strength of a rope. Use padding where possible.
Avoid all abrasive conditions. A rope will be severely damaged if subjected to rough surfaces.
Pulleys shall be free to rotate.
Rope will wear excessively when used with pulleys that are too small. Diameter of pulley groove shall be 1.2 times rope diameter. For nylon and polyester ropes, diameter of pulley shall be more than 8 times rope diameter.
If a rope is used over a round object having radius (known as bending radius r) less than 3.0 times rope diameter (d), reduce safe working load as under.
| Bending radius “r” | d | 1.5d | 2d | 2.5d |
|---|---|---|---|---|
| Reduction of safe working loads to | 60% | 70% | 77% | 82% |
Working Load Limit (WLL) is the maximum allowable capacity in vertical position. Give due consideration to the angle of spread while selecting rope / sling size.
Whenever a load is picked up, stopped, moved or swung, there is an increased force due to dynamic loading. In all such applications, stated working load limit (WLL) by manufacturer should be reduced by 1/3.
It may be noted that dynamic effects are greater on a low elongation rope, such as manila, than for a high elongation rope, such as nylon. It may be also noted that dynamic effects are more significant on short segments of rope as opposed to longer ones.
At higher temperatures, tensile strength reduces. At 100°C, it is lower by about 30% (or more).
Fiber ropes subjected to heavy loads for long periods of time can break well below catalog breaking strength. Natural fiber ropes such as Manila and Sisal have less ability to take sustained loads than synthetic fiber ropes such as nylon or polypropyle. Do not subject fiber rope to sustained loads for more than two days.
All ropes, synthetic or natural, should be kept away from rusting iron or steel. Rust can cause rapid loss of strength.
Insect ropes regularly. Avoid using rope that shows signs of aging and wear.
All rope should be stored in clean and dry place. They shall be kept away from extreme heat and out of direct sunlight. Some synthetic rope (particularly polypropylene, polyethylene, and aramid) may be severely weakened by prolonged exposure to ultraviolet (UV) rays.
