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Glenn Cockwell's Notes on Ropes

Working Loads 

Safe Work Loads of Fibre Ropes
3-Strand Ropes Safety factor = 5

(new rope)

Rope Diameter (cm/inches) Manila Nylon Poly-propylene Polyester Poly-ethylene
 

Kg.

Kg.

Kg.

Kg.

Kg.

0.64 (1/4")

54

136

113

136

114

0.79 (5/16")

90

227

182

227

159

0.95 (3/8")

122

317

227

318

227

1.27 (1/2")

239

567

377

545

363

1.59 (5/8")

400

908

590

863

477

1.91 (3/4")

490

1271

772

1090

681

2.22 (7/8")

699

1725

999

1544

953

2.54 (1")

817

2179

1317

1907

1135

 

Types of Fibre Ropes

Fibre ropes are made from either natural or synthetic fibres.

 

Pros

Cons

Natural Fibres
  • Resistant to heat
  • Do not burn fast
  • Hold simple knots
  • Susceptible to rot and mildew
  • Shrink and stiffen when wet
Manila  
  • Weakens when exposed to sunlight
Sisal
  • Sunlight resistant
  • Poor handling when wet
 

Pros

Cons

Synthetic Fibres
  • Stronger x3 than Natural fibres
  • Impervious to rot and mildew
  • Lighter
  • Do not stiffen when wet
  • Slippery when wet
Nylon
  • Strongest of all fibres
  • Highly elastic and will elongate 10% to 40%
  • High abrasion resistance
  • Lose 10% of their strength when wet
  • Very slippery when wet
  • Attacked by acids and paints
  • Dangerous when it snaps under load
  • Susceptible to heat and sunlight
Polypropylene
  • Light
  • Floats on water
  • Will not conduct electricity when dry
  • Weaker than polyester and nylon
  • Weakens progressively when temperatures rise (+65C)
  • Low melting point
Polyethylene
  • Resistant to acids and alkalis
  • Weakest of synthetic fibres
  • Softens with rising temperatures
Polyester
  • Lower stretch properties than nylon
  • No strength loss when wet
  • High resistance to sunlight and weather
  • Resistant to acids and alkali
  • Weaker than nylon under shock load

 

Safe use and storage

  • All ropes should be kept dry and away from chemicals
  • Never overload a rope
  • A frozen rope should be carefully allowed to thaw and dry before use
  • A rope should never be dragged over the ground or sharp objects
  • Avoid abrupt bends if possible as they weaken rope considerably. Pad all sharp corners
  • Synthetic ropes can be slippery when wet or new. Use additional care when handling or tying knots
  • Store ropes in a cool dry place with good ventilation. Hang loose coils over a peg
  • Dry and clean wet rope before storing. Allow them to dry naturally, as too much heat will make the fibres brittle.
  • Keep all ropes away from any source of heat.
  • Inspect ropes regularly for extreme wear and cuts
  • Untwist strands carefully and check for bright clean internal conditions
  • Pull out a couple of fibres from the end of a rope and try to break them. If they break easily then the rope should not be used when safety is required.

Knots, Bends, and Hitches

All knots bends and hitches reduce the strength of rope

Knots and bends by 50%

Hitches reduce by 25%

Splices by 20%

Monofilament ropes such as polyethylene and polypropylene require special knots to prevent slipping

Cutting Ropes:

Wrap tape around rope at the cutting point and then cut through the tape.

Information taken from a pamphlet issued by the Canada Safety Council and from information shipped with Lehigh rope.