Chain or Rope: A Weight, Stretch, and Strength Accounting for Raising Water and Loads

Steel chain is often chosen for raising water because it tolerates abrasion, sunlight, and neglect better than rope, while rope is chosen because it is light and easy to handle. This paper compares three systems in a nominal breaking-strength class around 30 kN — a 10 mm steel chain with a stated breaking strength of 32.0 kN and a mass of 2.20 kg/m, a 20 mm manila rope at 28.0 kN and 0.310 kg/m, and a 14 mm polyester rope at 32.0 kN and 0.120 kg/m — carrying a payload of 11.0 kg made of 10 litres of water and a 1.0 kg bucket, from depths of 5 m, 10 m, 20 m, 30 m, and 50 m. Chain weighs 18.33 times as much per metre as the polyester rope and 7.1 times as much as the manila rope. At a depth of 5 m the chain alone already weighs 11.0 kg, exactly the payload, and the total suspended mass is 22.0 kg; at 50 m the chain system totals 121.0 kg against 26.5 kg for manila and 17.0 kg for polyester, and the energy required for the lift is 32373.0 J for chain against 9196.9 J for manila and 6867.0 J for polyester. Against a stated comfortable hand-lifting limit of 20.0 kg total suspended mass, chain crosses the limit at a depth of only 4.09 m, manila at 29.03 m, and polyester at 75.0 m. Chain's compensating virtue is low stretch: at working load it elongates by 0.8%, giving 0.4 m at 50 m, against 6.0% and 3.0 m for manila and 4.0% and 2.0 m for polyester. The decision rule that follows assigns chain to shallow, abrasive, or mechanically wound duties, polyester rope to hand lifting from all but the shallowest wells, and manila to intermediate depths where its handling and cost are valued and its stretch and decay are accepted.