Ropes

FIBRE ROPES

Natural fibre ropes manila, hemp and sisalMan made fibre ropesNylon the strongest of the man made fibres, it gas high energy absorption and the ability to endure heavy repeat loading. When in water it sinksPolyester has a good abrasion resistance and a lower extension than most synthetic ropes. It has equal strength when wet or dry. It sinks in waterPolypropylene the most common type of mooring rope due to its ability to float. It is of equal strength wet or dry. Advantages and disadvantage of fibre ropesAdvantageDo not meltGives audible warning if breaking point is approachingDo not recoil as much as synthetic when brokenNot susceptible to moderate heat and sunlight damageCan be surged and rendered on drum endsCan be opened up for internal inspection without damaging the ropeEasily spliced

Advantages and disadvantage of fibre ropesDisadvantagesSusceptible to rot and mildewNot as strong as synthetic ropes as the same sizeHas small stretching abilityNot easy to handle.Has a tendency to swell and stiffen with age and damp which makes large mooring ropes difficult to work withIf wet can freeze in very cold conditions.

Care and handling of fibre ropesAll synthetic fibre ropes have varying qualities of resistance to chemicals, acids, alkalis , etc, they should be stowed in well ventilated dry compartments away from such material.Do not stow on deck, even for short voyagesKeep mooring ropes covered as exposure to strong sunlight is detrimental to ropes.Stow on gratings.Do not stow near heat e.g. engine roomInspect regularly internal and external for wear and tear.Eye splices should have not less than 4 tucks Avoid over loading the ropes around sharp anglesWash rope with fresh water if being splashed by corrosivesCare and handling of fibre ropesKeep wires and other ropes in different leadsSections of ropes which are prone to abrasion should be protected by leather sheathsSynthetic ropes have low melting points, therefore do not surge or render on drum ends. Do not use more than 3 turnsAlways stopper with the same kind of rope.No audible sound before a synthetic rope parts.Breaking strengthManila = 2D2/300Poly propylene = 3D2/300Terylene = 4D2/300Nylon = 5D2/300

WIRE ROPESModern wire rope was invented by the German mining engineer Wilhelm Albert in the years between 1831 and 1834 for use in mining in the Harz Mountains and was quickly accepted because it proved superior to ropes made of hemp or to metal chains, such as had been used before.Wilhelm Albert's first ropes consisted of wires twisted about a hemp rope core, six such strands then being twisted around another hemp rope core in alternating directions for extra stability. Earlier forms of wire rope had been made by covering a bundle of wires with hemp.

Manufacturing a wire rope is similar to making one from natural fibres. The individual wires are first twisted into a strand, then six or so such strands again twisted around a core. This core may consist of steel, but also of natural fibres such as sisal, manila, henequen, jute, or hemp. This is used to cushion off stress forces when bending the rope.This flexibility is particularly vital in ropes used in machinery such as cranes or elevators as well as ropes used in transportation modes such as cable cars, cable railways, funiculars and aerial lifts. It is not quite so essential in suspension bridges and similar uses.Wire rope is often sold with vinyl and nylon coatings. This increases weather resistance and overall durability, however it can lead to weak joints if the coating is not removed correctly underneath joints and connections.

Safe working load- is the stress that a component of a lifting apparatus can safely bear in normal useBreaking stress or strength is the stress at which a component will fractureFactor of safety is a factor used to divide the breaking stress to obtain the safe working load. It is usually 4 to 8. for wire rope it is 5 and fibre rope is 6

BREAKING STRENGTH6 strand, 12 wires per strand 15d2/5006 strand, 24 wires per strand 20d2/5006 strand, 37 wires per strand 21d2/500

SWL must be clearly marked on every component of the lifting gear

Ordinary lay The lay of wires in each strand is in the opposite direction to the lay of the strands that form the wire. Lang's lay The lay of wires in each strand is in the same direction as the lay of the strands that form the wire. Alternate lay The lay of wires in the strands alternate around the rope between being in the opposite and same direction to the lay of the strands that form the wire rope. RIGHT HAND LANG LAY

LEFT HAND ORDINARY LAY

6x19 FC RH OL FSWR

6 Number of strands that make up the rope 19 Number of wires that make up each strand FC Fibre core RH Right hand lay OL Ordinary lay FSWR Flexible steel wire rope

Distortion of the rope by kinking, crushing, crippling, etc, is likely to reduce the strength of the rope by 30%.At sub zero temp the steel wires will brittle and the rope may part with out warning. Further the flexibility is reduced. How ever the wire will regain its normal characteristics.Wire rope is declared unfit in length of eight diameters the total number of visible broken wires exceeds 10% of the number of wires in the ropeE.g. consider wire rope with a diameter of 24 mm. suppose it is a six stranded rope with 24 wires in a strand . The total number of wires is thus 144. hence if any length of roughly 19cm the total number of visible broken wires exceeds 14, then the wire is condemned unfit.The wire is also declared unfit for use if corrosion, wear, etc is considered excessive by the person inspecting.