special issue paper 1 design and performance of ropes for climbing

Design and performance of ropes forclimbing and sailingA J McLaren

Department of Mechanical Engineering, University of Strathclyde, 75 Montrose Street, Glasgow G1 1XJ, UK.

email: [email protected]

The manuscript was received on 16 September 2005 and was accepted after revision for publication on 10 March 2006.

DOI: 10.1243/14644207JMDA75

Abstract: Ropes are an important part of the equipment used by climbers, mountaineers, andsailors. On first inspection, most modern polymer ropes appear similar, and it might beassumed that their designs, construction, and properties are governed by the same require-ments. In reality, the properties required of climbing ropes are dominated by the requirementthat they effectively absorb and dissipate the energy of the falling climber, in a manner that itdoes not transmit more than a critical amount of force to his body. This requirement is metby the use of ropes with relatively low longitudinal stiffness. In contrast, most sailing ropesrequire high stiffness values to maximize their effectiveness and enable sailors to control sailsand equipment precisely. These conflicting requirements led to the use of different classes ofmaterials and different construction methods for the two sports. This paper reviews in detailthe use of ropes, the properties required, manufacturing techniques and materials utilized,and the effect of service conditions on the performance of ropes. A survey of research thathas been carried out in the field reveals what progress has been made in the development ofthese essential components and identifies where further work may yield benefits in the future.

Keywords: climbing, sailing, ropes, modelling, materials

1 ROPES FOR CLIMBING

1.1 Introduction

Climbing ropes are predominantly used for safetyand security. In particular, they must hold theweight of the climber in the event of a fall. The typeand magnitude of forces encountered depend chieflyon the type of climbing being undertaken. For con-venience, climbing activities may be split into threecategories: top roping, lead climbing, and abseiling.Detailed descriptions of climbing and abseiling tech-niques are available elsewhere [1, 2], but a briefdescription is given here to enable the reader toappreciate the context of the ropes’ use.

Top roping is the most common form of climbingcarried out at indoor climbing walls and is alsowidely practised on small crags or outcrops wherethe top of the route may be reached without climb-ing, perhaps by walking around the edge of thecrag. Figure 1 shows the typical arrangements fortop roping.

A fixed anchor point is set up at the top of the routeand the rope is looped through a karabiner attachedto this anchor. The two halves of the rope aredropped to the bottom of the climb to form asimple pulley system. The climber ties one end tohis harness while his partner, known as the belayer,secures the other end to his harness by the use of afriction device. This device allows the rope to betaken in or paid out under control, but can be quicklylocked to form a solid attachment to the rope. Theclimber ascends the route while the belayer takes inthe slack rope until the climber reaches the top. Atthis point, the climber may untie himself from therope and walk down to the bottom of the crag, ormay place his weight on the rope and be lowered tothe ground, under the control of the belayer, bymeans of the friction device. The latter practice isthe norm for indoor climbing walls.

Lead climbing is used in situations where the topof the route is inaccessible by any means otherthan climbing. Figure 2 shows the typical arrange-ments for lead climbing. This is typical of the

SPECIAL ISSUE PAPER 1

JMDA75 # IMechE 2006 Proc. IMechE Vol. 220 Part L: J. Materials: Design and Applications

climbing carried out on mountains or large crags. Inthis case, the lead climber ties one end of the rope tohis harness, while the belayer passes the ropethrough the friction device a few metres from thesame end. The lead climber begins to climb, towingthe rope behind him, and the belayer pays outslack at an appropriate rate. Periodically, the leaderwill stop and attach the rope to ‘running belays’.These are anchor points on the route, which mayconsist of pieces of equipment such as wedges or

camming devices that the lead climber carries withhim on the climb. These are placed temporarily incracks in the rock, and are designed to take theweight of the climber, should he fall. Alternatively,preplaced expansion ring bolts may be used. Ineither case, the rope is clipped to the anchor pointsby the use of a karabiner, which allows the rope tocontinue to run through the running belay as thelead climber continues the climb.

Once the leader has reached the top of the climb,or runs out of rope, he will stop climbing andattach himself securely to the rock. He then becomesthe belayer, while his partner climbs the route withthe security of a top rope. As he climbs, the partnerwill remove all the running belays as he passesthem, thus allowing their re-use at a later stage ofthe climb.

On mountains and large crags, where the route islonger than a typical 50 m rope, lead climbing iscarried out in a series of pitches. Once the secondclimber joins the leader at the belay, they organizetheir equipment and begin the process again. Inthis way, a large route or mountain may be brokeninto a series of short pitches, and the climbersprogress up the route as a self-contained unit.

Abseiling (also known as rappelling) is used todescend steep ground by sliding down the rope ina controlled manner. Climbers generally use thistechnique when descending or retreating frommountain routes. Friction devices, similar to thoseused for belaying, are utilized to control the rate ofdescent. Figure 3 shows the typical arrangementsfor abseiling. The usual technique is to double therope to allow its retrieval from beneath, once the

Fig. 1 Typical arrangement of ropes and anchor for

top roping, redrawn from Fyffe and Peter [2]

Fig. 2 Typical arrangement of ropes and anchors for

lead climbing; (a) the leader climbing, (b) the

partner following with the security of a top

rope, redrawn from Fyffe and Peter [2]

Fig. 3 Typical arrangement of ropes and anchor for

abseiling, redrawn from Fyffe and Peter [2]

2 A J McLaren

Proc. IMechE Vol. 220 Part L: J. Materials: Design and Applications JMDA75 # IMechE 2006

bottom of the abseil pitch is reached. On mountainroutes, this may involve the sacrifice of a piece ofequipment, which is left behind at the anchor point.

Modern mountaineering ropes are classified intofour classes, which are approved by the Union Inter-national des Associations d’Alpinisme (UIAA). Eachrope must be clearly marked with a standard labelindicating which class it belongs to.

Single ropes may be used on their own. They aredesigned for rock climbing on relatively straightpitches and routes that do not require abseil descent.These ropes are often 11 mm in diameter. Their useis common in indoor climbing centres, boltedsports routes, and relatively low crags.

Half ropes are used in pairs. The leader will clipone of the ropes into each running belay. This givesextra flexibility for belay placements. For instance,if climbing a broad crack with running belay place-ments on both sides, the leader will clip one ropeto runners on the left and the other to runners onthe right. In this way, each rope will run approxi-mately vertically, which will greatly reduce frictionaldrag. Half ropes have the additional advantage thatthey can be joined together for abseiling, thus dou-bling the distance that can be descended in onepitch. Half ropes are generally thinner than singleropes, typically 8 or 9 mm diameter.

Twin ropes are also used in pairs, with both ropesbeing clipped into each running belay. Their use isvery rare in the UK, but they are used in the Alps.Their diameter is generally similar to, or smallerthan half ropes, making them very lightweight.

The fourth category of ropes is the mountain walk-ing or tour rope. This is used to provide security onmountain walks, for glacier crossing, or ski mountai-neering. It is normally an 8 mm diameter dynamicrope, but is not suitable for rock climbing.

The properties that are required for climbingropes depend chiefly on their task of arresting thefall of a climber in a controlled manner. In toproping, the maximum fall that is possible is lessthan 1 m (provided the belayer is paying attention).However, depending on the vertical spacing ofavailable running belays, a leader may fall a muchgreater distance. Indeed, the fall distance will beapproximately twice the distance from the leaderto his last running belay anchor. In general, theavailability of anchor points, and/or the ability ofthe leader to hang on while placing them,decreases as the difficulty of the route increases.Indeed, falls of several metres are not uncommon.It is the function of the rope to absorb the energyof the falling climber, and bring him to rest, with-out transmitting large forces to his body throughhis harness. For this reason, relatively elasticropes, which stretch appreciably when loaded, aredesirable in climbing.

1.2 Fall forces

The design of a suitable rope for arresting the fall of alead climber requires an appreciation of the forcesthat are likely to be generated. Smith [3] reviewsand extends the analysis by Wexler [4] of the forcesgenerated in a lead climber’s fall. The geometry ofthis ideal fall is shown in Fig. 4. The maximumforce, Pmax (N) generated in the fall of a climber ofmass m, depends on the geometry of the fall andthe properties of the rope involved. This is given bythe following equation

Pmax ¼ mg 1þ

ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi1þ

2k

mg†H

L

s" #(1)

whereH (m) is twice the distance from the climber tothe running belay, L (m) the total length of rope used,g the acceleration due to gravity (9.81 m/s2), and k(N) the measure of the rope’s elasticity, defined by

P ¼ kx

L

h i(2)

where x (m) is the elastic extension of a rope of initiallength L (m) under an instantaneous load P (N).

It is clear that for a climber (and associated equip-ment) of a given mass, the maximum fall force maybe minimized by employing a rope with a low valueof k. This allows relatively large extensions, but gen-erates relatively small forces. An extreme example ofthis effect is the use of thick, highly extensible ropesfor bungee jumping.

The geometry of the fall may be characterized bythe ratio H/L. This is known as the ‘fall factor’, andis essentially a measure of the ratio of potentialenergy put into the rope by the falling mass to theamount of elastic material available to absorb thisenergy. Theoretically, values of fall factor arepossible between 0 and 2, with a fall factor of 2corresponding to a leader fall on steep ground withno running belays. (The leader will fall past the

Fig. 4 Geometry of the ideal leader fall, redrawn from

Smith [3]

Design and performance of ropes 3


belayer, the fall distance being twice the length of therope between them at the moment the fall begins.)

In practice, the geometry of leader falls is seldomthis simple. Climbing routes tend not to be straight,so the path of the rope becomes more convoluted,and where running belays are scarce, the rope maydeviate significantly from the ideal straight line.Pavier [5, 6] has developed theoretical models topredict the tension generated in ropes under a var-iety of fall geometries. His analysis takes into accountthe slip of the rope through the belay friction device,friction at running belays themselves, and avisco-elastic model for the rope.

1.3 Standards and testing

Experimentation has revealed that the generallyaccepted maximum load that the human body canwithstand without serious injury is 12 kN. Climbingropes must be designed such that this thresholdload is not exceeded, even in a relatively severe fall.The rope is of little use if it arrests the fall, but in sodoing transmits a fatal force to the climber. Theinternational standard test for climbing ropes isbased on a standard dynamic drop test [7] of rela-tively high fall factor.

The test uses amachine, known in the industry as a‘DODERO’, which performs the standardized droptest. This simulates a leader fall for a climber with afall factor of 1.78. This corresponds to a vertical falldistance of 5 m with a total rope length of 2.8 m.The rope passes through a standard ring that simu-lates a running belay, and it is generally the frictiongenerated between this point and the surface of therope that initiates the failure.

For a single rope, the maximum transmitted forcefor a mass of 80 kg is 12 kN. For double ropes andtwin ropes, a single strand is tested with a mass of55 kg and the maximum permitted load is 8 kN.Each rope must also withstand five consecutivestandard falls without failure. It is generally foundthat the rope stiffens after the first drop test, leadingto higher loads on subsequent drops.

In addition to the number of falls and maximumload criteria, ropes must conform to minimum stan-dards concerning knotability, extension under load,extension during standard falls, as well as sheathslippage, i.e. the amount of relative longitudinalmovement between the sheath and the inner core.A concise account of the standards is contained inthe short review by Bennett [8].

The implication of this test is that themost import-ant performance criterion for the rope is its energyabsorption characteristics. By nature, climbingropes will be designed to stretch significantly underload.

This has interesting consequences for the practiceof abseiling. The ideal rope for abseiling would berelatively inextensible. This is because significantoscillations tend to build up in the rope during des-cent. These are undesirable for two main reasons:the descending climber may be put off balance orbe disorientated if significant oscillation occurs; therope may be loaded over sharp edges and the oscil-lation can contribute to a sawing action which is det-rimental. For this reason, static ropes, with limitedextension, are used by people who participate inabseiling as an exercise in its own right, e.g. outdooractivity centres. However, since it is not practicalfor mountaineers to carry additional ropes for thissole purpose, they would normally abseil on theirdynamic climbing ropes.

1.4 Desired properties for rope

The desired properties for a dynamic climbing ropeare, therefore, as follows:

(a) high strength – ability to support static force andrepeated dynamic loading;

(b) known elastic properties that allow the rope tocontrol the force transmitted to the climber andequipment during a fall;

(c) lightweight;(d) durability – resistance to abrasion, ultraviolet

light, and repeated thermal cycling;(e) water resistance – stability of mechanical prop-

erties in the presence of water;(f) handling characteristics – feel, knotability, and

stiffness.

The first climbing ropes were made of naturalfibres such as hemp or manila. They evolved directlyfrom ropes used for general and marine applications,and were formed of twisted yarns. This type of con-struction is known as ‘hawser laid’ and generallyconsists of three parallel helical strands. The twistof the individual strands is in the opposite directionto the helix, and this twist locks and stabilizes thestructure. Figure 5 shows a hawser-laid hemp ropefrom the 1950s.

Although these ropes were adequate for simplesecurity and top roping, they were notoriously inef-fective at arresting leader falls. The old climbingadage, ‘the leader must not fall’, comes from anunderstanding of the likely consequences of aleader fall onto a natural fibre rope. The relativelyhigh stiffness of hemp and manila led to the gener-ation of large dynamic forces during falls. Smith [3]estimates that fall factors of 0.5 for hemp and 0.75for manila would be sufficient to cause failure.

The first advance towards modern ropes cameduring the Second World War, with the introduction

4 A J McLaren


of nylon fibres by DuPont. Initially, hawser-laidropes were constructed, substituting nylon fibresfor the natural products. The results were ropesthat could take a fall factor of approximately 1.0before breaking. These ropes, while superior tothose made from natural fibres, were notoriouslystiff if allowed to become wet. This made the tying(and untying) of knots difficult and greatly reducedtheir handling characteristics.

In 1951, the first ‘kernmantel’ ropes were producedby Edelrid. The structure of kernmantel ropes isshown in Fig. 6. The core (kern) consists of parallelbundles of twisted strands, each one of whichresembles a small hawser-laid rope. The individualstrands are often twisted in opposing directions(some clockwise and some counterclockwise). Thishelps to minimize excessive spinning or twist whileabseiling or lowering. The core is generally respon-sible for the mechanical properties of the rope withregard to tensile strength and dynamic behaviourand is covered with a braided sheath (mantel). Thepurpose of the sheath is to contain and protectthe core. However, the construction conditions ofthe sheath have significant effects on the propertiesof the rope, particularly its handling characteristics

and friction properties. Several authors havereviewed the factors influencing the construction ofmodern ropes and their effect on properties [9, 10].

1.5 Modelling of ropes

The literature on themodelling of textile ropes is lim-ited. Much of the research that has been carried outon rope structures is concerned with wire ropes,more commonly used in large engineering structuresand offshore applications. The standard text in thisarea is the book by Costello [11]. Several authorshave attempted to model textile fibre ropes. A goodreview of work in this area was recently publishedby Pan and Brookstein [12].

Manes [13] has applied wire rope modelling tech-niques to kernmantel climbing ropes, including pre-dictions of stress distributions during the DODEROdynamic fall test, where the rope is bent around abar of 10 mm radius. He also attempts to model thebehaviour over a 0.75 mm sharp edge, but his resultsare inconclusive. Contri and Secchi [14] haveattempted to model the cutting of a loaded rope bya sharp edge. Their approach considers the rope asa hierarchical structure of fibres/filaments, yarns/plies, strands, and overall rope, each component ofwhich may transfer load to its neighbours by friction.In this sense, their approach is similar to that ofLeech [15], who, with coworkers, has also publishedthe results of modelling work on the effects of cyclicloading on rope properties [16].

The mechanisms of rope failure have been studiedby Phoenix [17], who has analysed load transferbetween neighbouring strands in the rope. Failureof an individual strand leads to partial or total loadtransfer to adjacent strands by friction. The mechan-ical behaviour of rope structures is complex andhighly non-linear, which poses considerable pro-blems for modelling of failure mechanisms, particu-larly where contact forces, strain rate effects, andfrictional load transfer are concerned.

1.6 Environmental effects and service conditions

1.6.1 Rope age

Blackford [18] reviews several instances of rope fail-ure that have occurred since 1985. Her conclusionis that, with the exception of two incidents involvingchemical contamination (battery acid), the remain-der of rope failures are associated with cutting orabrasion over a sharp edge. An extensive review bySchubert [19] of rope failures among German andAustrian climbers since 1968 reveals the same pat-tern. Schubert tested a range of ropes of differentages (some as old as 30 years) using the DODEROstandard drop test. He reports that none of the

Fig. 5 Example of a hawser-laid hemp rope from the

1950s, after Schubert [19]

Fig. 6 Construction of kernmantel rope, after Pavier [6]



ropes tested failed after one test, and because realfalls are never likely to be as severe as the drop test,ropes are very unlikely to fail by breaking at a knot,running belay, or at a belay-friction device. Theonly likely instance where failure might be expectedis over a sharp edge [20].

Nevertheless, ropes may clearly be seen to deterio-rate with age. Schubert [21] uses the concept of‘metres climbed’ to characterize the age of a rope.He has studied the rate of loss of energy-absorptioncapacity with age (metres climbed). Some 50 percent of the energy absorption ability appears tobe lost in the first 2000–4000 m climbed, withreductions as large as 90 per cent after 20 000 m.He notes that the rate of ageing will depend on theseverity of use.

1.6.2 Water absorption

Polyamide materials are well known to absorb wateron contact. As all ropes (apart from those used atindoor walls) are likely to become wet through con-tact with rain, snow, or damp ground, it is necessaryto consider the effect of water absorption on theeffectiveness of the rope as a fall arrest system.

Cotugno et al. [22] reviewed the processes involvedin the absorption of water by polymeric yarns. Theplasticization effect of water causes reductions inelastic modulus and yield strength. This occurs bychanging the mechanisms of yield and deformation,as well as the cutting of polymer chains by hydroly-sis. The authors show that the equilibrium watercontent of a specific polymer is not sensitive totemperature, whereas the rate of absorption iscontrolled by diffusion, and is therefore stronglytemperature-dependent. Different polymers absorbwater to different extents. Polyamides tend to be‘hydrophilic’, i.e. the molecules possess specificsites that attract water molecules. The authorsreport research carried out by Mensitieri et al. [23]and Del Nobile et al. [24] comparing water absorp-tion in nylon-6 with a more hydrophobic ethylene–propylene copolymer. The nylon-6 absorbs tentimes as much water as the copolymer. This causeschanges in mechanical properties equivalent to areduction in the polymer’s glass transition tempera-ture. The degree to which water can affect mechan-ical properties depends on the exact nature of theinteraction between the polymer and the watermolecules. The authors report that the technique ofFourier Transform Infra Red (FTIR) spectroscopymay be utilized to identify these specific interactions[25]. Absorption of water, involving the establish-ment of strong hydrogen bonds between the watermolecules and the polymer, leads to high levels ofplasticization by the breaking of secondary bondsbetween adjacent polymer molecules. Polymer

systems that show weak interaction with watermolecules are plasticized relatively little by theaction of water.

Signoretti [26, 27] studied the effect of wetting ofropes on the results of DODERO drop testing. Hereports that the number of falls withstood is reducedto 30 per cent of the value for the original dry rope.This is true for both new and used ropes. He statesthat even brief immersion may have a seriouseffect, equivalent to a short rain shower. However,it should be noted that every rope in his studywithstood at least one standard fall, irrespective ofthe condition. This suggests that although waterabsorption has a significant effect, it does notrender the rope ineffective. He also tested ropestreated by the manufacturers with waterproofcoatings. He observes that these coatings stopwater sticking to the threads but do not stop waterabsorption in the molecules of the yarn. He statesthat the absorption of water has an equivalenteffect to an increase in temperature [28].

Signoretti also reports that the first fall on theDODERO for the wet ropes showed an increase inforce of 5–10 per cent. He proposes that this maybe due to increased friction between fibres inducedby wetting or possible swelling due to waterabsorption.

Recent work by Smith [29] has confirmed thatwater absorption has the most significant effect onstatic strength and stiffness. He also reports thatwater uptake appears to be more significant infresh water than in simulated sea water conditions.In both conditions, drying of the rope causes partialbut not complete recovery of the properties withrespect to those of the new rope. This is in agreementwith the findings of Signoretti.

1.6.3 UV light

Signoretti [30] has also examined the effect of UVexposure on the number of DODERO falls withstood.He exposed samples of rope to sunlight at mountainhuts in the Dolomites and tested both the staticstrength of filaments and the dynamic fall-holdingability. He reports a 35 per cent decrease in numberof falls after 3 months at the Kostner hut (2250 m),and 15 per cent reduction in number of falls afterexposure for the same time at the Carestiato hut(1834 m). He explains the difference with referenceto the intensity of sunlight at different altitudes.The decrease in dynamic performance of the ropesis greater than the difference in static strength ofthe filaments.

Photo-oxidation changes the chemical structureof the nylon molecules. This occurs by de-polymerization, leading to decreases in both energyabsorption and elasticity. The most common

6 A J McLaren


methods for reducing the rate of these processesinvolve the photo-chemical stabilization of thenylon, either by the inclusion of anti-oxidant pro-ducts or the incorporation of UV protection agents,similar to those used as filters in sunscreens.

UV light tends to have an effect on the appearanceof the rope. The fashion these days is for brightlycoloured and contrasting strands in the braidedsheath. Signoretti observes that decolourization ofthe sheath by UV exposure may be loosely correlatedwith loss of performance.

1.6.4 Freezing

Climbing during winter in the UK, and at all times inthe higher mountain ranges, exposes ropes to lowtemperatures, in all likelihood accompanied bycycles of wetting and drying. Odriozola [31, 32]observed a 30 per cent reduction in static resistancefor wetted and frozen ropes compared with the initialperformance of the dry rope. Signoretti [27] showsthat the number of falls withstood is reduced by50 per cent in the frozen condition. He reports thatthis is in agreement with the work carried out bythe Teufelberger company (Austria), reported bySchubert [33].

1.6.5 Heat glazing

McCartney et al. [34] have studied the effects ofheating due to rapid abseiling or sack hauling (onbig wall rotes, rucksacks are often hauled up behindthe climbers using pulley systems). These activitiescause localized damage to the sheath by frictionalmelting of a thin layer. Although the depth of meltingis generally small, it implies significant local temp-erature increases on the rope surface.

The authors report that the ultimate tensilestrength (UTS) of the core was not affected by externalglazing, but that the extensibility of the core strandsincreases by 40 per cent adjacent to the damagedside and by 20 per cent on the side opposite to theglazing damage. They propose that the temperaturehas locally been higher than the glass transition temp-erature, Tg, which alters themolecular arrangement inthe yarns, increasing amorphous proportion.

1.6.6 Particle entrainment

Pavier [35] observed a decrease in the number of fallssustained by ropes treated externally with grit par-ticles. Smith [29] studied the effect of sand absorp-tion on the static strength of ropes. Ropes wereconditioned by rubbing sand onto the surface ofthe sheath and tested in a tensile testing machine.He reports a 25 per cent decrease in static strengthwhen compared with the new rope. In addition, theobserved mechanism of failure was significantly

different from any other rope tested. The usualfailure mode involves catastrophic breakage of thewhole rope at the failure load, without prior warning.For the sand-treated samples, the sheath failed first,at relatively low loads, followed by progressive failureof the core at higher load values.

1.7 Summary

The property requirements for dynamic climbingropes are dominated by the need for effectiveenergy absorption in a leader fall. This demandsthat ropes not only be strong, but that they retainwell-controlled load elongation behaviour through-out their life. The materials and construction ofclimbing ropes have evolved from traditional naturalfibres, with a ‘hawser laid’ structure, to the modernkernmantel construction, consisting of paralleltwisted yarns surrounded by a braided sheath. Themajority of today’s climbing ropes are manufacturedfrom semi-crystalline nylon-6, the properties ofwhich are controlled by the relative fractions ofaxially aligned crystalline and amorphous phases.

Although environmental conditions and use doaffect the properties of ropes, notably by waterabsorption, UV light, freezing, heat glazing, and par-ticle entrainment, none of these factors is consideredto render ropes unsafe. The observation is that ropes,under all of these conditions, retain sufficientstrength and elasticity to sustain at least one stan-dard leader fall, and the conclusion is that moderndynamic ropes do not break in service. The exceptionto this pattern involves dynamic loading over sharpedges, which is said to have accounted for all buttwo of the reported rope failures in the past 35years, i.e. since the modern climbing rope wasdeveloped.

2 ROPES FOR SAILING

2.1 Introduction

Ropes are used to fulfil a variety of functions insailing boats. These may be broadly divided intotwo categories, namely, the standing and the runningrigging.

Standing rigging consists of structural componentsthat support the mast and spars, together withequipment such as guard rails, which are presentfor reasons of safety. By its very nature, standingrigging is semi-permanent and tends to be adjustedinfrequently, usually when setting up the mast atthe start of the day for dinghies or the start of theseason for yachts.

The running rigging is used to hoist and/or controlthe sails. Halyards are used to hoist the sails into



position; sheets are attached to the sails and areused primarily to control their angle to the boat’scentreline, and therefore the wind. The runningrigging will also generally include ropes that areused to control the position of moveable com-ponents of the boat, which are used for fine adjust-ment of the sails. The ropes in the running riggingwill generally pass through pulleys and blocks thatare used to control the line of action of the ropesand increase mechanical advantage. On yachts, thesheets and halyards are usually tensioned usinggeared capstan winches, which multiply the forcesexerted by the human body to the magnitudesrequired.

Standing rigging components are essentiallystructural. Traditionally, they were made of rope,but the most usual material in use today is twistedstainless steel wire rope. For high-performanceapplications, solid rod rigging, often made fromNitronic 50 (nitrogen alloyed stainless steel, aregistered trademark of Armco Inc.) is utilized. Thestrand moduli of a variety of standing riggingmaterials are shown in Fig. 7, replotted from thework of Gilliam [36]. Strand modulus is used inpreference to Young’s modulus; load extension datafrom an actual strand are used together with thenominal diameter of the strand to calculate theeffective modulus of the cable or rod.

The properties required of sailing ropes havemuchin common with those used for climbing. Theseinclude high strength, abrasion resistance, stabilityof properties in the presence of water, good handlingproperties, and low weight. However, in one import-ant respect, the property requirements are quitedifferent. Sailing ropes must have high levels ofstiffness. The requirement for energy absorptionin shock-loading conditions is removed. Indeed,the very elasticity which facilitates this ability inclimbing ropes would be a serious disadvantage forrunning or standing rigging components in a sailingcraft.

Elastic stretch in ropes used to control sails orother components would limit the precision withwhich adjustments could be made. For instance,the tension in a halyard has a fundamental effecton the three-dimensional shape of the sail and there-fore its aerodynamic behaviour. It is desirable to beable to make fine adjustments to halyard tensionwhile sailing because the sail-shape requirementsvary considerably with wind strength, point of sailing(the angle between the wind and the boat’s heading),wave conditions, and tactical considerations relatingto the position relative to competing boats.

Fine adjustment is facilitated by the use ofhalyards that possess high longitudinal stiffness.This is particularly important because halyardadjustments are usually made by the use of a winchin the boat’s cockpit. The total length of halyardbetween the head (top corner) of the sail and thewinch is approximately equal to the height of themast plus the distance from the mast to the cockpit.For a typical 10 m racing yacht, this distance mightbe �15 m. The full range of halyard tension is likelyto be accomplished by adjustments of 15 cm at thewinch, i.e. �1 per cent of the halyard length. Fineadjustment may require movements of ,1 cm,,0.07 per cent of the halyard length. Materials ofhigh stiffness are desirable because they allowropes of relatively small diameter to be used, whilestill supporting the considerable loads generated.Small diameter ropes not only save weight, import-ant in its own right for racing sailors, but alsoreduce the cross-section exposed to the wind. In ayacht that derives its entire driving force from theaerodynamics of the sails, any item aloft that doesnot contribute to this drive can only increase dragand/or healing force, with the associated reductionin efficiency.

While halyards are perhaps the most critical ropesfrom the point of view of fine adjustment, the samerequirements certainly apply to most other com-ponents of the running rigging. Sheets that controlsails may be highly loaded, particularly when sailingupwind, when the sails are pulled tightest. Wincheson racing yachts are characterized by their powerratio which is defined as the ratio of sheet loadproduced, divided by the force applied to thehandle. For a typical 10 m racing yacht, wincheswith a power factor of �40 might be expected.Therefore, a relatively light crew member, say 80 kgin weight, exerting one quarter of their body weightas a force on the winch handle, might be expectedto generate a sheet load of 8 kN. It is interesting tonote that this is equal to the maximum loadpermitted for half ropes and twin ropes in thedynamic drop test for climbing ropes. In reality,loads far in excess of this value might be expectedin sailing ropes.

Fig. 7 Elastic properties of various candidatematerials

for standing rigging, re-plotted from Gilliam [36]

8 A J McLaren


2.2 Materials and construction

An excellent review of ropes for sailing has recentlybeen published by Pawson [37]. He reviews thehistory of rope materials from the early naturalfibres such as hemp, manila, and sisal, through thediscovery of nylon in the 1930s and the later develop-ment of polyethylene (PE), polyester (PES), andpolypropylene (PP). Of the man-made fibres, nylonis not particularly suitable due to its high stretch(the very property that makes it ideal for climbingropes). The high degree of stretch makes it unsuita-ble for halyards and sheets, for the reasons alreadyexplained. In addition, should a loaded nylon ropebreak, it tends to whiplash severely. However,nylon is often used for mooring ropes where a certaindegree of elasticity is an advantage, as in the dampingof snatch loading.

The majority of sailors use PES ropes for runningrigging. The ropes are heat treated and prestretchedin the manufacturing process to give high longitudi-nal stiffness. The construction generally consists of a‘braid on braid’ structure; formed from braiding aneight- or sixteen-strand hollow plait over a core ofanother hollow braid. These ropes give excellentfriction and handling properties, in addition togood stiffness.

PP is cheaper than PES, but its wear and UV resist-ance properties are inferior. It has relatively low den-sity, which makes it float, which can be an advantagefor some applications, e.g. floating heaving line forman overboard situations.

2.3 Exotic materials

At the high-performance end of the sport, e.g. theAmerica’s Cup, considerable development has beencarried out into the use of exotic specialist materialsto reduce weight and increase performance. The firstexample in use was the aramid fibre known as Kevlar(a registered trademark of E.I. DuPont de Nemours).Alternative trade names include Twaron (a regis-tered trademark of Teijin Twaron USA, Inc.) andTechnora (a registered trademark of Teijin Co.,Ltd). It shows very low stretch, is very strong, andlightweight. However, its properties in bending aresomewhat poorer, particularly over pulleys andsheaves, and this has led to the development ofblocks with larger sheaves to alleviate this problem.All these fibres must be protected from UV degra-dation and chafe, and for this reason, the core ofthe rope is constructed from the specialist fibre,whereas the braided sheath is usually made fromPES.

Another fibre, now in relatively common use, ishigh-modulus polyethylene (HMPE) sold under thetrade names Spectra (a registered trademark of

Allied Signal/Honeywell) and Dyneema (a registeredtrademark of DSM Corp). This light, strong fibre hasalso found uses in climbing. It is used to make tapeslings and static cord for use in running belays. Thedynamic properties of the rope absorb the energyof the fall, but the protective gear placed in therock is designed as a lightweight, strong, stiff butflexible structure. Here, the weight savings that arepossible for a climber carrying a large assortmentof protection equipment have led to the adoptionof exotic materials.

Most recently, the liquid crystal polyester (LCP),sold as Vectran (a registered trademark of HoechstCelanese Corp), and p-phenylene-2,6-benzobisoxa-zole (PBO), sold as Zylon (a registered trademark ofthe Toyobo corp), have been used by America’sCup teams, and are starting to make their way intothe regular racing market.

None of these most recently developed fibres ischeap, but as with many sports, competitors willreadily spend money on materials and equipmentthat give a perceived advantage, however small thismay be in reality. Certainly, there would seem to bemore scope for the use of novel and exotic materialsfor sailing ropes than for climbing. The cost of ropesand cordage as a fraction of a racing boat’s budget isrelatively small, whereas for the average climber,their rope or ropes constitute a major fraction ofthe total cost of the equipment they own.

2.4 Knots and splices

Both sailors and climbers need to make loops in theend of their ropes for various purposes. Climbers tra-ditionally tied the rope round their waist with a bow-line knot, but since the development of good-qualitysit harnesses, the usual method is to tie the end of therope to the harness by use of a double figure-of-eightknot. The current advice on the use of knots byclimbers in contained in the BMC’s excellenttechnical booklet [38].

Sailors also traditionally use knots to make loopsin the end of a rope. In particular, the bowline isgenerally used to attach the sheets to the clew(bottom, rear corner) of a headsail. This knot iseasy to tie and can be untied quickly once unloaded.This is better than a permanent attachment becauseany rope tangles can be quickly sorted out by unty-ing the knots if necessary. Sheets also tend to bestored below deck when not in use, so need to beattached to the sail on each occasion that the boatis raced.

Recent work [39] utilized static tensile testing tomeasure the strength of a variety of knots and splicesused to make loops in the end of PES sailing ropes.Four knots were evaluated bowline: double bowline,perfection loop, and double figure-of-eight. All knots



broke at between 55 and 84 per cent of the ropestrength, with the double figure-of-eight beingsignificantly stronger than the others. This result islikely to be reassuring to climbers who use thisknot for tying into their harness, but for sailors, theknot’s extra strength is outweighed because it isrelatively difficult to untie once it has been loaded.The authors also examined the strength of splicesused to make loops in hawser-laid as well as braid-on-braid ropes. Compared with knots, splicesprovide a significantly stronger loop. However, theycan only be used where the loop is required to besemi-permanent.

Other workers [40, 41] have addressed the subjectof splices and end terminations for both steeland polymer fibre ropes. The non-linear nature ofthese materials and the complexity of their struc-tural interactions make modelling in this fieldchallenging.

3 FUTURE DEVELOPMENTS

Pawson [37] gives an insight into future develop-ments in sailing ropes in his review. Current ropes,which have cores made from the exotic materialsdescribed in section 2.3, are generally protected byuse of a PES (or occasionally PP) cover. The strengthand extension properties of the rope are governedby the core material, so traditional braid-on-braidsplices are inappropriate for these constructions.Manufactures have designed new splicing tech-niques in order to make core-to-core splices. Thepractice of stripping off the cover and using thecore alone is commonplace, particularly for ropesthat form standing rigging components such as back-stays or spinnaker pole bridles. The tails of sheetsand halyards cannot be used without the coverbecause this makes for difficult handling usingwinches and jammers. The solution is the produc-tion of tapered sheets and halyards, stripped at theworking end but covered at the tail.

Future developments are likely to involve theinclusion of exotic materials in the structure of thecover itself. Pawson [37] mentions several examples,mostly from developments for America’s Cup teams:covers have been used that contain prestretchedDyneema, over cores of Vectran, Dyneema, or PBO.Covers containing PBO have also been developedto give greater wear resistance. Despite the fact thatthese ropes are very expensive, their use actuallysaved money because the standard PES coveredropes needed to be replaced after each race. Therelatively poor UV resistance of PBO is not seen asa problem because the ropes need to be replacedfor reasons of wear after two race series, longbefore the effects of UV become apparent.

Other manufactures have developed coverscontaining Nomex (a registered trademark of E.I.DuPont de Nemours) or Aramid fibres. These helpprevent melting due to frictional heating on winchdrums when sheets are being eased. These ropesmay lead to scoring of carbon fibre winch drums,so rope and winch manufactures are workingtogether to solve these problems.

It remains to be seen to what extent these develop-ments from the extreme top end of the sport willpropagate down to club and regatta sailors. However,it is interesting to note that parallel developmentshave occurred in the materials and constructionmethods used in sail making. It is common to seethe same club and regatta sailors using laminatesails, reinforced with such exotic materials asKevlar, carbon fibre, and Vectran. This may indicatethat more exotic, high-performance ropes will startto be used by sailors outside the elite group.

In contrast, the average climber is unlikely to bewilling to pay a high premium for a small increasein performance. The general conclusion from thestudy of climbing accident statistics is that ropes donot break, other than when loaded over an edge.Reasonable weight savings have been achieved bythe use of smaller diameter ropes, particularlyamong sports climbers. However, larger weightsavings are possible by enhanced design of runningbelay equipment, and this has seen considerabledevelopment in recent years. Improved rope coat-ings may increase UV resistance and reduce waterabsorption, which will be of benefit to mountaineers.

4 CONCLUSIONS

The apparently similar ropes used by sailors andclimbers are, in fact, very different. The majordesign constraint for climbing ropes is the require-ment to absorb and dissipate the energy of leaderfalls, without transmitting large forces to the climber.This requires a rope of moderate to low longitudinalstiffness, but high strength. This is achieved by theuse of polyamide nylon-6, formed into a kernmantelstructure of parallel twisted yarns surrounded by abraided protective sheath.

Environmental damage due to ageing, waterabsorption, UV light degradation, freezing, heatglazing, and particle entrainment has a significanteffect on the properties of the rope and decreasesthe ability to withstand standard drop tests. How-ever, none of these treatments reduces the propertiesof the rope to levels that would cause failure in use.The most significant threat to safety is the cuttingof a rope that is loaded over a sharp edge.

The relationship between structure and propertiesis complex, and although the problem of describing

10 A J McLaren


it has responded to various modelling techniques,there is still scope for further work in this area.

Sailing ropes, especially for boats involved in racing,require a different portfolio of properties. In particular,high longitudinal stiffness to weight ratios are domi-nant constraints. Precise control of sails and otherequipment by rope actuators leads to the need forlow-stretch materials. Traditional natural fibres havebeen replaced by man-made polymers, notably PES,formed into ropes with a braid-on-braid structure.

In high-performance applications, more exotic corematerials, usually covered with a braided PES sheath,are used. These materials give enhanced stiffness toweight ratios, but incur a considerable monetarycost. Although their use was initially confined to thetop echelons of competition, they are becomingmore widespread at all levels of the sport.

Loops may be formed at the end of ropes by bothknots and splices. Spliced loops are significantlystronger than knots, but their use is restricted tothe manufacture of semi-permanent loops.

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APPENDIX

Notation

g acceleration due to gravity (m/s2)H twice the vertical distance between the

climber and the last running belay (m)k rope elasticity (N)L total length of rope used (m)m total mass of lead climber and equipment

carried (kg)P instantaneous load transferred to the

rope (N)Pmax maximum load transferred to the

rope (N)Tg glass transition temperature (8C)x instantaneous elastic extension of the

rope (m)

12 A J McLaren


special issue paper 1 design and performance of ropes for climbing

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