Racing ropes: making the right choice for each application

The world of ropes is much more full o variations than we might think. When we enter in the territory of racing ropes, things get even more complicated. The ropes for a sailboat seem at first glance all the same except for the colour. Nothing could be that far from reality. Some ropes have truly remarkable technical properties. Others are not quite as noble and we need to understand the differences.

Racing Ropes - Each cover designed for its use
Racing Ropes – Each cover designed for its use

Ropes, with some exceptions, are all made up of a core and a cover. The basic lines for cruising boats are often made with a polyester core and cover. Racing ropes mostly have a Dyneema ® or UHMwPE or HMPE core – which is to say the same thing. The cover, on the other hand, is usually a mix of two or more fibres where polyester is used to create the range of colours. The “noble” fibres used in racing lines usually have a limited range of colours.

Racing ropes: the world of noble fibres

Noble fibres distinguish themselves from common polyester for characteristics such as resistance, stretch and melting temperature. In fact, a polyester lines can be cut with a hot knife and finished with a lighter. For many of the high performance fibres this would not be possible. The melting point of Vectran is 350°C, that of Nomex® is 350°C – they are not even yet aramids. For aramids such as Technora®, Kevlar®, Twaron® we reach 500°C for Zylon® (PBO) at 650°C.

Racing ropes - The making of an anti-torsion cable
Racing ropes – The making of an anti-torsion cable

Among the high performance fibres everyone knows Dyneema®, this is just a registered trademark of the DSM company. Saying Dyneema is like saying Sellotape (a brand) instead of sticky tape. Dyneema is in fact composed of fibers of UHMwPE (ultra-high molecular weight polyethylene) or HMPE produced by Dupont. UHMwPE is 15 times stronger than steel and 40% stronger than many aramids of the same weight. This makes it an extraordinary fibre for making racing ropes.

HMPE also has extraordinary properties in terms of resistance to abrasion and chemicals. However, its melting point is just 150 ° C, even lower than polyester which melts at 260° C. For this reason, most racing lines have a Dyneema core (UHMwPE / HMPE) and a mixed fibres cover. This is to remedy the fact that in many applications, such as spinnaker sheets, a low melting point would be a problem.

Cruising ropes

For cruising ropes, the extraordinary holding properties and very low stretch of Dyneema are often useless. If, for example, we have Dacron sails, therefore able to stretch with every gust of wind, the HMPE rope becomes a bit wasted. On the other hand, when we have a sail that is also built with Aramids such as Carbon and Kevlar® fibres, we have no stretch. If we used a Polyester halyard for a noble fibres sail, it would be the halyard that “pumps” and stretches in a gust.

Cruising ropes
Cruising ropes

With a Dacron sail, on the other hand, the lengthening of the halyard and the sail are comparable, however they add up. In addition, both the Dacron of the sail and the Polyester of the rope stretch when left under tension. This lengthening over time is called creep, which differs from stretch, which is the instant elastic lengthening. So with polyester ropes and Dacron sails we have to be much more careful when we return to port not to leave everything in tension.

The typical example is that of the halyard of a furling jib. Many, once the sail is hoisted, tighten the halyard and do not touch it for the whole season. On many cruising boats the genoa halyard is not even led back to the coachroof winches. However, it would be good to remove the tension from the halyard when the boat is not in use, due to the creep the sail and rope will lengthen over time. Obviously this is nothing serious for the line, but the sail with a stretched leech will slowly lose its shape.

High tenacity polyester

Speaking of polyester, we cannot make a bundle of all fibres. In fact, even polyester can have very different properties depending on its quality. Polyester is part of that family of plastic materials made of polyethylene terephthalate. These include Sustadur Pet, Zellamid 1400, Arnite, Tecapet, Impet and Rynite, Ertalyte, Hostaphan, Polystar, Melinex and Mylar films, and the Dacron, Diolen, Tergal, Terital, Terylene and Trevira fibres.

Cruise ropes - HT Polyester on HT Polyester
Cruise ropes – HT Polyester on HT Polyester 

It is also indicated with the abbreviations PET, PETE, PETP or PET-P. The first polyethylene terephthalate fibre to be patented is Mylar, in 1943. PET plastic bottles are a 1973 patent. PET can therefore be transparent to make a film such as Mylar, or opaque to make a woven fibre to obtain Dacron. With reference to ropes we simply speak of PET but here too a world opens up.

The measurement of the density of the material expressed in grams per kilometre will inevitably indicate its final holding power. This density is measured in dTex, what we call “deniers” in other fields of yarn and fabrics. The greater the dTex grading of the single fibre, the greater the weight per meter and the breaking load of the finished rope. We therefore refer to high tenacity PET or HT (High Tenacity) for dTex values beyond a given threshold. So not all PET lines are the same and not all Dacron sails are the same!

Crusing lines cuts
Crusing lines cuts

Pre-stretched polyester

As long as we talk about polyester, we must be aware of the poor elongation properties of this fibre. At its breaking point, PET can reach a stretch equal to 12-15% of its length before tearing. Think, this is half the stretch of a Nylon fibre. Material that we find in our spinnakers and gennakers where the stretch actually absorbs and distributes the gusts. The actual stretch of the finished rope can be significantly reduced during the processing phase.

The elongation of the polyester over time is called creep and takes place by leaving a line under tension. However if we apply a programmed tension during the spinning of the fibre that we will use to weave the finished rope, it will have a reduced residual elastic stretch. This is why we speak not only of high tenacity PET but also of pre-stretched PET. Combining a high initial density that has also been pre-stretched we will obtain a PET rope with better properties.

Spools of cruising ropes
Spools of cruising ropes

However, neither stretch nor creep can be completely eliminated. But, it is important to understand that there are very low quality polyester lines even for a cruising boat. I realise that the price will not always help you make the choice. There are low quality products sold at the prices of completely different rope. Unfortunately, you will realise this at your expense as you find yourself having to continually which in a rope that continues to stretch and that will ruin quickly.

Evolution of cruising ropes towards racing ropes

Over time, therefore, the cruising ropes have changed a lot. Even among those in polyester, the stretch has been greatly reduced and the resistance has increased. However, to make step up in quality we are forced to change fibres. If, as far as the cover is concerned, it is rare to find anything other than PET, the core of the rope can vary in the cruising world too. If you think of a hoisted sail, on one side you have all the stretch of the sail.

Racing ropes - Monochrome polyester sock
Racing ropes – Monochrome polyester sock 

This is still made of polypropylene terephthalate (Dacron) even of the best quality, like the one produced by Bembridge. On the other hand, you have the halyard which, although pre-stretched and with high tenacity, will still have residual stretch. The sum of the two components certainly does not help the shape of the sail in a gust. As wind pressure temporarily increases, the simultaneous lengthening of the halyard and luff will carry the camber of the sail aft making it less efficient upwind.

Racing Ropes - Processing of a melange cover
Racing Ropes – Processing of a melange cover 

Dyneema was invented in 1963 but marketed by DSM starting in 1990. Another well-known brand that preceded Dyneema is Spectra. Many still today talk indifferently of Dyneema and Spectra, and to be honest they are both UHMwPE fibre ropes. However, even in the world of UHMwPE there are distinctions. In this case the unit of measurement is the atomic mass of the UHMwPE called Daltron. Many years ago also in the cruising world and especially in the racing ropes one saw the first ropes with a Spectra core.

Racing ropes: Dyneema and other UHMwPE fibres

Without going into too much technical detail, let’s say that Spectra is to Dyneema as a low quality Polyester is to a high tenacity one. Without speaking of atomic mass we can limit ourselves to making comparisons on the breaking loads between Spectra and Dyneema to see the superiority of the second. However, things get further complicated, even DSM that produces the Dyneema has introduced gradations. So you will hear about Dyneema SK75, SK78, SK99.

Racing Ropes - Processing of a protective cover
Racing Ropes – Processing of a protective cover 

Since this is a proprietary measure used by DSM, not referring to any unit of measurement in physics, unfortunately it helps us little in making comparisons. In other words, when we have a UHMwPE line of a brand other than Dyneema in our hands, how do we compare it to DSM’s Dyneema? For simplicity, it is best to compare the breaking loads of the braids with the same diameter. From this exercise it is clear that the Spectra does not reach the breaking load of an SK75 Dyneema braid. Other brands and products such as Southern Ropes’ Super-12® exceed the specifications of the SK75.

Therefore, when comparing the cores of two racing lines, if they are UHMwPE (also called HMPE), you will need to compare the braking loads. That is, just because a line says Dyneema instead of HMPE or UHMwPE doesn’t mean it’s better. Dyneema has simply become so well known that it replaces the name of the fibre that constitutes it. However, we have seen that those that have been sailing for long still speak of Spectra. In the end we all talk about UHMwPE or HMPE with better or worse properties.

Racing ropes: UHMwPE core treatments

The UHMwPE fibre can be treated before becoming a braid, a bit like PET which is pre-stretched. In the case of UHMwPE or HMPE there are two treatments that further improve its properties. The first is a hot pre-stretch process often referred to as HPS (Heat-Pre-Stretch). The second treatment is a protection with a polyurethane resin often indicated with PU Coating.