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.
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.
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.
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 rope.
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.
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.
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!
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.
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.
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.
The HPS treatment reduces both stretch and creep of the line. The PU Coating in addition to protecting the braid from fraying makes it more compact and easier to splice. The ease with which UHMwPE splices is one of its greatest strengths. When you find a braid treated with PU Coating, the work is further simplified. The PU coating is particularly important where we leave the core uncovered. The treatment prevents it from snagging and fraying.
So when you go from a cruising rope to a racing one, the first change is the core. On a racing boat, with racing ropes, there are few applications where we find lines with polyester cores. As for the cover, we will now see how the reasoning is even more complex. If the superiority of the core in UHMwPE compared to PET does not raise doubts, for the cover we have to put together various considerations, from use to price.
Why add a cover to a racing line if the UHMwPE, be it Dyneema or another brand, is so performing? The melting point of UHMwPE is only 130 ° C, worse than polyester melting at 230°C. Furthermore, the PU Coating treatment makes the UHMwPE line very slippery. Perfect for sliding in a low-friction ring or thimble but absolutely not suitable for use in stoppers and winches.
If you’ve ever broken the cover of a rope with a Dyneema core, you’ll know what I’m talking about. The HMPE braid cannot be stopped either in a stopper or in a cam-cleat. And, if we used it uncovered on a winch it would have bad grip. That is, we would have to give a lot of turns on the drum for this to take hold. However, even if we managed to tighten it with the winch, we would not be able to block it in the self-tailer, effectively making the line unusable.
So why are there other coves besides the plain polyester ones? Although PET is respectable in its properties in the long run it tends to wear out at the working point of the stopper/cleats/clutches. For this reason we can protect the working point without upgrading the entire cover for its entire length. Those who are familiar with splicing and have good dexterity can apply a protective cover on the work points.
The important thing is to choose the right racing rope for the right application. And, if we are on a cruiser, we can rely on high quality lines in high tenacity pre-stretched polyester. However, with the improvement of technology even in the cruising sector, some upgrades cannot be ruled out. Fibre laminated sails have now become common even on boats that are not really pure racing ones. In this case we will probably have to change the related halyards as well. If we start to do some races, a better cover for genoa sheets and spinnaker / gennaker sheets is not to be excluded.
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