Are you up to date with the changes in rope technology in recent years? Do you know which properties to select for the various different uses of rope on board? If not, you’re not alone – getting up to speed on the basics is not difficult.

Specifying sheets: how to choose the right rope

Sheets only experience full load when the boat is close hauled with the sails pinned in tight. As only a short length of the line is therefore under tension stretch is less of a problem than with halyards.

The four basic factors

Key properties defining a rope’s characteristics include its strength (breaking strain or safe working load) and elasticity – how much it will stretch for a given load. There are also two further important factors: resistance to degradation through exposure to sunlight. And for lines such as halyards that need to be held in a clutch, the ease with which the cam will grip the line.

Choose the right rope for stretch

For most purposes the aim is to minimise stretch for a given load, so that sail settings are maintained across a range of windspeeds. It’s worth noting that modern rope technology often means that a much thinner line can be used than a couple of decades ago. Compromises in the selection of rope tend to be driven by cost. Competitive racing yachts may spend significant amounts on rope and most cruisers have a more limited budget.

Mooring and anchoring, along with towing another vessel, are situations in which stretch is beneficial: it reduces uncomfortable snatching and the peak loads that are associated with this. Traditionally nylon has been used for these purposes, although it has increased in price. Further, polyester is now a more common choice for docklines: it is more pleasant to handle than old-fashioned three-strand nylon when it ages.

Choose the right rope for strength and budget

Halyard stretch: how to choose the right rope

Halyards are loaded for their entire length, so stretch can be a significant problem.

Mooring warps and anchor lines may be made of three strand or octoplait construction, which allow for more stretch. But most modern lines for running rigging are of a braided construction with a distinct core and outer cover. On a typical budget braid-on-braid polyester line aimed at cruising yachts the strength is shared fairly equally between the inner and outer components. However, core is responsible for the bulk of the strength of more high-tech ropes. The cover is more important in terms of providing abrasion resistance, protection from sunlight and improving handling and comfort.

Polyester is the most common single material used in modern ropes. But is only used on its own for applications where a little stretch isn’t seen as a problem. For this reason pre-stretched polyester is a popular choice for the mainsheet and genoa sheets of cruising yachts. These only carry their maximum loads over a relatively short section of the line, when the sail is sheeted in tight for sailing to windward.

Where budget is of paramount importance, polyester can also be used for halyards. However, given their long loaded length – around twice the height of the mast – there’s a lot more scope for stretch in a halyard than a sheet. A line that includes an aramid fibre, such as Dyneema or Technora will therefore make sense, particularly on a performance cruiser or a boat with low-stretch laminate sails.

Choosing advanced fibres

Aramids are strong, heat-resistant synthetic fibres. These have a minimal stretch that maintain a better sail shape as the rig loads up in a rising wind. In the past Kevlar and Vectran were also commonly used. But the latter suffers from poor resistance to ultra-violet light, while Kevlar has developed a reputation for failure without any visual warning as it ages. Kevlar cored lines are easy to identify, thanks to the material’s distinctive yellow colour. If your boat has any of these left they are liable to be nearing the end of their life and should be replaced. Even if there’s no outward evidence of chafe or other damage, these should be replaced.

The cover of a rope is often polyester, especially in cruising applications. However, this is frequently blended with aramids on high-specification racing yachts for heat protection. Cordura is used in covers on low-stretch halyards to provide a rougher surface that is easier for clutches to grip. By contrast, a Dyneema or Kevlar cover is very shiny and difficult to hold in a clutch. However, makes sense for sheets on a performance yacht as it makes it easy to unload them from a winch when tacking or gybing.

Matching the rope to the job

Many of the wide variety of very high performance ropes are intended for specific tasks on racing yachts. The owners of these racing yachts are happy to spend lots of money in exchange for a small performance benefit. That means there’s no guarantee that a more expensive rope will be the best for a specific task.

One problem is that, if you replace a line with one that has significantly less stretch, the peak loads experienced by the deck fittings and rig will be magnified. This can result in lines slipping in clutches or even hardware breakages.

Increasingly deck gear needs to be matched to the type of lines you’re using, This is the reason why before buying new running rigging it’s worth making sure everything else in the system is compatible with it. Clutch manufacturers, for instance, now frequently produce different jaws to match different rope materials. In many cases these can be retrofitted into existing units and can therefore be used to replace older worn jaws of the wrong profile.

It’s also important to know what the breaking strain figures relate to – unfortunately it isn’t consistent in the figures different rope manufacturers quote. Some specify the average breaking strain of an unspliced rope, while others provide a minimum figure for spliced lines. This minimum breaking strain is a lower number than the average breaking strain, and is reduced by a further 20 per cent in the quoted figures to account for the weakening effect of the splice.

Given the wide variety of rope types now available, if you have complex requirements riggers are often the only outlets that stock a full range. In any case they are in the best position to advise on matching lines with deck gear. However, good chandlers usually stock a reasonable selection of the most common lines used on cruising yachts and manufacturers are increasingly putting QR codes on their retail displays to enable customers to get more information about specific products.

Floating lines

These are generally made of polypropylene for use as rescue lines in man overboard situations. However, polypropylene is not idea for use in other marine applications – it has limited strength for a given diameter and tends to be rapidly degraded by ultra-violet light.

If you're considering improving your yacht's rigging, check out these practical articles: Choosing the right reefing system, How to tune the rig on your yacht and Understanding your rig: basic rig checks and common problems.

Written by: Rupert Holmes
Rupert Holmes has more than 70,000 miles of offshore cruising and racing experience, in waters ranging from the North Sea to the Southern Ocean and Cape Horn. He writes about all aspects of boat ownership and marine travel, including destinations, seamanship and maintenance, as well as undertaking regular new boat and gear tests. He currently sails around 5,000 miles per year and in the past couple of seasons has cruised from the UK to the Azores, as well as winning his class in the 2014 two-handed Round Britain and Ireland Race. He also owns two yachts, one based in the Mediterranean and the other in the UK.