Choosing the right boat rope for the job depends on what you want it to do, says Rupert Holmes. Here's a quick guide to marine rope and its uses


At this time of year we often start to put into place plans for upgrading our boats for the new season. In many cases this will involve at least some work on replacing or improving running rigging, but it’s not always easy to identify the best type of boat rope for each function. Fortunately, in the case of marine rope the best kit for a specific task is rarely the most expensive.

Mooring lines, for example, benefit from being stretchy, as this reduces uncomfortable snatching in rough conditions. Nylon has plenty of stretch so is ideal for the purpose and is why it’s used for anchor rodes and as a snubber when anchoring with all chain.

Nylon has historically been one of the cheapest materials available for rope, arguably aside from polypropylene. The few boat owners who opt for polypropylene mooring warps invariably find its propensity to degrade quickly in ultra-violet light mean it’s more expensive in the long term. A faded and whiskery polypropylene rope has only a fraction of its original strength.

Of late nylon has become progressively more expensive, so dock lines are now more frequently made of polyester, often using a construction that enables the line to stretch. This is a fundamentally different approach to polyester rope intended for use as halyards and sheets, which are engineered to minimise stretch.

What’s the right diameter?

For sheets and halyards, it’s easy to assume that a chunky line made from a relatively inexpensive material is the perfect robust option for a cruising yacht. However, there are a number of problems with this approach and all too often I see people struggling to do what ought to be simple operations because of an inappropriate choice of rope.

Marlow’s Blue Ocean Dockline is a polyester product made from recycled plastic bottles. It has the same material properties as standard polyester rope. Photo: Marlow Ropes

Firstly, above 8mm diameter the thicker the line the more difficult it is to handle – there’s more bulk to coil, flake or stow. Increasing line size will also increase friction, which can be compounded by the  low-grade blocks and other deck fittings with which cruising yachts are often equipped.

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Oversized lines for anything other than mooring are therefore usually a route to an unbearable amount of friction. By contrast, reducing the size of lines tends to reduce friction. But won’t that make them weaker? Not necessarily – 8mm Dyneema is typically just as strong as 10mm double-braid polyester. In any case most lines fail through chafe and, of course, one that’s subject to less friction is less likely to chafe.

In addition, Dyneema has a slippery surface that’s intrinsically resistant to chafe. Granted the smaller Dyneema line will be more expensive than a double-braid polyester one a size larger, but possibly by as little as 25%, making gaining the advantages of Dyneema more affordable than it might appear at first.

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Is stretch really that much of a problem for cruising yachts? Yes – even if you don’t want to break any speed records it impacts the handling of a boat. In a gust you want the sails to be as flat as possible, but what happens when halyards stretch is that the sail shape becomes deeper. This produces even more power, so the boat heels more than necessary and starts to round up into the wind, making it difficult to steer.

When replacing lines it’s always worth taking a critical look at the associated hardware. If the mainsheet, for instance, has reached the end of its life, the blocks may not be far behind and if you are replacing a line with a higher tech option with less stretch the inevitable higher shock loads will often bring forward the point at which a worn-out fitting fails.

The cams of clutches wear over time, so may need attention even if they have held the old rope (with a rough cover) securely. Often the first time an owner realises the extent to which clutches are worn is when a shiny new rope slips. Fortunately, most manufacturers sell replacement cams, even for very old models, at a small fraction of the cost of a new clutch.

Extra jackets

If a line tends to slip even when the cams of the clutch have been replaced the best option is to splice an additional length of outer jacket around the line where it’s held in the clutch. This increases thickness locally, making it easy for the clutch to do its job. If the jacket is made of a material such as Technora it will also increase friction at the clutch, which again helps to prevent slip. 

Dyneema chafe jacket is extremely effective at preventing chafe at masthead sheaves. The primary mechanism for this is that the material is intrinsically slippery, but it also provides an additional physical barrier before any chafe reaches the structural core of the rope.

Don’t underestimate the effectiveness of this – I’ve seen halyards with Dyneema protection looking almost like new at the end of an Atlantic crossing. 

End for ending

It’s an easy maintenance task to forget, but end-for-ending can double the lifespan of a line. Simply mousing it out and reinstalling the other way round will give a fresh bit
of rope at all the chafe points, effectively doubling its service life. If you have to cut a splice off, a Selden halyard knot will suffice as an easy alternative to splicing an eye on old rope.

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