What are the qualities of different types of modern line and their uses?

17 October 2017

A novice sailor might be forgiven for thinking that ‘one rope is very much like another’ but, of course, this is very far from the truth.

With a wide variety of materials and types of construction now available to meet all needs (and budgets) it is worth giving some thought to what your boat needs before you go shopping for new line.

When buying line for use as running rigging such as sheets and halyards, you need to consider several factors, especially if you are racing. They are;

  • the propensity to stretch under load
  • the diameter required for the job
  • the durability of the line (i.e how the line stands up to UV light and chafing from clutches / winches, etc)
  • the weight of the line
  • other properties (such as bouyancy)

Lines used for anchoring and mooring should be strong enough for the vessel they are securing whilst at the same time being of the correct size to allow line handling and securing on the vessel’s cleats. Nylon and polyester lines are usually a good choice for dock lines because they stretch, making for a more comfortable time alongside.

Halyards and sheets (especially on a racing yacht) need to be strong and resistant to stretch. Specialist manmade fibres are now used regularly on racing boats. Minimal stretch, a high strength to weight ratio and ease of handling are all critical to your choice. Durability is also key to most decision making - unless you have very deep pockets.

Whereas a cruising yacht with dacron sails might happily use pre-stretched polyester effectively, a racing yacht with stiffer sails may benefit greatly from low stretch line made up of aramids such as Dyneema. The other benefit to using more exotic material is the reduction in size (and therefore weight) meaning that lighter halyards running up and down your mast’s length will be lighter and therefore substantially benefit your vessel’s stability performance.

Orange polypropylene line is regularly used for throwing line or Danbuoy. It’s major benefit being its light and floats (making a prop tangle more unlikely). Because it is light, most throwing lines have a weight attached to one end. 

It’s worth noting that if you upgrade your lines (especially your halyards) and reduce core size or cover material then you may need to make some changes to your clutches, blocks and self-tailers. There is no point reducing your halyard size to reduce stretch, only to find that they all now slip in your clutches or break deck fittings when loaded due to an increase in peak load due to the reduced stretch. 

As will all lines, knots and splices will further reduce its strength so make sure you allow for this when shopping for new lines. Check the data provided by the manufacturers.  

Most of us will be aware that 95% or so of a modern line’s strength comes from its core with the cover (usually a mix of materials) to provide a combination of ease of handling, heat protection, chafe protection and UV protection. An enthusiastic sheet trimmer on a larger racing yacht can easily melt a polyester cover on a winch drum in one overly enthusiastic ease whereas an aramid / polyester blend will better survive! 

It is possible to remove the cover from some lines to reduce weight without significantly reducing performance. However, this is at the detriment of easy line handling and a reduction in chafe and UV protection and is generally not to be recommended.

Finally, there is PBO. It stands for poly-phenylene benzobisoxazole compound rope and it is both very strong and extremely stretch-resistant. It can be used effectively as standing rigging, but it’s worth noting that whilst very strong for its weight, it is also liable to UV damage and chafe.

If you are unsure of what is best for your boat, check with a professional before buying.

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