Rope Measurement Information

Rope Diameter

Rope is manufactured on complex spinning and weaving machinery.

The amount of yarn per metre is accurately calculated and strictly controlled to produce a finished rope with the correct interacting tension (or lay) at a nominal diameter, normally in 2mm increments in even numbers e.g. 8mm, 10mm, 12mm
1mm increments are also available in some ropes e.g. 7mm, 9mm

Importantly, the final break load of the rope for any given diameter is dependent on the quantity/weight of yarn per metre in the designated construction.

Rope manufacturers publish minimum (or average) break loads for their ropes and therefore all rope production is designed to achieve this rather than concentrating solely on the finished diameter.

New ropes are generally 'fatter' than their given diameter.

When your new rope arrives, it will be 'relaxed' and may look a little 'fat'

Attempting to measure the diameter - by eye, with a tape measure or even callipers - before it has stretched out to a working diameter isn't likely to produce an accurate result.

The true diameter will be more apparent if you hold the rope firmly with one hand, take a firm grip with the other hand and run the rope through your grip without releasing the pressure - a leather glove will protect your hand if required.

Once you have used (and stretched) your new rope, it will become thinner (and longer) and should measure more closely to the nominal diameter.

N.B. Most of the feedback we receive on rope diameter is that the rope is too fat.
The most common causes for this are:

  1. customers erring on the up side when ordering
  2. measurement before use
  3. relaxation of the rope construction

Of course, there is the possibility that we may have sent you the wrong rope, but it is extremely rare.

Marine Rope Manufacturing Machine

Rope Length

Rope manufacturers wind rope onto reels under tension to produce a very neat finish.

When the rope is pulled off the reel and left in a heap on the floor (or in a parcel) it will 'relax' i.e. get fatter and shorter.

The stretchier the rope, the more it will 'relax'

Jimmy Green Marine allow for this when measuring your order by adding an appropriate percentage according to the elasticity of the rope i.e. the stretchier it is, the more we add on to compensate.

We also strive to ensure that all spliced/finished lengths are accurate for e.g. short strops and generous for e.g. halyards or sheets.

Even clearance ends that have been accurately measured with the appropriate extra percentage allocation may arrive in a further relaxed state.

If you feel the need to check the length of your rope, please make off one end and pull the rope taut while running the rope through your hand (a leather gardening glove is a good protective layer) to offset the 'relaxation' and establish the true length.

Laying it loosely on the floor to measure a few metres, turning it on the floor and laying it down again repeatedly is likely to lead you to the disappointing conclusion that it is short.

Of course, there is the possibility that we may have measured the rope incorrectly by mistake, but it is extremely rare.

If you have any issues with your rope purchase, please email or ring 01297 20744 and speak to one of our Rigging Sales Team for futher advice or information.

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