Pre-stretched Polyester Ropes
!!Pre-stretched polyester ropes.
(Based on a thread on Change-Ringers, May 2005, summarising contributions from John Harrison, Matthew Higby and Philip Pratt).
Pre-stretched polyester is similar to 'Terylene' which is a commercial brand-name. It is a good material for the top end of bell ropes because:
- it does not shrink in damp weather
- it does not go stiff in damp weather
- it is not springy when new
- it lasts almost indefinitely
Two manufacturers supply products which have been used in towers, Marlow and English Braids. The Marlow rope has orange and black tracers in the rope, while the one from English Braids has blue. Marlow rope has been found to be less springy and is preferred by most users.
!Marlow Rope Specifications
Users of Marlow rope have suffered some confusion as the specification has changed at times. A military specification rope, with far less stretch, has similar colour markings to the sailing grade. The sailing grade rope in 10mm diameter is suitable for short ropes (up to about 8m), but displays more spring on long draughts. Upgrading to 12mm diameter is recommended in this case.
The part number is important, because the MOD/navy spec rope has a different part starting with AE not AC. The AC type is the sailing rope, whereas the AE is the MOD spec version. To obtain a copy of the technical specification of this rope you will need to contact the MOD, because Marlow are not allowed to release any details of this rope without consent of the MOD, if at all. The technical specification for the AC sailing type of rope is available from Marlow in the form of a PDF file.
According to to the technical branch of Marlow Ropes there is no theoretical difference between the two types in terms of their stretch characteristics. The identifiable difference between the ropes is a slight change in colour of the red/orange fleck. AC has a burnt red fleck, and AE has a distinct orange. The AE type of rope is produced to what they call 'British Standard' and is overspec'd in its load characteristics (and is a little larger in diameter), to guarantee that the rope will be consistent from reel to reel, and will not break below a certain load. The heat treatment process is also probably a lot more consistent and thorough; the details of this are apparently contained within the MOD technical specification sheet, which they are not able to release.
The 10mm AC type of rope has a breaking load of over 2300kg (it could singly carry the dead weight of up to a 46cwt bell) which, in terms of its use in bell ringing, is not remotely approached.
Since ringing never reaches more than 5\% of the break load of the rope, and there may still be stretch (typically 1\% extension which makes a huge difference) we should look at increasing the spec of the rope to either 12 or 14mm diameter so we never get above say 2 or 3 \% of its total break load and thus 0.5\% or less stretch.
Pre-stretched polyester rope can be short-spliced by hand and can also be machine spliced. Theoretically (because of the differing coefficients of friction) it should not be long-spliced with natural fibre rope, but there are several reports of this being achieved successfully in practice.
David Beacham writes: I have had no trouble at all with joining polyester to flax with a conventional long splice, which you need to do if some part of the rope passes over an intermediate pulley. (If you use a short splice in this situation, you will feel the "bump" as the splice runs over the pulley.)
Mark Davies writes: I agree with David, I've long-spliced flax to poly without problems, and the splices have lasted many years. When tucking the ends in, you can't "comb out" polyester so well as natural yarn, since the fibres don't come loose. However, you should still use the comb, and tuck in as usual as best you can. If you like, you can trim half the ends of each poly strand in order to get a neater result. On NO ACCOUNT should you heat-seal the ends of the poly strands, as this will not only look unsightly, but also cause the spliced-in natural rope to wear quickly due to friction with the sharp ends of the heated-sealed polyester. Don't even think about it!
!Fitting Polyester Ropes
Remember that you do not need to have yards of "spare" rope wound around the spokes. To do so is a waste of money. About three times round would do. If you wish to have more, extend the rope by tying some old rope onto it.
Natural fibre rope should always be used below the sally.