Research Note

Rope walks, once again (S- and Z-twist)

John Harland

Comparing Z and S twist

With RH rope, the contlines run down and to the right when the rope is held horizontally, and although this is a useful mnemonic it does not get over the confusion that arises in trying to describe the direction in which strands are laid up. If you look directly at the end of a rope one would say the strands are twisted together counterclockwise; if you look down the length of the rope towards the end, you would say they are laid up clockwise. To avoid ambiguity it is usual to say rope is Z-twist (RH) or S-twist (LH). To see why hold a length of rope vertically.

The modeler does make his rope in the same fashion as in a full size ropeworks. The essential feature in construction a rope is the reversal of twist at each stage to prevent unravelling. Thus Z-twist yarns are spun into S-twist strands, which are laid up to make a Z-twist rope. If three of these are 'closed' left-handedly, we have an S-twist cable.

The modeler will be content with a one-stage process, and hence virtually all thread purchased will be made of Z-twist yarns, it will be actually be more practical for the modeler to make S-twist or LH rope! The difficulty with this is that almost all rope used to outfit and rig the prototypes of our models was Z-twist! The reason for this is uncertain, and the major exception to the rule was of course cable-laid rope, made of three Z-twist rope, and used for cables, messengers, larger sizes of stays and shrouds. In smaller sizes S-twist was used for leadlines and gun-gear including breeching ropes, but in this case since both yarns and strands were Z-wist and the product was less stable.

Nor need the modeler trouble himself with shroud-laid rope ( four strands and a heart) ...the observer cannot distinguish this from three-strand rope.
{John Harland}

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