Making rope for ship model rigging
By David Nelson
In order to have properly laid up, properly scaled rope for your ship model you will in all probability have to make it yourself. Most model rope on the open market is just string and in limited sizes. Even line supplied with kits is not properly laid up and not provided in all of the sizes required to properly rig the model.
This article will discuss the physics of making rope, ways rope is treated to meet the stresses induced on an operating vessel, and how to make the rope.
The physics of it:
The rope is typically made up from three strands of yarn. For a model linen, cotton or synthetic fiber can be used.
To form the rope the natural twist of each strand is increased under tension to the point that they twist around themselves and against their neighbours, thus forming the rope. However, the extra twist put into the strands is not all removed when the rope forms, and the tendency of the strands to return to their original state tightens the twist in the rope and holds it together.
The diameter of a three strand rope will be about twice the diameter of a single strand.
You can test the theory of a strand twisted under tension and forming a rope by holding a piece of yarn between two hands, pull it tight then significantly increase the natural twist of the yarn. If you release the tension now the yarn will twist onto itself forming a two strand rope.
Very heavy lines such as those used for shrouds and anchors are called cables. A cable is made up of three or more ropes using the same technique used to make rope, but in this case the added twist is applied to the ropes in the opposite direction to that used with the strands.
Treatment of rope to protect it.
Some portions of the rigging of a sailing vessel, particularly the standing rigging, are subjected to abrasion and other stresses such as are caused by long exposure to salt water. To protect the rope one or more of the following techniques was employed.
Worming: is the application of a small line into the groove between strands of the rope to make a smooth surface.
Parceling: is wrapping a layer of canvas over the rope to protect it from abrasion. This is not relevant to a model as it makes the line look too bulky.
Serving: is applied to lines such as shrouds and anchor cables which receive high levels of abrasion. A small line is tightly wrapped around the wormed rope or cable in the sections subject to abrasion.
Making the rope
Modern rope making machines are automated and can produce very long lengths of rope in various sizes which makes them quite complex. Until the invention of these automate machines and for the model builder a rope walk is used.
There are many variations of rope walks but this diagram shows the components that must be there.
Three strands are fastened to the hooks in the gears on the right. These gears are rotated by a motor or crank in a direction that adds twist to the strands.
The weighted unit on the left keeps tension on the strands and resulting rope. This unit must be able to slide because the length of the strands will decrease as it is twisted and as the rope forms. The swivel at the front of the unit allows the rope to turn as it forms.
The shuttle in the middle keeps the strands separated until there is sufficient twist in the strands to form the rope. As the rope forms the shuttle will move to the right. The rate at which the shuttle moves will determine the twist of the rope which is referred to as turns per inch. To produce a properly laid up rope the turns per inch is higher for small lines than the larger ones. Independent of the size of rope being made it should look like that in the diagram on page one.
The length of rope that can be produced this way is less than the maximum distance the gear drive and weighted unit are apart when the process starts.
Example of an automated rope making machine
Without going into a lot of detail about how the machine works we can see the basics are there. The bobbins on the right hold the strands, keep them under tension and apply the twist required to form the rope. The cone in the center is where the rope forms. The flier on the left spins to form the rope. In this flier are capstans to pull the rope through at the required rate to achieve the proper turns per inch, and a take-up bobbin to contain the finished rope.
This machine produces rope in twelve diameters from 0.010” to 0.120” and is controlled by a timer so once it is set up it can run without manual intervention.
Modern rope making machines use the same basic design.
Modern braided rope is made from synthetic fibres on machines of a totally different design principle, but such ropes of course did not exist it the days of “period” ships.
Happy model building.