The suitable rope for the right application is crucial to optimum performance. Twisted cotton ropes have a wide range of applications and can be used in almost anything from industrial, commercial, and consumer uses.
The average breaking strength of a twisted cotton rope is typically about 15–20 pounds per square inch (PSI) when new or freshly broken in. It is much lower than other standard ropes like nylon and polyester blend climbing ropes, which average a PSI strength of 80+. When buying this type of rope, here are the features and factors to consider:
The diameter of the rope is a key factor in determining what applications it can be used for and how many falls are allowable.
The thinner the rope, the less PSI or weight it can handle. The thicker or heavier the line, the more is the PSI capacity. Twisted cotton ropes are available in diameters from 1/8 inch to 1 inch, and larger sizes can be specially ordered.
The tensile strength is the weight a twisted cotton rope can hold before breaking. As a rope is weighed with a load, it accumulates stress at specific points. If your line is strong enough to hold the weight given, then the forces will spread out evenly across the length of the material. If not, the rope will eventually break.
The breaking strength of 15–20 pounds PSI of twisted cotton ropes can be increased if the fibers are scoured by sanding up to 25% of the material away.
There are several areas of concern for abrasion. The first is conditions on the ground or floor where your rope is being walked on. Next, the line’s storage and use environment include the rigging hardware. Finally, there are new environmental concerns of marine life ingesting your line after being in the water.
If you’re tying yourself off to an anchor frequently, make sure your rope is long enough and can easily hold your weight (plus gear). A good rule of thumb is at least four feet longer than your height – if you’re six feet tall, then get a ten-footer. Thus, if you’re climbing in extremely cold or wet conditions, your line may need to be longer than your body height.
Extreme heat can also cause problems with cotton ropes – the fibers collapse together when they get too warm, which reduces their strength considerably at those times.
If you need a cotton sling to serve as a makeshift climbing line, make sure it’s not older than a year and always replace it when you do overhaul your gear.
Other Attributes of Twisted Cotton Ropes
Besides tensile strength, several other factors evaluate how strong a given cotton line is. These include the number of twists in the strands, the number of plies (strands twisted together), and the total length of the line.
Higher-quality ropes generally have more twists per inch than lower-quality ones, but this doesn’t guarantee that they’ll be any stronger. More importantly, higher weave counts and longer lines equate to a lot less wear and tear on the individual strands, which results in a longer lifespan for your rope.