Rope, Cable, and Chain Construction

Types of rope and their characteristics

• The two most common types of rope in marine environments are polypropylene and nylon.
  • Polypropylene is a common choice because it’s cheap, durable, lightweight, and floats on water.
  • Nylon is another common choice because of its strength, abrasion resistance, how soft it is on people’s hands, and how it doesn’t degrade as fast as polypropylene in sunlight.
• Natural fiber ropes (sisal, manila, cotton) also have their applications, but due to their tendency to rot once they become wet, they’re used less frequently.  They’re usually soft on hands, but don’t possess the same strength or shock load absorption as the synthetic ropes do.  Of the natural fiber ropes, manila is the common in marine environments.
• Rope (as well as cable) is most commonly described by its diameter.  eg. 1/2″ polypropylene or 3/8″ double braided nylon.
• For a more detailed breakdown of how various ropes compare, here is a great summary in table form.

Rope construction

• The most common format for rope construction is the use of twisted strands.  Three strand polypropylene for example is a very common type of rope found in a marine environment.
• Each strand of twisted strand rope is made out of a twisted collection of fibers.
• The twisting of the strands and fibers means that the rope has a greater breaking strain than if all the fibers and strands were straight.
• Double braided rope is common as well and describes a piece of rope that has both a cover and a core made out of braided material.  Double braided nylon for example is particularly common.

Cable construction

• Wire rope or cable is woven in a similar way in that it also uses twisted strands.  Instead of fibers however, wire rope is a collection of individual wires.
• 6 strand wire rope is the most common in which 6 strands spiral around a core which is most commonly made out of fiber.
• Anti-rotating cable is another form of wire rope that is commonly used in lifting equipment.  It has incorporates both right hand lay and left hand lay strands into its construction in order to counteract twisting forces that accrue as the tension increases.
• Wire rope / cable can be galvanized and although this will add corrosion resistance to the cable, it typically comes with a reduction to the cables strength.

Lay of rope and cable

• The lay of the rope or cable refers to the direction the strands take if you were to grab a length of it and follow the rope upward.   “Regular” or “lang” laid rope refers to which direction the fibers are laid within each strand.  “Regular” means that the fibers travel in an opposite direction to that of the strands.  “Lang” means the fibers travel the same direction as the strands.
• Right regular lay (as shown in the photo) would mean the strands travel to the right as they move down the rope and the fibers travel to the left as they move down the strand.
• Regular lay is more common than lang lay because it’s less prone to kinks and pinching.  Lang lay offers more flexibility (approximately 15% depending on construction) because the lay of the fibers being the same as the strands allow the rope to stretch more as it untwists, but in doing so, tends to warp much more easily once it regains it’s shape.

Chain construction and usage

• The two main types of chain construction: common chain and stud-linked chain.  Stud linked chain has a bar through the center of the chain link while common chain does not.
• The bar through the middle of stud linked chain helps evenly distribute the load across the chain link such that it typically offers a higher breaking strain.  This bar also helps separate the areas where the links meet and helps to prevent tangling.
• Chain may be preferred to cable in specific situations because of it’s relative resistance to rust.  Cables, especially if ungreased, have a significantly larger surface area and therefore area that can be compromised by rust.
• Chain is typically used in a ship’s anchor rode and in securing buoys and mooring balls.  Whenever a line is required to spend an extended amount of time underwater and it requires a high breaking strain, chain is often used.
• Running chain under tension is especially dangerous as the links can shift and move as twists are formed or relieved.  These shifting links can easily pinch hands, gloves, or other equipment and caution should be used at all times with running chain.
• Chain is used less frequently in some applications because of it’s difficulty in being run through blocks, it’s greater tendency to damage the vessel’s paint, its noise, its weight, and its capacity to pinch once tension is applied.
• A chain that has twists in it can lead to misaligned links.  Once tension is applied to a chain with misaligned links, it can lower the chain’s effective breaking strain.
• Small pieces of chain can be useful both in securing cargo and used as a stopper for wire rope.