So Many Different Ropes - Need a Little Help Choosing?
Samson offers 20 different ropes specifically for use as running rigging. Each is engineered to perform superbly under a particular set of circumstances. The choice may seem intimidating. Armed with a little knowledge, an accurate assessment of your sailing needs, and what you expect from your lines, the choice becomes clear.
Accurately Assess Your Working Load
Selecting a rope begins with an accurate assessment of the loads it will encounter. Formulas for sheet loads are available, but consider the following:
- Halyard loads are best determined by your rigger. For sheets, halyards, or control lines, anticipated loads are considered working loads. The standard working load for any Samson rope is 20% of the rated break strength.
- For example, the total load for an end-of-boom mainsheet going through a four-purchase sheave system may be calculated at 900 lbs. Factoring in a 20% working load, the rope’s break strength needs to be five times the working load, or 4,500 lbs. for this application.
Synthetic Fibers: What are the Differences?
Nylon was the first synthetic fiber widely used in ropes. Reasonably strong (much stronger than the natural fibers it replaced), nylon is still used in dock and anchor lines where its excellent elasticity allows it to absorb shock loads. But for many sailing applications, elasticity is not a desirable trait.
The introduction of polyester fiber allowed rope manufacturers to build ropes that were as strong as nylon, but with much less stretch, less wet-strength loss, and a higher coefficient of friction. Because it has excellent grip, it works well on winches. Polyester ropes, particularly polyester double braids, became the standard against which all ropes were measured. Polyester is still regarded as an excellent fiber for many marine applications and is widely used for covers on high-performance, or high-modulus double braids.
High-modulus Fibers: Which one, for What Purpose, and Why?
There are several modern high-modulus fibers, each with a unique set of characteristics. The challenge of the rope designer is to match these characteristics with the unique performance requirements of the application for which they are designing.
Dyneema® is a high modulus polyethylene (HMPE) fiber with a particularly well balanced set of characteristics that allow it to be used in a variety of applications. Extremely lightweight (1/7th that of steel) with ultra-high strength (at least as strong as steel wire at the same size), very low stretch, and excellent abrasion, cut, and UV resistance, it is well-suited for use in halyards, control lines, and sheets.
Within the Dyneema® family of HMPE fibers are several grades, each possessing different characteristics that include increasing levels of tenacity, durability, and resistance to creep. Samson uses Dyneema® fiber or Dyneema®-fiber blends in more than half of the lines that comprise the competition-grade running rigging.
Other high-modulus fibers include Technora®, an aramid fiber that blends very high strength, low stretch, and abrasion resistance with extreme heat resistance; Vectran®, a liquid crystal polymer (LCP) fiber that has very high strength and very good heat resistance; and Zylon®, or PBO fiber, which offers the highest strength of all the high-modulus fibers; but it must be protected from UV light. Technora®, Vectran®, and Zylon® are all exceptionally low-creep fibers.
In some cases, Samson blends fibers to take advantage of the relative properties of each of the components. Lightning Rope is a good example: the lightweight characteristic of Dyneema® fiber is blended with the strength and exceptionally low-creep characteristics of Vectran® fiber. The result is a rope that is lighter than Validator-12, an all Vectran® 12-strand, while sacrificing only 5% of the strength of AmSteel®-Blue, an all Dyneema®-fiber 12-strand line.