Think about it. After making a knot, what’s the last thing you do to ensure it will stay put? You give it a sharp tug. Fair enough, but why does a tug keep a knot from unraveling?
The answer is friction, something when two or more surfaces are in contact with one another and creating a force, or potential force, that is opposing any attempt to move them. Friction can be also described using the equation Ff = μN, in which the amount of friction (Ff) is equal to the coefficient of friction (μ, basically a “stickiness factor”) multiplied by the force with which two surfaces are being pressed together, referred to as the normal force (N). In layman’s terms, by giving a knot a quick tug you are squeezing the parts of the knot together, which bumps up the normal force. This, in turn, cranks up the friction wherever the rope is in contact with itself so that the knot won’t slip apart again.
The most useful sailing knots were created with a release mechanism a lever. The idea is that knots should be as easy to take apart as they are to tie in the first place, no matter how hard or how long they’ve been at work.
Researchers figured out ways to create inexpensive, effective, synthetic substitutes in the early twentieth century. The first of these, nylon, was discovered in 1935 by American chemist Wallace Hume Carothers, who worked for DuPont. Nylon is strong, abrasion-resistant. It’s also stretchy, which makes it an especially good material for anchor rodes and mooring lines. In fact, most of the three-strand ropes manufactured today is made of nylon, specifically for these two purposes. Under load, nylon can safely stretch up to 20 percent of its length which goes a long way toward decreasing the shock loads on a vessel’s foredeck cleat when it’s tugging at its dock ropes in a blow.
Polyester or Dacron provides approximately the same tensile strength as the nylon, but without all these tensions. It is also abrasion-resistant and absorbs very little water. Polyester has been an almost universal workforce in the sailing community for decades, where it is used for everything from halyards to sheets and smaller control ropes.
Polypropylene, like nylon, is flexible, but only half as strong. Even worse, when exposed to ultraviolet light, it hardens and deteriorates over time, not suitable for use on a sailboat.
In addition to the advantages of strength and durability, synthetic fibers can be made in unlimited lengths they offer. Alternatively, even if it is a fairly long single polyester or nylon fiber, it can stretch the entire length of the longest halyard. Need to cover the fibers with a loose, soft, and easy-to-use thread.
In addition to nylon, polyester, and polypropylene there are several “miracle” materials on the market today, whose strengths and weaknesses are worth reviewing. Kevlar for example is substantially stronger than nylon and polyester. It also provides minimal stretch. On the downside, it tends to absorb water and is susceptible to damage from ultraviolet light a problem for those who like to go sailing during the day! Kevlar also tends to break down when subjected to repeated bending a problem given all those pesky blocks and cleats on a sailboat. For these reasons, rope makers rarely use Kevlar anymore, although it’s still used in some high-performance sails.
Ultrahigh molecular weight polyethylene (UHMWPE) which goes by a number of names, including high-modulus polyethylene, Dyneema and Spectra are also extremely strong and stretch resistant. Single-braid 6 mm Dyneema line, for example, has a breaking strength of nearly four tons! Ropes made from this material are more workable than Kevlar is not absorb water and are less vulnerable to ultraviolet radiation. On the downside, UHMWPE has a low μ factor, which makes it slippery, with poor knot-holding ability. It’s also subject to creep it slowly elongates overtime under a heavy load and then stays that way. Technora is strong, low-stretch, and unaffected by creep. However, it doesn’t take well to bending and is sensitive to ultraviolet light. Technora is often encased in a polyester sheath and blended with other fibers (such as Spectra) to minimize its weaknesses, allowing rope makers to take advantage of its strength.
Vectran produces ropes that are strong, extremely low-stretch, water and UV resistant, durable and unaffected by creep. A 6 mm single braid fabricated from this stuff has a breaking strength of around seventy-five hundred pounds. The only downside is the price tag! Ultimately polyester and nylon are more than adequate for the vast majority of applications afloat. They may not be the latest miracle fibers on the dock, but they’re miracles of modern chemistry. If you ever reach a point in your sailing where you need to spend an arm and a leg on the latest miracle sailing rope, you’ll know it.
Modern Synthetic Fibers
Advantages: Strong and stretchy, making it useful for dock lines and anchor rodes
Disadvantages: Absorbs water; loses some strength when wet
Advantages: Strong, low-stretch, abrasion-resistant and water-resistant
Disadvantages: There really aren’t any. There’s a reason Dacron line is ubiquitous
Advantages: It is one outstanding quality is that it floats
Disadvantages: Relatively weak and stretchy; breaks down over time in sunlight; is hard on the hands
Advantages: Very strong with minimum stretch
Disadvantages: Absorbs water and breaks down in sunlight; breaks down after repeated bending
Ultrahigh molecular weight polyethylene (Dyneema and Spectra)
Advantages: Extremely strong and stretch resistant; doesn’t absorb water; does well even in direct sunlight
Disadvantages: Susceptible to creep
Advantages: Very strong, low-stretch and unaffected by creep
Disadvantages: Sensitive to sunlight; doesn’t take repeated bending well
Advantages: Extremely strong and stretch resistant; durable and unaffected by water or sun
Disadvantages: High price.
The Most Useful Sailing Knots
Tying and Untying a Bowline
To make a bowline, first loop the rope in a counterclockwise direction laying the bitter end across the standing part of the line. Next, thread the bitter end up through the overhand loop you just created making sure there’s enough line in the loop you’re creating to serve the knot’s purpose. Then pass the bitter end behind the standing part of the line and snug things tight.
The Figure Eight Knot
Take the figure-eight sailing knot, which is used as a stopper to keep the end of a line from running through a block or halyard clutch. In contrast to a simple overhand knot, the bight that curves around the standing part of the line provides a release mechanism similar to the bowline’s life preserver: pull the bight up and over the standing end, and you turn off the friction machine. Try taking apart an overhand knot after it’s been given a good tug.
The Square Knot
It’s the same thing with the square sailing knot. In this case, you have two bights to work with. Granted, there isn’t the same magical release that comes with breaking the life preserver on a bowline, but it works.
Note that the square knot or reef knot is also called due to the fact that it is an excellent knot for tying together sail ties when shortening sail is only supposed to serve as a temporary knot and is not especially secure. Therefore it should never be relied on for either joining ropes that will be under heavy load or joining two ropes of different diameters.