Ropes & Knots

Whether tethering or preparing for flight a balloon should be secured to an immovable object. The unexpected can and does happen, winds will suddenly start blowing. Like wearing a seatbelt in your car, you want to be prepared. Bill Arras' recent article (Hot Air in Antarctica, June) brings the point home. After watching a pibal go straight up for thousands of feet. his balloon is severely damaged when surprise winds hammer him during inflation. Breaking Loose on page 32 is a study on the dynamic effects of wind on a tethered balloon.

Securing a balloon during inflation or tether is usually accomplished with the use of web lines and/or ropes. This article will take a look at ropes and knots and their application to balloon operations.

Ropes can be made from many different materials; natural fiber, synthetic filaments, metal in the form of wire, or any combination. Examples of natural fiber ropes are manila, sisal, hemp, jute, cotton and flax. Natural fiber ropes are generally heavy for their given strength and are very susceptible to rot. Gas balloonists often use these types of ropes because they tend not to produce static electricity (important around hydrogen) and, because of their weight, make excellent drag lines to control the landing.

Synthetic ropes have taken the place of the natural fiber ropes for many applications. These ropes are made of Dacron, Polypropylene, and aramids, such as Kevlar. Synthetic ropes outperform their natural fiber counterparts in many ways. Besides their resistance to rot and mildew, some are very strong and have the ability to stretch and absorb high shock loads. Something that could be very important in a tether operation.

Nylon rope has become one of the most popular of the synthetics. It has very high strength and great elongation capabilities. Stumpf Ballooning Equipment in Bristol, Rhode Island sells a double-braided polyester fiber rope that is extremely flexible, easily spliced and knotted, long-wearing and tough. This half-inch rope has a tensile strength of 8,500 pounds.

The rated strength of any rope is its minimum when new. Generally a safety factor of five is applied in determining the working load on a rope. For example; if you wanted to lift 1,000 pounds with a rope a minimum 5,000 pounds breaking strength should be selected. If the load exceeds 25 percent of a rope's breaking strength, there is a good chance that it will be permanently weakened. In that case, it could fail without warning. The rated strength is based on the rope having no knots in it.

Knots or a hitch have one basic function, to hold a line secure. They also weaken the strength of the rope. The chart on this page shows approximately what percentage of a rope's strength is left after a knot is tied in it.

There are many knots designed to fulfill specific tasks. The Encyclopedia of Knots and Fancy Rope Work lists approximately 3,100 examples of knots. For a ballooning application you would like to have one or two knots that will fill the majority of your needs. In evaluating a knot to use there are several characteristics which are desirable. The "ideal" knot must: be efficient and hold secure, not slip loose; not bind under a load-therefore easy to untie; anyone must be able to untie quickly without a diagram; and the knot should be easy for most people to learn to tie.

So what knot is the best? According to David Wagoner who authored Ropes & Tether Systems, published by the Chesapeake Balloon Association in 1980, it is not the bowline. David, with many years of boating and ballooning experience, recommends a combination of a knot and a hitch.

Specifically he recommends the round turn and double half-hitch. Why does he like this combination? The round turn (not really a knot) is used to hold heavy loads in conjunction with a capstan or windlass. By holding pressure on the bitter end (the end in your hand) you can hold the load. If more holding power is needed, simply add one or more round turns. By letting go of the bitter end you can quickly release the load.

The two half-hitches are efficient in turns of strength, they can be easily tied under a load, and they will hold secure. Their only weakness is that they tend to bind under a heavy load and thus cannot easily be untied. But, combined with the round turn the combination meets all his requirements for an excellent knot. Should the double half- hitch bind, just add another round turn. Now you have a simple and effect "knot" to use in your ballooning or rope applications.

Although it is now out of print, Ropes & Tether Systems is an excellent book on basic rope, knot, and tether systems for ballooning.