Weak Links and Leader Lines

Weak links are one of the most important safety features that can be applied to tow launched flight. There are arguments for and against their use, but the most compelling arguments are for their obvious safety benefit.

A weaklink acts primarily as a safety fuse to prevent overloads from being applied to the towed pilot. Under ideal circumstances, the tow operator could foresee every possible development that could occur and react instantaneously to prevent any type of overload from occurring. The real world doesn't work that way. Lines jam, skip off pulleys, get run over by other vehicles or animals, tension control systems fail, operators and pilots alike make mistakes, and meteorological conditions conspire to occasionally overload the system. A properly designed weaklink will blow out before any excessive forces can be transmitted to the pilot or their glider. One weaklink does not work for all pilots. Most reliable sources believe that a weaklink should be sized so that it breaks at 75% to 100% of the inflight load. Light pilots need weaklinks that break with a lower force than heavy solo or tandem pilots. Wrapping a shoelace and tying a knot is perhaps better than nothing, but very few pilots actually have any idea at what force their links will break. Tying a weaklink has always been the way most people get by. But when you take some 200 pound test line and tie a knot, at what force does the link break? Different knots, how the knot is tied, and even the length of the line used to tie the knot greatly affect how the link will break.

Sewn Weak Links - To ensure consistent breaking strengths, at TowMeUp.com for our own personal use, we used to use individually sewn and calibrated weak links. All our links were the exact same size and can be combined together to vary the total force required to break the link. We used to offer them for sale, but the demand far exceeded our ability to produce them economically. We do, however, offer the precut and marked line for those who choose to sew their own. The same precut links also work well when tied using the double grapevine knot, and we have found that a properly tied knot produces a weaklink that breaks with great consistency. It's possible though that the accuracy varies by +/- 10% or so of a calibrated value depending on how accurately the knot is tied and cinched together.

Tied Weak Links - If you are unsure how to tie your own weaklinks, we have provided an informational page on how to tie your own weaklinks, as well as a page on how to build your own weak link tester to calibrate their breaking strength.

THERE IS A HUGE MISCONCEPTION IN THE PILOT COMMUNITY RELATED TO HOW STRONG A TIED WEAKLINK ACTUALLY IS IN PRACTISE! KNOWING WHAT LOAD YOUR WEAKLINKS WILL WITHSTAND BEFORE THEY BLOW OUT IS CRITICAL TO FLIGHT SAFETY. A WEAKLINK THAT BLOWS OUT PREMATURELY CAN IN MANY CASES BE WORSE THAN USING NO WEAK LINK AT ALL!

A popular misconception uses a very common 135 pound test green spot trolling line. In fact the myths associated with this product are so strong we no longer carry it. If you wish to obtain some, it can be easily found at any decent fishing store as Dacron Trolling Line made by the Green Spot company. Here's how the myth goes - Look at the knot tied link shown in the picture above. Many, many pilots believe that if you take a 135 pound weaklink line and tie it in a loop that it will break at 270 pounds. The logic is that there are 2 parallel load paths sharing the load, each one capable of withstanding 135 pounds. They miss the fact that any properly tied weaklink will ALWAYS fail at the knot. The line is pulled tighter and tighter at the knot and should break right at the knot every time. Depending on the knot used the line will break at 40-60% of its rated strength. Typically a weaklink tied with a double grapevine will break at slightly over the rated strength of the line. The only way to tell for sure is to break test it with a calibrated tester. There have been many inadvertant weak link breaks caused simply because pilots ASSUMED that the link was stronger than it was. This has led to the asinine belief that if one loop is good 2, 3, or 4 is even better.

In use the weaklink material will stretch well over 60% in length before it fails at the knot. Adding a multitude of loops makes it impossible to spread the load evenly, and the link will likely bind up causing it to fail in an often unpredictable and unrepeatable manner. To ensure consistent breaking strengths, stacking equal length weaklinks works, using a single appropriate strength link is the best, and multiple wraps should never be used.

We currently stock pre-cut and marked weak link line in 150, 200, 250, and 300 pound breaking strengths.

150 pound test (white with a blue striker)

200 pound test (white with an olive drab striker)

250 pound test (white with a red striker)

300 pound test (white with a black striker)

If you happen to tow with us on one of our towboats, you would notice we almost always have a pair of links tied from 250 pound test line and another from 300 pound test line. The smaller links break at around 264 pounds and are used by almost all solo pilots. The larger link breaks at around 384 pounds and is used for tandems. The links are all the same length when tied which we use to tell if a link has had a transient overload applied. Lets say on the previous tow the pilot had an overload situation occur that dramatically stretched the link, but didn't cause it to blow out. This will be obvious when the next pilot is hooked up for the tow, as the overloaded link will be an inch or 2 longer than the others. We simply cut it off, use the other link for the tow, and replace the link when the drogue is rewound for the next tow.

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Leader Lines are typically short lengths of spectra with sewn eyes on both ends. Typically they are connected between the apex of the drogue chute and the weaklink clip in link. Leader lines serve 2 functions. Primarily they are used to add space between the drogue chute and the pilot. In the event that tow tension is reduced in flight, the drogue chute will inflate. The use of a leader line ensures this happens well in front to the pilot, rather than in the pilots face. We typically use a leader line of lower breaking strength than the towline and use it as a "backup" weaklink for those applications where a pilot elects not to use any type of safety link. Our sewn leader lines are available in 6 - 8 foot lengths in the following breaking strengths. 825 Lb., and 1800Lb breaking strengths.

Costs

All strengths of sewn weaklinks cost the same, please specify the quantity and breaking strengths desired.

Packages of 10 pre cut and marked 20" cords to be tied or sewn into weaklinks (any size) sell for $ 2.30

Packages of 60 pre cut and marked 20" cords to be tied or sewn into weaklinks (any size) sell for $ 13.20

You may mix and match breaking strengths to meet the quantity pricing structure.

For small or large quantities of line please contact us with your request and a custom price quote.

Leader lines sell for $6.50 - $8.50 depending on size and length. Contact us for pricing, and quantity pricing.