Fast Flight Strings and the Bowyer's Knot: a Solution from Japan

A while back, I wrote a blog post on the utility of the bowyer's knot in the bow making process. One important aspect I left out of that post was the importance of string material to the function of the boywer's knot.  The reliability of the bowyer's knot is dependent on the material of the string.  While the bowyer's knot, aka timber hitch, holds securely on the rawhide, hemp, linen, sinew, and even Dacron B50 (polyester) strings, it has a tendency to pull out when used on the modern low stretch string materials, such as Fast Flight (kevlar). This can be frustrating, as the low-stretch material is well-suited to the task of tillering, while material such as B-50 is not.  Anyone who has experienced making a long-string from B-50 only to have a reflexed bow of decent weight stretch all of the brace out of the string knows that there has to be a better material for tillering strings. Likewise, the bowyer who has a fast flight string slip its bowyer's knot while under tension on the tillering tree wants for a way to make it work. Well, it appears the solution comes from Japan and the practice of Kyud: Japanese Archery.

I had recently cut a very long stave of vine maple (Acer circinatum). It had very nice reflex that began to really show itself after sawing the mature vine maple trunk in half along its length. This reflex was balanced near a point favoring the lower limb. Its form immediately brought to mind the Yumi bows of Japanese Archery. The Yumi bow is traditionally constructed of a bamboo belly and back with a bamboo and mulberry laminated core, but the idea of making a vine maple self bow in the yumi form had captured my imagination. I started in on reaserching the finer details of the Yumi's construction, and that is when I stumbled upon the solution.

The Tsuru, or Yumi bow-string, incorporates an adjustable lower loop (Tsuruwa?) that struck me as simply a "double bowyer's knot". This simple variation on the handy western knot looked like it might be the ticket for utilizing the low-stretch Fast Flight string material in an adjustable tillering string. I have since given it some testing on Fast Flight Plus string material, and so far, the knot holds. This, in my opinion, is huge; to utilize an adjustable knot with the low-stretch kevlar based string materials, such as Fast Flight Plus, is to remove the fuss and finagling from tillering strings.  It is the small discoveries, such as this, that I find exciting enough to write a blog about. I hope the information is shared widely enough that green bowyer's everywhere will not have to experience the frustration of having an adjustable Fast Flight tillering string fail at the knot on them.

Figure 1.  A traditional Yumi bow shown here unstrung (top) and strung (bottom). Note the extreme amount of reflex and the handle position well below center.

The knot itself is quite basic. It is a simple modification on the well-known bowyer's knot (aka timber hitch). The tsuru knot differs only from the bowyer's knot in that it incorporates two wraps around the body of the string, as opposed to one in the bowyer's knot, hence the name "double bowyers knot". This doubling-up appears to be all that it is needed to make the knot hold on "slick" materials such as Fast Flight.

Figure 2.  The tsuru knot, an adjustable bow string knot from Japanese Archery, Kyudu. The solution to the bowyer's knot and issues of slippage with kevlar based string materials. 

 At this point, I have only tested it on a couple of bows and only one of the modern kevlar based string materials and that is Fast Flight Plus in a 12 strand (2 bundles of 6) string.  Based on the performance of the tsuru or "double bowyer's knot" with this material, my feeling is that this knot will hold on any of the variations of modern low-stretch string materials. If you find that not to be the case, please let me know in the comments.

Best of luck in bending wood this holiday season!
Carson
Echo Archery
http://echoarchery.com/bow-strings