Understanding the Strength and Composition of Bowstrings
Strong AF. While at Fort Hood, we experienced the archery range with 80lb draw compound bows, capable of doing anything you want.
Strength is crucial for a bowstring, but it needs to possess additional desirable qualities such as resistance to abrasion, water resistance, and low stretch.
While Dacron is still a popular choice, modern low stretch, high strength materials like Dyneema are widely used.
Consider a recurve bow with a 50 lb draw weight. The upper and lower parts of the string each take up half of the pull. If the angle they make with the arrow at full draw is 45 degrees, then the tension in each part would be 25x√2, which is approximately 35.35 pounds. The total tension is twice that, or 70 pounds. However, the string is also under tension just from being strung, and this tension is estimated to be around 25 pounds. Therefore, the total string tension is 95 pounds.
To ensure safety, we'd want a safety factor of 1.5, meaning the string should be able to stand a pull of 143 pounds.
Note: This number may need retesting, so it should be taken with a sizable dose of salt.
What Kind of Bowstring?
The choice between natural and synthetic materials is always changing and can be hard to keep up with. For example, with modern synthetic materials, a 12-14 strand B50/55 Dacron sting is recommended for a bow, as it has 50/55 lbs per strand strength, totaling 600-750 lbs. A 16-18 strand Fast Flight FF string, while heavier at 1520-1710 lbs, is often preferred for better nock to string fit and may be thinner per strand.
A modern 18 strand FF string is sufficient for the heaviest English Longbow. I recall that Mark Stretton used such a string for his 200 lb draw longbow record.
Modern strings are much thinner and stronger than natural materials, which were thicker. This explains why older relic arrows have larger nock openings than modern arrows.
Strength Requirements for Different Draw Weights
A flax string on a full power longbow with about 150 lbs of draw weight must have been rather heavy. However, it's reasonable to assume that a decent archer would have been well-paid and could find silk in France, reminiscent of the historical accounts. Silk was used to make bowstrings, as excessive royal heirs were strangled with a silk bowstring in the Constantinople. These bows, which had similar pulls of up to 180 lbs, are known to have sent arrows beyond 500 meters.
Thus, the strength and composition of bowstrings play a critical role in the effectiveness of a bow, and understanding these factors can enhance your archery experience and performance.