Some years ago, my sport of choice was Archery and on one occasion I had an opportunity to use a real Longbow. The Longbow is a reasonably light weapon and seeing a Longbow archer string it and draw it, you would have thought it would be much like stringing and drawing a modern compound reflex bow. Sadly to say, I was not man enough to handle a Longbow, even though I had been shooting a 42lb bow in competition for a few years. I could not even flex the bow staff sufficiently to string it, let alone draw the brute. The staff was rated at 80lb at 30" draw, yet it must have sustained nearly that weight just to bend the staff sufficient to string it. When the bow had finished throwing the arrow forward, the shock wave running through the string as the staff ends suddenly met a straight cord with no means to give any further, caused a resounding and characteristic ‘bang’. The residual forces taken by the bowstring must be enormous and way in excess of the ‘puny’ 80lb held on the archers fingertips.
The bowstring was made with a loop preformed in one end. The archer then had to tie the second end loop at the point which would give his exact draw length for that particular bow staff. Although Ashley shows a number of ‘Bowstring Knots’, none resemble the knot we were taught to make, which was simply a tucked overhand knot making a slipped loop. The end was then simply passed around the back of the bowstring and then back through the centre of the overhand knot emerging in the middle of the loop. The bow staff was bent to the desired curve and the loop offered up to the horn notch. The loop was then adjusted to length by pulling excess loop back through the overhand knot, then a little tension was allowed to be placed on the OH knot to tighten it while holding the sliding end. The excess slack was then drawn through the middle of the OH knot to lock the loop length. The full weight of the bowstaff was then allowed to be taken by the string. Last minute adjustments in length can still be made using a spike to prise out the end before setting the knot in place for good by shooting the bow. Very heavy arrows can be used for the first shots to dull the residual force hitting the string at the end of the shot. After the first shot the knot will have lost virtually every identity except where the cords enter and exit the rock hard blob that was once an identifiable knot.
Today, modern bowstrings are made exactly to length by winding a single strand of 100lb Spectra (or equivalent) repeatedly around two pegs fixed the required distance apart. The end loops are then formed into eyes and whipped for shape and wear protection. The bulk of the bowstring is left as free strands except for the centre section used to take the arrow knock, this is also whipped to give a thickness to grip the knock and to give a solid holding bed for the three bow fingers to bear on the string and a smooth section to roll off the fingertips in the loose. Unsurprisingly modern bowstrings never break and have no weak knots to fail.
It is only recently that I have given any thought to the bowstring knot and in particular its strength. I have stood at the target butts when arrows hurled from 100lb bows came scything in, that sound touches a very primitive fear chord. The sound at Agincourt must have briefly chilled the hearts of the Frenchmen before permanently stilling them. The force imparted to the arrow is huge, the residual force left hitting the bowstring knot as the string finally hits straight is likewise enormous. Yet the knot which won wars and made nations, is little more than the tucked overhand knot - where have I read that the overhand knot is amongst the weakest? reducing the cord strength to ca 50%. Did we really take our best bowstaves and our strongest bowstring, then finish them with one of the weakest of all knots, or does this little knot which must have seen millions of impacts (and survived) perform far better than we might give it credit?
The bowstring knot has seen such extreme use, I remain certain that if the knot was in any way lacking it would have been fast replaced by a better (i.e. stronger) knot. So just how strong is this knot?
The Slipped Overhand Knot
http://igkt.pbwiki.com/f/Slipped-Overhand.gif
The Bowstring Knot
http://igkt.pbwiki.com/f/Bowstring-Knot.gif
The dressed knot front and back
http://igkt.pbwiki.com/f/Bowstring-Knot-F-B.gif
The Overs Index {OI-9:12}
Note the saturation is counted with the loop included as part of the knot.