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Hemp strings and heavy bows

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WillS:
I've been doing a lot of research into natural fibre strings recently, and thought I'd share my (eventual) success with you guys.

I knew I wanted to use hemp, based on the small fragment found on the Mary Rose and the few historical documents mentioning hemp as bowstring material.  It's also one of the strongest natural fibres on the planet, as well as one of the longest so it makes perfect sense to use as a bowstring. 

The problem however is sourcing good quality hemp.  I've been importing hemp fibre from all over the world with little success, and finally decided to cut, ret and process my own.  I have a contact here in the UK that has an industrial hemp farm so I went over and selected my own hemp stalks to use.  They're about 3m long stem to tip.

The stalks were retted in the garden (not recommended - the smell is unbelievably awful as the cannabis plant starts to rot!) peeled the fibres from the stalks and ended up with a huge bunch of beautiful soft hemp fibre.

The fibres are twisted together in the traditional Flemish manner - a reverse-twisted three-ply laid-in top loop, no twist throughout the body of the string except to keep the fibres tight together (so no reverse-twist, essentially) and then a reverse-twisted tail in which a bowyer's knot is tied.

My requirements for these strings were fairly straightforward - they had to work with sidenocks, they had to support bows over 150lb and they had to be no larger than about 2.5mm

Eventually, after lots of failure and experimentation I hit upon the perfect glue mix for the strings - fish hide glue (not isinglass) and vegetable glycerine in a fairly high glycerine to glue ration to keep the string glue flexible. 

These pics are of the latest string, which is 2mm thick and holding nicely on a new 155lb bow that I made quickly.  The bow is nothing particularly special, it's not made to any dimensions but just roughed out by eye and feel from a piece of pale English yew.  I needed something brand new so that the brace tension was as high as possible, with a finished draw weight of 150lb+ but didn't want to spend too long on it.  I think it was just over an afternoon's work.  It's not even got a finish on it yet!  It'll probably just be a "string tester" instead of being shot, so that it's always really punchy and gives the string a full workout.

peacefullymadewarbows:
That second cow horn nock is a looker. That's really impressive. I'm not familiar with historical natural materials strings. Was it common for them to glue them? I guess I ask because other than rubbing on some beeswax we have the modern luxury of just being able to reverse twist our strings together and have them hold fast. Can the hemp not do that? Thanks for the post and that's a beautiful bow nonetheless.

WillS:
Cheers!  Well we just don't really know to be honest.  There's one document from the 17thC that suggests strings should be "gummed and not glued" presumably to avoid the brittle, hard nature of glue.  That doesn't help much however, as the word glue could have meant something different back then, and the distinction between gum and glue could simply be the addition of a plasticiser to make it more flexible. 

From the experiments that I've been conducting, it seems that if you're very lucky and get perfect fibres with no thicker or thinner areas, you can get away with just waxing the string.  However, that's extremely rare (especially today, because nobody is harvesting hemp for bowstrings so I was forced to use lesser quality stuff) and using glue homogenises the fibres into one solid item, so the areas that would otherwise be weak become as strong as the rest (within reason).

There are other documents that describe medieval bowstrings as "hard and round" which is certainly the end result of a glued string. 

If using short-fibred material such as linen however, the only way to make a string is to reverse twist everything, otherwise it all comes apart under stress.  You can either buy or make yarn or twine or cord which is all reverse-twisted - for instance Barbours 18/3 is a very common reverse-twisted yarn used for bowstrings - and pretend it's like FastFlight etc, running it end to end and just twisting up the loops, or you can reverse-twist the entire string which is what I tend to do with linen for heavy bows. 

The beauty of hemp is that it's one of the only natural plant fibres that grows beyond the length of a bow - 2m is common, and 3m is perfectly achievable.  This, coupled with its immense natural strength means you can simply peel the fibres away from the inner stalk or hurd and essentially tie it to both ends of a bow.  I've done that just as a proof of concept and had no problem with bows up to 140lb.  It's ugly and thick and very primitive but it shows the strength of hemp.  By separating the large peeled strips down into thinner sections and making nice tidy loops you end up with a very elegant solution using that natural length and strength.

(By the way, welcome to PA and I did read your Instagram message, and will get back to you with some dimensions! I've just been crazy busy at the moment and haven't had time!)

peacefullymadewarbows:
Interesting. Yeah an etymologist would be handy to have on hand to figure out that document with more assurance haha. Where I live we have stinging nettle which was used by the Native Americans for bow strings. It can get to about 1.5-2m without branching. Not soon, but once I have more patience and more experience cutting proper sidenocks (and some european cow horn for that matter haha) I'd like to try to go start to finish making a bow string for one of my 100lbers to start. So your string posts have been motivating for that.

And no worries at all! Just been very eager to go about a proper MR replica now that I'm getting the hang of making a good general heavy longbow. Your work is very appreciated and motivating. Just let me know. 

JNystrom:
Looking good Will. Now, shoot it! :)
So if the string was glued with this mixture, it wouldn't really weather proof even with wax on it. Well i don't know, wax is really good at protecting from moisture.
How does the hemp stand abrasion? Looks like you served the loops.

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