I wondered what sort of weight would be expected from the tip fragment that was found near the tiller. First I built an elm bow but I went much too short and didn't deal correctly with a row of pin knots that crossed on limb. I saw over 100lb but then had to scrap the bow as the knots began to fail.
I have had another go with a better piece of elm, going slightly longer at 95cm tip to tip, including the recurves - 89cm working length - working backwards from the tip, tracing a correctly sized tip drawing of the tip and extending the bend the tip dimensions produced backwards to the centre. I also experimented with making the proper recurves. The work was very revealing about why the tips are the shape they are (the triangular end is perfect for hanging a stringer on) but the bow was only 65lb. I reckon a better bowyer should get a few extra pounds from it, maybe 80 to 100lb is reasonable. Don't forget the bow is slightly stronger than it feels as the recurve levers will have an effect but they are very short, so the effect will be limited.
I'm going to try again and see where I end up.