Shortly before it’s rupture, after being inadvertently dry-fired during our last field trip, the port limb  (seen on the right in the photo below) demonstrates a tad more curvature at full draw than it’s companion on the other side.

It’s likely that slight  differences in the grain structure of the two pieces of ash effected the relative stiffness of each limb.  Tillering the limbs, as is common in regular bowmaking, is not really a practical venture in ballista making.  It would  undoubtedly be better to devise a scheme that simply raised the stiffness of both the limbs.  This is not so easy if you are trying to keep the weight down, while still presenting a historically authentic plan.  Clearly, the Dacron material in the tension backings presented here is far from authentic, but as an analog for sinew or flax in a composite type construction, it is not completely without merit.  Similarly, we might regard these Dacron backings as prototypes for ones made from thin strips of spring steel; a material that would most certainly pass the authenticity test.

A plan comes to mind where a wooden spacer could be inserted under the middle of the tension band to raise it away from the surface of the limb.  This would redirect some of the forces back into the center of the limb and stiffen it with a minimum weight penalty.  This would be similar to the design  concept of the ancient cable-backed bow.

The better route that we seek is not always a neatly disposed, straight line.   Meandering baby steps can sometimes be turned into real leaps forward.  At least, so we tell ourselves halfway out of that hole we stumbled into last week.

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