... has nothing to do with the legal system. (I always thought it did!) In a brief hunt to find out if "rigging" was used as a verb as well as a noun, I found this (from Wikipedia):

On sailing ships, the jury rig is a replacement mast and yards improvised in case of loss of the original mast.

There are these theories about the origin of the term "jury" in this sense:

• A Latin and Old French root meaning "aid" or "succour".
• "jury-mast" derived from "injury-mast".
• From French du jour = "of the day", thus `temporary'.

While ships typically carried a number of spare spars such as topmasts, the lower masts, at up to one meter in diameter, were too large to carry spares. So a jury mast could be various things. Contemporary drawings and paintings show a wide variety of jury rigs, attesting to the creativity of sailors faced with the need to save their ships. ...