Jury rigging (also Jerry Rigging) refers to makeshift repairs or temporary contrivances, made with only the tools and materials that happen to be on hand. Originally a nautical term, on sailing ships a jury rig is a replacement mast and yards improvised in case of damage or loss of the original mast. While ships typically carried a number of spare parts (e.g., items 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. Ships always carried a variety of spare sails, so rigging the jury mast once erected was mostly a matter of selecting appropriate size. 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. Example jury-rig configurations are:
- A spare topmast
- The main boom of a brig
- To replace the foremast with the mizzenmast: mentioned in W. Brady's The Kedge Anchor (1852)
- The bowsprit set upright and tied to the stump of the original mast.
The jury mast knot is often mentioned as a method to provide the anchor points for securing makeshift stays and shrouds to the new mast. However, there is a lack of hard evidence regarding the knot's actual historical use.
Although ships were observed to perform reasonably well under jury rig, the rig was quite a bit weaker than the original, and the ship's first priority was normally to steer for the nearest friendly port and get replacement masts.