Rigging is the system of ropes, wires and chains used to support and operate the masts, sails, booms and yards of a ship. It is also useful for moving heavy cargo aboard and around a pirate ship.
Rigging is used to attach the sails to the mast and yardarms of the sailing vessel to catch the wind and increase sailing speed; this is extremely important for a pirate ship. The event cache was a knot puzzle to find the coordinates, but this is being published as a traditional cache. Here is a fun link to learn new knots!
https://www.instructables.com/id/Knots/