Parrel

Parrel, also known as a parrel bead or truck, is a device used in sailing to allow a square sail to slide freely along the mast or spar. It consists of a series of beads or rings, typically made of wood or plastic, strung together and attached to the sail's bolt rope. These beads encircle the mast or spar, preventing the sail from binding and allowing it to be raised and lowered easily.

The primary function of parrels is to reduce friction. As the sail is hoisted or lowered, or when the wind shifts, the sail needs to move up and down the mast. Without parrels, the rough surface of the sail rubbing directly against the mast would create significant resistance, making these movements difficult and potentially damaging the sail or mast. The parrel beads roll against the mast, acting like a rudimentary bearing system.

Parrels are particularly important on ships with multiple square sails. Each sail typically has its own set of parrels. The number and size of the parrel beads can vary depending on the size of the sail and the mast. Older sailing vessels often used wooden beads, while modern applications may employ synthetic materials for increased durability and smoother operation. The design ensures that the sail can be easily reefed (reduced in size) by allowing the upper portion to be gathered and secured.