Windsurf mast
A windsurf mast serves a similar purpose to all other sailing masts, it’s the vertical attachment for a sail. The masts used to be little more than poles that fit into an indentation in a windsurfing board, but with the advent of more outrageous maneuvers and higher stresses on a windsurfing rig, they have been firmly attached to the board via a freely rotating universal joint, or u-joint.
In addition to attaching to the sail and the board, the windsurfing mast serves as an attachment point for the boom. The boom allows a windsurfer to rotate the mast on the u-joint to tack into the wind or perform tricks. The boom clamps on to the mast to ensure a tight fit. Between the attachment to the mast and boom, a sail is kept relatively taut regardless of wind conditions during windsurfing.
Perhaps the most underrated use for a mast is as the attachment point for your harness. The windsurfing harness allows you to support your body weight with your torso, rather than your arms. This allows your arms to be free to maneuver the sail and your craft, and lightens the load they will bear. Additionally, the harness will keep you and your board together if you should crash while windsurfing. This keeps you from losing a few thousand dollars to the current, a remarkably handy thing to do.