A windsurf mast foot is the area of the board that houses the bottom end of the universal joint which attaches the mast to the board. initially, the mast foot was just a depression in the board where a surfer could set the mast. In the first windsurfing setups, the mast and sail were actually a completely separate piece which wasn’t attached to board itself. The surfer would hold the mast in place to let the wind help the surfer.
It almost does not need to be said that the sail was not very effective used like that. The wind seems like a flimsy thing, but the force it can apply to 30 square feet of sail is easily more than the average human can resist comfortably while standing upright. That is why the windsurf mast foot moved from a depression to a joint.
A universal joint is a method of coupling that allows for nearly limitless movement of each side of the joint. First developed for factory use, the U joint found its way onto a windsurf mast foot sometime in the 1980’s. Its presence allows a wind surfer to not worry about forcing the sail into position, the way they had to initially. The sail is literally rooted to the board, and all the surfer has to do is angle it to make the best use of the wind.