Its one of the early roller reefing systems for a mainsail. Not very good and considered obsolete now. The other stuff you see was added later, after the boat was made.
All the best,
Study the history of naval architecture and move forward knowing what didnít work before.
Donít waste time making the same old mistakes but instead make new ones and to insure your place in history be sure the mistakes are big ones.
Never design a mast that is weaker then the boat
Never design a boat that is weaker then the mast
Never listen to someone describe why your project will not work unless they can show you the broken pieces of their own version.