We made one years ago out of a 2 circles cut out of plywood, drilles a series of holes around the outside and inserted wooden dowell rods to form a spool, a piece of conduit with a pulley on the end. A "C" clamp or 2 to mount it to the boat. Cant really remember how we mounted it all together but it worked OK. A clothes pin or one of those "Chip Clips" used for sealing up a potato chip bag would work for a release. A old sock with a few rocks for a downrigger ball. Good Luck.
