RS Quba Rigging Manual page 16

If you have the sleeved sail and wish to reef it, attach the downhaul line to the eye on
the front of the sail and take it through the cleat below.
If you do not wish to reef the sail but require a more powerful downhaul, tie a figure
of eight in one end of the downhaul and take it up through the hole in the starboard
side of the boom jaws, through the block with a hook and back down through the
hole in the port side of the jaws, and then to the cleat on the port side of the mast.
The hook then goes into the eye on the sail (the tack).