Another couple of search terms came up about the Mirror rig. I make no claim to expertise in this domain. I just know where to look and my boat has a Mirror rig which I set up every time I go sailing like so many others. I recommend looking at this site which concerns building a Mirror dinghy from a kit you can buy.
Where does a mirror downhaul connect?
Just to be clear about terminology, downhaul is what some call the boom vang, the device for tightening the leech of the mainsail when the boat is sailing upwind.
This image shows the mast step of a Mirror dinghy and the central mast step wooden support (not the thin piece of plywood but the block to which it is attached), linking the mast step to the keel of the boat, ensuring maximum strength. The shackle for hooking the bottom part of the downhaul pulley system is attached to this strong wooden support. The top part of the downhaul is a loop of rope which goes round the boom and is stopped from sliding towards the mast by a small triangular block of wood.
If downhaul means the cunningham for tightening the luff of the mainsail, then I attach one end of the rope to the bottom of the mast, through a pulley attached to the sail’s tack and then down again to a cleat on the foredeck within the sailor’s reach. Thus I have equal access to the cunningham, the downhaul and the outhaul to set my sail. The genuine Mirror has a different system, and attaches the cunningham to the boom. I disagree with that system, as it put stress on the boom gooseneck.
Mirror dinghy with mainsail only?
All sailing boats have their centre of effort in relation to their centreboards, and this determines the balance of the boat between lee helm and weather helm. The Mirror is normally designed to sail with a mainsail and a jib. However, it has a second mast step, further forward, and a second pair of anchoring points for the starboard and port shrouds – these two things making it possible to move the mast forward by a precise distance (as designed by the naval architect) in relation to the centreboard. When this is done, it is possible to sail with the mainsail alone in a cat boat rig.
In a force 4 or less, I can handle my boat with its jib, as the mainsail alone leaves the boat with much less power. I only sail without the jib with a reefed mainsail in heavier wind conditions, which brings the centre of effort forward. Sailing the Mirror as a cat boat can be helpful for the beginner, and it is not without accident that the designer of the Mirror, Jack Holt, provided for this possibility in his design.