Outhaul - The main outhaul is an adjustment than does more than first meets the eye. Everyone knows that as you tension the outhaul, the main flattens in its lower third. But most people do not realize that a tight outhaul also opens the lower leech. When beating, the effect of a flatter main and a more open leach means less weather helm. Additionally, the boat will want to point higher and go faster in overpowered conditions, all other adjustments remaining the same, with this flat open shape.
There are some general rules you can follow. When beating in light air, ease the outhaul some to power up the sail. If you have a foot shelf in your main, ease the outhaul until the shelf is about half open. As the wind increases, tighten the outhaul so that the shelf is completely closed. For reaching and running, release the outhaul until the shelf is completely open, but not so much that the foot collapses toward the mast. On a windy reach, tighten the outhaul to depower the main.
A simple 2 to 1 purchase for a Windmill outhaul is all that is needed: out to the aft band up hill in heavy air, less in moderate, completely off down wind. I lead this control to a clam cleat on the forward thwart, some owners led it to both decks, but I do not feel this is a control that must be played. I just set it for the point of sail and forget it. Another way to rig the outhaul is with a Highfield (throw-off), lever attached to the boom, this works quite well. See Figure 7 for details. A method of rigging an internal outhaul with the blocks in an Aluminum boom is given in Construction of an Aluminum Boom for a Windmill. [Note add diagram to this doc.]
An outhaul for a wood boom is rigged differently. You need a sheave, home made?, at the end of the boom to allow 3/32 7x19 SS wire to pass over the end of the boom from the top to the under side. A halyard shackle is attached to the wire, which in turn attaches to the main clew grommet. About half way back up the boom attach the wire to 1/8 or 3/16 line. You may terminate the line near the gooseneck, with a clam cleat screwed to the underside of the boom. (Same clam cleat as used in the vang system, a Race Jr.) Or you may attach a single bullet block with a eye strap to the extreme forward end of the boom and lead the line to the keel to another single bullet block and then back to the thwart and terminate at a clam cleat.