The depth of the draft on a gaff-rigged catboat is only controlled by the outhauls, and there are two of them. Since the gaff  is in a remote location while sailing, set your gaff outhaul tension before you raise the sail to match the expected winds. If  needed between races, drop your sail and re-adjust the gaff outhaul. The boom outhaul adjustment is very effective to  change the depth of draft in the lower half of the sail while sailing. In light air upwind, the boom outhaul should be tight  enough to just remove the deep wrinkles coming up from the boom. As the wind increases and the boat starts to heel,  tighten the foot with the outhaul proportionately. With 12 knots of wind the outhaul should be as tight as you can get it.  The position of the draft is easy to control in a four-sided sail. The twin halyards of the gaff-rig allow you to easily tweak  the draft position and entry shape. This is the major unique tool of the gaff-rig; there is nothing like it on a three-sided  sail. Watch your sail as you adjust the peak halyard and observe the resulting change of draft position. The four photos of  a sail viewed from the cockpit demonstrate this progression of draft position as the peak halyard is raised. With increased  peak halyard tension the draft will move forward, affecting the entry shape that we call “deep throat.” This amazing  control of the draft and entry shape by the peak halyard is a major key to maximizing your sail’s performance. Twist is the tendency of the sail to rotate away from the perpendicular of the boom as it rises from the deck. This is a more  complicated problem to control in a four-sided sail since the gaff is free-floating around the mast at its saddle, and there is  no vang. Twist is necessary for proper sail shape because the apparent wind direction actually changes at different levels  of the sail. The difference in the direction of apparent wind from the deck to the peak is greatest in lighter winds, and is  minimal in strong winds. Therefore, twist should be greater in light air and less in a breeze. In a marconi (three-sided) sail with a vang, the amount of twist can be confidently matched to the wind above the deck. In  a gaff-rig catboat (four-sided) sail the only controls effecting twist are the mainsheet and the peak halyard. When sailing  close hauled or on a close reach, the mainsheet actually pulls down on the boom more than it pulls the boom toward the  center of the boat. This is the only time that you have good control of the twist by mainsheet tension. The peak halyard  also tightens the leech, and as a result controls twist. However, the proper tension on the peak halyard to position the  draft in the sail is so important to performance that its function to control twist is usually ignored.  Depending on the strength of the wind, you’ll want to adjust the sail shape to most efficiently take advantage of the  conditions. In light air, first raise the throat halyard to tension the luff loosely, so that the sailcloth seems to sag slightly  between the mast hoops. Then raise the peak halyard to remove the long wrinkle from the throat down to the clew. The  body of the sail is now smooth and the draft should be around 35 to 40 percent aft of the luff. This is referred to as “flat  throat.” The wind does not have to bend very much to stay next to the sail. The mainsheet is eased, keeping the boom well  off the transom corner, allowing a smooth exit of air off the trailing edge of the leech. This is your drifting, light air shape,  sometimes requiring a slight leeward heel to let gravity assist to shape the sail.  Now let’s look at what we need to do to when sailing on different points. When reaching, ease the peak halyard and the  throat halyard as you bear off to maintain the same relative position of the luff curve to leeward of the mast, and a  powerful deep throat shape. On a close reach, deep throat draft forward is max power. It doesn’t get any better than this.  20 Points of sail  Trimming to conditions  Twist  In practice, to measure the position of the draft, use your reef points to estimate the length of the sail in percentage points.  For example, if your sail has five reef points, they divide the sail into roughly six equal distances of about 17 percent each. In moderate breeze a deep throat can be very fast. First, tighten your throat halyard to create a smooth entry in the luff.  Then tighten the peak halyard to move the draft into deep throat. You will find that there is extra sailcloth forward along  the luff that allows the luff to slide to leeward of the mast creating a smooth flow of air along the backside of the sail as it  passes the mast. The sheet does not have to be eased as much to keep the leech open in moderate breeze. The best  indicator of the match of twist with the apparent wind is your leech telltales. Upwind the high leech telltale should stream  aft more than half of the time, and the lower leech tell tale will only appear 20 percent of the time. As the wind strength increases the rig becomes overpowered, and deep throat and the extra power it creates is no longer  needed. Therefore, in heavy air depower by easing the peak halyard, which will move the draft aft to 35 to 40 percent.  Keep the throat halyard tight enough to allow a smooth entry along the luff. Ease the mainsheet to increase twist, spilling  power from the top of the sail to decrease heel and helm. Sailing deep and keeping the boat flat seems to be fastest upwind  in heavier air, particularly since there usually is a chop to sail against in these conditions. If you are sailing light or solo in  a breeze (12 or more knots) and do not wish to reef, then sailing with a bubble in the luff and pinching in the puffs is your  only option.