Mates: Last week we discussed draft depth (belly) and angle of attack. Now we'll discuss DRAFT POSITION. Draft position is the location along the chord line where the maximun depth falls. In other words, what you are doing is identifying the deepest part of the draft depth (belly) and drawing a straight imaginary line from top to bottom through that point of the sail. This straight line will intersect the chord line at some point. Remember last week, when we discussing draft depth, I told you to measure the foot of your sail, which we assumed was 10', and mark the half way point (5')on the boom? That mark comes into play as a reference point. Now, assume the imaginary line you drew from top to bottom hit your reference mark. That would mean that your draft position was 50%. Suppose your line intersected at 4'. That would mean your draft position is 40%. Pretty simple - right? Why is it important to know your draft position? The reason is that draft aft produces more power and draft forward produces less power and is more forgiving. Draft aft and draft forward of what? The key number is 50%. Under normal conditions, the draft position should be about 48% to 50%. In heavy air, the draft position should be about 43% to 45%. Why? Because draft position forward produces less power and your trying to control the boat. The controls used to adjust draft position are the mainsheet, boom vang, cunningham, outhaul and mast bend. Increase tension on those controls and the DP moves forward. Decrease tension and it moves aft. The controls on the jib for draft position are the fairlead and halyard. Move the fairlead forward and the DP moves AFT. Move the fairlead aft and the DP moves FORWARD. Increase halyard tension and the DP moves forward and it moves aft if you decrease tension. Next time your out sailing, devote some time to just moving the DP until you can actually see it moving. Any questions about draft position?
