Join Date: Feb 2000
Location: Annapolis, Md
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In light air anything that creates drag is the enemy and increasing drive is your friend.
On the drag side, in almost all ways, weight is the biggest single enemy in light air sailing. It means more hull in the water, which means more turbulence, more frontal area and more wetted surface. Boats with L/D's over 170 or so are operating at a real liability in light air. Long keels, skegs, large rudder areas, large amounts of deadrise all add to wetted surface, all add to drag. Boats with large diameter spars and lots of standing rigging, high freeboard, all kinds of gear on deck and in the rig have a lot of aerodynamic drag as well.
I somewhat disagree that waterline beam much of a factor. Cross sectional area really the more important factor. A boat can be narrow at the waterline, but still have an excessively high cross sectional area, and therefore a high drag. CCA boats are a good example of that.
Then there is the drive side. On the drive side, nothing succeeds like a large, efficient sail plan. With thier large drive for their drag, high aspect rigs really shine in the light stuff plus they get their rigs high enough off the water to help get into a slightly higher gradient wind range. Boats with standing sail pland SA/D's under 20-22 really suffer in light air.
Then there are the things that you can do to opimize the light air sailing ability of a particular boat. The biggest single thing that you can do is to get light weight sails (which will hold their shape in light air better than heavier sails which get pulled to flat due to gravity) and set them properly. Next comes keeping the bottom smooth, fair and clean. Sailing the boat, a small heel angle helps to keep sail shape and also since light winds often have a vertical component, a slight heel helps catch the falling breezes. On boats with comparatively hard chines and flat bottoms, heeling can also reduce wetted surface. On IOR, MORC, and Open Class typeform hulls, going bow down lifts the high wetted surface areas of the stern and so reduces wetted surface as well.
Depending on how light the winds are, you initially want to make your sail shapes fuller to generate more drive, and make sure the slot is open. As the winds lighten further, there is not enough force to push the wind around the sail so flatter sails actually work better in the really lightstuff. Again it is very critical to keep the slot open and air flowing. minimizing helm angle and the amount of movement of the helm is also important. Minimizing movement around the boat also helps since rocking and pitching interupts air flow over the sails and waterflow over the keel.