Most recognize the outhaul as the principal way to pull the mainsail out of an in-mast furling mechanism. Those who flake their sails probably have a better understanding of how to properly use this sail control device. During my training, we did nothing more than pull the sail all the way out when we were ready to get going. Once I acquired Skiron, I sent some photographs to the former owners of the vessel and they pointed out a few things to me regarding how I had too much camber in the sail. This is another way of saying that the draft was too deep for the point-of-sail. That’s when I started learning about the outhaul and other mainsail controls.
As I have learned, the outhaul is not simply the line that one tensions to pull the sail out of the mast. Of course, it serves that purpose. And, on in mast furling systems, pulling the sail in part of the way with the furling line allows us to reef the main to depower (and decrease weather helm, too).
Importantly, the outhaul controls the depth of the draft in the lower third of the mainsail.
The outhaul should be tensioned to flatten the sail to depower in heavy winds or when needing to point high. This change may be made just prior to a decision to reef the sail.
The outhaul should be detensioned to increase the draft in light winds and probably also in heavy seas.
As is the case with most mainsail controls, the outhaul is rarely changed without a change in some other control. For example, the adjustable backstay and halyard also require simultaneous adjustments, not because the outhaul is adjusted but because of the wind conditions and desired effects necessary to optimize sail performance.