Downhaul

A downhaul is a line or system of lines used on a sailboat to apply downward tension to a sail, typically at or near the tack (the lower, forward corner) or head (the upper corner). Its primary purpose is to flatten the sail and control its shape, especially in stronger winds. By increasing tension along the luff (the forward edge of the sail), the draft (curvature) is pulled forward and reduced, making the sail more efficient in higher wind conditions.

The specifics of a downhaul system vary depending on the type of sail, boat, and sailing conditions. For example, a downhaul on a mainsail might be a simple line running from the tack down to the base of the mast or a more complex tackle system offering greater mechanical advantage. Similarly, a downhaul on a headsail or spinnaker might run from the head of the sail down to the deck or bow.

Adjusting the downhaul is a key part of sail trim, allowing the sailor to optimize the sail's shape for different wind strengths and points of sail. In light winds, the downhaul might be eased to allow the sail to have a fuller shape, providing more power. In heavy winds, the downhaul is tightened to flatten the sail and reduce heeling (leaning) and weather helm (the tendency of the boat to turn into the wind).

The effectiveness of a downhaul is often linked to other sail controls, such as the outhaul (which controls tension along the foot of the sail) and the halyard (which raises and tensions the sail). A coordinated adjustment of these controls is essential for achieving optimal sail performance.