Downhaul

A downhaul is a line or tackle to apply downward tension on a sail or spar to control its shape and optimise performance.

The downhaul is an essential control line on many sailboats, particularly for adjusting the tension on the luff of a sail. By pulling the sail down toward the boom or deck, the downhaul helps flatten the sail, which is particularly useful in stronger winds. Flattening the sail reduces its curvature, or draft, which reduces the power generated by the sail, making the boat easier to control and preventing excessive heeling or overpowering.

On a typical rig, the downhaul is attached to the sail’s tack or a fitting on the mast. It is then led down to a cleat or block system, where it can be tensioned. Sometimes, the downhaul is part of a more complex system, such as a Cunningham, which allows for finer luff tension adjustments. The Cunningham is often used on racing sailboats to make precise adjustments to the sail shape while underway.

The downhaul is particularly important in mainsails and jibs, though it can also be used on other sails, such as spinnakers or genoas, depending on the rigging setup. On a mainsail, the downhaul works in conjunction with other sailas the outhaul and the boom vang, controls, such to optimise the sail shape for different wind conditions.

In light winds, the downhaul is typically eased, allowing the sail to take on a fuller shape. This increases the sail’s power and helps the boat move in lighter air. As the wind increases, the downhaul is tightened to flatten the sail, reducing drag and preventing the boat from becoming overpowered. This balance between power and control is a key aspect of sail trim and critical for performance sailing and cruising.

In summary, the downhaul is a vital tool for managing sail shape and performance, allowing sailors to adjust the tension on the sail’s luff to suit the prevailing wind conditions. The downhaul can significantly enhance a boat’s speed, handling, and safety.