Centreboard (centerboard) – movable lateral appendage for small sailing craft

Design and operation

Typical components include the board itself, a trunk or case inside the hull, and a pivot or lifting mechanism. Some centreboards pivot on a pin and swing up into their trunk; others slide vertically and are known as daggerboards. Raising the board reduces draft for beaching or trailering; lowering it increases directional control and sideways grip while sailing.

Uses and examples

Centreboards are widely used on small open boats and many family sailboats. They are especially useful in shallow waters where a fixed deep keel would ground. Recreational and racing dinghies often rely on a centreboard for performance. For general information on small sail craft see dinghies. When fully lowered in deeper water the centreboard improves a vessel's ability to hold a course and point higher into the wind, contributing to directional stability.

Advantages and drawbacks

• Advantages: adjustable draft for shallow-water access, easier launch and retrieval, lighter weight and simpler trailering compared with fixed keels.
• Drawbacks: centreboards generally provide little ballast, so they give less righting moment than a heavy keel; they add mechanical complexity and require a trunk that occupies interior space and needs maintenance.

Variants and related appendages

Closely related devices include daggerboards (vertical sliding boards), bilgeboards (mounted on the sides of wide-hulled boats), and fixed keels (permanently attached, often ballasted). Choice between these depends on vessel type, intended waters, and performance needs. Practical care involves inspecting the trunk for water ingress, preventing corrosion or rot of the board, and ensuring the lifting mechanism is serviceable.