A daggerboard is a removable, vertical foil, typically made of fiberglass, wood, or aluminum, that slides up and down through a trunk in a small sailboat's hull to provide lateral resistance. It reduces sideways drift (leeway) when sailing upwind, and can be fully retracted in shallow water or when sailing downwind to minimize drag.

Key Characteristics and Components
Function: Acts as a vertical keel, generating lift and preventing lateral slippage, allowing for sailing to windward.

Operation: Manually raised and lowered, often operated by a rope or strap handle attached to the top.

Trunk/Case: The housing unit in the hull where the board is inserted and stored, Glen-L mentions.

Positioning: Unlike a pivoting centerboard, a daggerboard moves vertically in a single perpendicular position.

Materials: Frequently constructed from Fiberglass Reinforced Plastic (FRP), epoxy, or aluminum.

Performance: Offers higher efficiency than fixed keels, allowing better upwind performance.

Advantages and Disadvantages
Advantages: It can be fully removed when sailing in very shallow water, beached without damage, and adjusted to reduce drag off the wind.

Disadvantages: It takes up space in the cockpit, cannot pivot when hitting ground (leading to potential damage), and requires a trunk.