Windlass: Crossbow Spanning Device Explained

A windlass is a crank-operated spanning device used to cock a crossbow whose draw weight exceeds what a shooter can manage by hand or belt hook. It uses a system of hooks, rope, wheels, and rotating handles to multiply force mechanically, allowing an arbalist to draw strings of extreme tension safely and consistently.

When a Windlass Is Needed

Crossbow draw weights fall into rough operational tiers. Bows up to approximately 77 lbs can be spanned by hand. Those over approximately 77 lbs typically require a belt hook. Once draw weight exceeds approximately 150 lbs, a windlass crossbow spanning device becomes the recommended tool. At these tensions, hand-spanning is neither safe nor practical.

How a Windlass Works

The device seats onto the rear of the crossbow's tiller — the wooden stock that houses the trigger mechanism and provides shoulder support. Two metal hooks attach symmetrically to the string; asymmetric hook placement risks scratching or warping the tiller during tensioning. The archer rotates the handles, which wind the rope through a pulley or wheel arrangement, drawing the string back until it seats in the nut — the cylindrical locking piece that holds the string under tension until the trigger releases it. Once the string is seated in the nut, the windlass is detached and set aside before shooting.

How a Windlass Works

The device seats onto the rear of the crossbow's tiller — the wooden stock that houses the trigger mechanism and provides shoulder support. Two metal hooks attach symmetrically to the string; asymmetric hook placement risks scratching or warping the tiller during tensioning. The archer rotates the handles, which wind the rope through a pulley or wheel arrangement, drawing the string back until it seats in the nut — the cylindrical locking piece that holds the string under tension until the trigger releases it. Once the string is seated in the nut, the windlass is detached and set aside before shooting.

Key Components

• Hooks — attach to the string; must be evenly spaced (reference spacing: approximately 67.5 mm apart)
• Handles and cranks — the rotating elements that wind the cord
• Socket — fits over the tiller butt; tiller profile must not exceed approximately 57 × 24 mm for a standard windlass fit
• Rope — transmits crank force to the hooks pulling the string

Windlass vs. Cranequin

These two spanning devices are frequently confused. The cranequin used a rack-and-pinion gear mechanism and was typically mounted along the tiller for a slow, controlled draw. The medieval windlass used rope and pulleys cranked from the rear, and was capable of producing the highest tension of all traditional spanning methods — making it the tool of choice for the most powerful crossbows. Neither should be mistaken for a goats foot windlass lever, which is a simpler, lower-draw-weight lever device with a different mechanical principle.

For broader context on large-scale historical projectile devices, see our glossary entry on the ballista, the ancient torsion-powered siege engine.