The 24-inch black ball day shape is the signal ships and boats hoist in daylight to show they're at anchor, aground, not under command or restricted in their ability to maneuver. At 24 in. (610 mm) across, it meets the full-size rule for vessels of any length.

At a glance

Size rule

Annex I of the Navigation Rules (33 CFR 84.06, and the same paragraph in the international COLREGs) says a ball must be at least 0.6 m in diameter and black, and shapes must be at least 1.5 m apart when hoisted together. Vessels under 20 m may use smaller shapes.

When a ball is shown

• At anchor: one ball forward (Rule 30)
• Aground: three balls in a vertical line (Rule 30)
• Not under command: two balls in a vertical line (Rule 27)
• Restricted in ability to maneuver: ball, diamond, ball (Rule 27)
• Dredging or underwater work: two balls on the side of the obstruction (Rule 27)
• Mine clearance: three balls (Rule 27)

Built for working decks

• Black, as the Navigation Rules require
• Two materials: heavy-duty vinyl-coated nylon, or a lighter nylon rope mesh that lets wind through
• Stainless steel or galvanized frame
• Folds flat for stowage and opens rigid when hoisted