acorn
A cone-shaped piece of wood on the point of the spindle above the vane, on the mast-head.
acorn: wooden finial crowning a ship's mast
An acorn is a turned wooden cone or bulb fitted to the very top of a mast, sitting above the vane or weather vane on the spindle. Its primary function is protective: it caps the exposed end of the mast spindle, preventing water from pooling inside the hollow section and causing rot or rust in the internal ironwork. The acorn also serves an aesthetic purpose, finishing the mast head neatly and signaling the vessel's professional finish to observers ashore.
The acorn is always turned from hardwood, typically lignum vitae, teak, or oak, chosen for water resistance and durability. The shape is a gently tapered cone or bulb, typically 4 to 8 inches tall depending on mast height and vessel class. The base is bored to slide over the spindle, which is usually a wrought iron or steel rod extending upward from the mast cap. A small keeper collar or friction fit ensures the acorn does not rotate or work loose with the vessel's motion.
On larger vessels and those maintained to high standards, the acorn is often varnished or oiled regularly as part of mast maintenance. On working boats, it may weather to a grey patina but still sheds water effectively. The acorn's presence on a ship indicates a degree of care in finish; many working vessels omit it or replace it with a simple metal cap. Fishing boats and commercial trawlers frequently lack acorns altogether, using bare spindle or a flat plate.
The term itself derives from the visual resemblance to an acorn nut: a tapered, rounded form balanced at the crown. The word appears in shipwright manuals from the 18th century onward, though the fitting itself is older. It is sometimes called a masthead finial, though acorn remains the standard term in marine vocabulary. The vane mounted beneath it rotates freely on the spindle, and the acorn prevents the vane from rising and jamming against the mast cap.
Replacement acorns are stock items in traditional shipyard work and are still turned to order by woodworkers specializing in mast and spar work. When the wood becomes checked, split, or simply weathered beyond restoration, the acorn is unscrewed or tapped off and a new one fitted. This is straightforward maintenance, requiring only removal of the vane, the acorn itself, cleaning of the spindle, and reinstallation.