Crosstree

A crosstree is a horizontal spar on a sailing ship's mast that forms a cross-bar across the mast. It sits near the top of the mast or topmast and serves as a mounting and support point for the upper rigging, particularly the shrouds that brace the mast from the sides. On traditional square-rigged vessels, crosstrees are often mounted in pairs on the topmast and provide attachment points for lines and stays that control the upper sails and the stability of the mast. The area between the crosstrees can also function as a platform for rigging work and occasionally for a lookout, with sailors climbing to it via ratlines.

In design terms, crosstrees are usually timber spars connected to the mast and integrated into the masthead structure. They help distribute the load from the upper shrouds and stays, contributing to the mast’s rigidity under sail. The term is most commonly found in historical or traditional seamanship contexts; on modern ships with different rigging or metal masts, crosstrees may be absent or replaced by alternative hardware, but the concept remains part of the vocabulary of classic nautical rigging.

The word is sometimes written as cross-trees and is closely related to other masthead components such as the topmast, stays, and shrouds. It is primarily of historical interest today, though replicas and traditional sailing vessels continue to use the term in describing their rigging. See also cross-trees, topmast, rigging, and ratlines for related topics.