Composite timber joints freed sailing ships from tree size

What was the most significant innovation in Age of Sail ship design?

The development of strong built-up timber members and joints, which allowed ship size to exceed the limits imposed by individual trees.

Built-up wooden structures and improved joining methods as a foundational change in sailing-ship construction. Earlier shipwrights were constrained by the dimensions and shapes of individual trees when producing long beams and other major members. Reliable joints allowed several pieces to behave as one structure while enduring the repeated working loads of a hull at sea. Once that constraint eased, larger ships and later first rates became practical, and many other design advances could build on the new structural freedom.