A rotor sail is a cylindrical auxiliary propulsion device that generates thrust via the Magnus effect when the cylinder is spun in crosswinds, improving fuel efficiency. Because wind speed generally increases with altitude above sea level, rotor sails are typically designed to be tall (often >20 m) so that the aerodynamic gains outweigh the power required for rotation. In practice, however, rotor-sail height is constrained by bridge clearance and port regulations. Commercial systems address this by adopting very tall rotor sails (≈35 m) combined with a tilting mechanism to reduce the effective height when needed.

This project explores an alternative to full-body tilting by folding only the upper portion of the rotor sail. We investigate an origami-inspired deployable concept based on Sarrus linkages to enable Z-axis (height) contraction/extension to meet operational height constraints. The study focuses on (1) achieving a near-perfect cylindrical geometry in the deployed state and (2) withstanding self-weight and centrifugal loads during operation (e.g., a ~5 m-diameter cylinder rotating up to ~180 rpm) while maintaining low mass to avoid compromising vessel stability.

We adopted a staged prototyping approach to validate target patterns and locking mechanisms, progressively increasing scale to address scale-dependent issues and refine the structure. A key challenge was developing a locking strategy that can withstand high centrifugal acceleration (≈90G) under strict mass constraints.

To achieve this, we implemented a two-level locking concept :

1. Primary locking : We used a double-layered Sarrus linkage (instead of a single layer) and introduced an internal plate to preserve cross-sectional geometry, with a first-stage locking mechanism connecting the plate to the surrounding facets.

2. Secondary locking : We added specialized locking devices along the side faces of the Sarrus links to create a hoop-stress load path, improving resistance to centrifugal loads during rotation.