The Intact Stability of Wind-Assisted Merchant Vessels

Abstract Wind-Assisted Propulsion Systems (WAPS) are increasingly being considered as a viable solution to reduce the fuel consumption and harmful emissions of merchant vessels, and both system size and the number of installations are steadily growing. A critical factor to safely exploit these systems is the vessel’s stability, which classification societies ensure through the use of additional minimum stability criteria for WAPS-equipped vessels. In contrast to those for motor vessels, for which the International Maritime Organization specifies standardised minimum criteria, there is no harmonised approach. This paper presents the results from a master thesis study analysing the intact stability of WAPS-equipped vessels and these existing additional criteria. It encompassed four types of WAPS from two distinct categories, evaluating intact and dynamic stability criteria and underlying calculation methods and assumptions, in which notable gaps and inconsistencies were observed. The operational characteristics of WAPS were covered as well; it was observed that these can have a significant impact on the stability risk, an aspect not always adequately accounted for, and that the differences between mechanical and conventional WAPS are significant. The study has demonstrated that the various operational and physical characteristics of WAPS are not comprehensively addressed by current stability standards. To ensure suitability for their purpose the additional stability criteria for WAPS-equipped vessels require further development and refinement, keeping in mind both harmonisation and clarity. The adoption of system specific criteria should be explored. This will support the advancement of wind propulsion technology on merchant vessels by enabling a safe increase in system size and efficiency, while also facilitating regulatory compliance. Keywords Wind Assisted Propulsion Systems; Intact Stability; Dynamic Stability; Stability Criteria; WAPS Operational Risks; Sailing Cargo Vessels; WAPS Stability Standards