Operation of T-Foils and Stern Tabs to Improve Passenger Comfort on High-Speed Ferries

Abstract

_ High-speed ferries of around 100mlength cruising at around 40 knots can cause significant passenger discomfort in head waves. This is due to the frequencies of encountering waves, of maximum hull response to encountered waves and of maximum passenger discomfort all falling within a similar range. In this paper, the benefit obtained by fitting active T-foils and stern tabs to control heave and pitch in head waves is considered. Ship motion responses are computed by numerical integration in the time domain including unsteady control actions using a time domain, high-speed strip theory. This obviates the need to identify transfer functions, the computed time responses including nonlinear hull immersion terms. The largest passenger vertical accelerations occur at forward locations and are best controlled by a forward located T-foil acting in combination with active stern tabs. Various feedback control algorithms have been considered and it is found that pitch damping control gives the greatest improvement in passenger comfort at forward positions. Operation in adaptive and nonlinear modes so that the control deflections are maximized under all conditions give the greatest benefit and can reduce passenger motion sickness incidence (MSI) by up to 25% in a 3-mhead sea on the basis of International Organization for Standardization (ISO) recommendations for calculation of MSI for a 90-minute seaway passage. Introduction When the first high-speed, lightweight catamaran car ferries were developed, it quickly became apparent that motion control systems were desirable to improve passenger comfort. This was a direct consequence of the high operating Froude numbers (based on waterline length) of up to 0.75, which gave rise to heave and pitch motions in excess of the wave height and wave slope. It was also a consequence of the period of encountered waves at high speed that becomes close to the period at which passengers would experience significant motion discomfort, approximately 5-6 seconds. As a consequence, active motion controls were introduced and have been fitted to most vessels operating on routes where significant wave heights might reach or exceed approximately 3m.