Dynamic behaviour and operational limits of stabilizer fins

The efficiency of stabiliser fins is evaluated most of the time with a quasi-static, steady approach, the lifting characteristics being obtained from wind or cavitation tunnel tests. Although this approach can be assumed to be correct when the fins are working at low angle of attack in mild sea conditions, strong non-linearity appears when reaching their limits in rougher sea conditions, like stall or cavitation.
The lifting characteristics and behaviour of the fins under a given control algorithm should be addressed in order to determine accurately their operational limits, both in terms of mechanical angle saturation and risk of stalling. Experimental results obtained in the new Seakeeping and Manoeuvring Basin of MARIN for different vessels and different type of fins are presented. Calculations were also performed with a 3D-diffraction theory code and a 2D-strip theory code in order to get more insight in the hydrodynamic mechanism acting on a stabiliser in activity.