In the field of aeroelasticity, flutter is a well-known instability phenomenon. Flutter is a synchronized vibration which takes place in a flexible structure moving through a fluid medium. It occurs when two regular, rhythmic motions coincide in such a way that one feeds the other, drawing additional energy from surrounding flow. A classic case of wing flutter might combine wing bending with either wing twisting. Flutter appeared for the first time on racing yacht keels with composite fins, so in water, in 2004, on both the IMOCA 60 POUJOULAT-ARMORLUX, which lost her keel, and SILL. Following these problems - particularly following the loss of the keel of Bernard STAMM sailboat, accident that could have dramatic consequences for the skipper - HDS company focused on the phenomenon. This paper will introduce the strategy of HDS faced to the problem and the analytical and numerical methods implemented to estimate the flutter critical speed. Our model is based on a truncated modal basis for the most energetic modes which are generally, for a bulb keel, the lateral bending predominant mode and the torsion predominant mode. One of our requirements was to make a simple model in order to integrate the calculation of the flutter critical speed in the first design loops of a composite or steel keel. Besides, an other requirement was to be able to calculate flutter critical speed on other type of appendages: hydrofoils, dagerfoils, daggerboards, rudders...This model has worked well for the two cases of flutter appeared on IMOCA sailboat keels. Besides, to verify the quality of the model and to complete our analysis of flutter phenomenon on racing yacht keels, a 3 dimensional multiphysic simulation has been developed using the software ADINA.