The Sonar Foil System is connected to the board by a lightweight CNC-machined aluminium Board Adaptor with a tapered geometry locking connection that engages with the mast, fusing Board Adaptor and mast together to build one union for optimum load transfer and a stronger, more direct feeling and steering impulse when foiling. FE-Analysis allows us to increase strength in the areas of highest stress concentration and reduce unecessary weight in lower stress areas. Incorporates a strong geometry locking connection for better energy transfer and a more direct feel.