Monitoring and control system

A method of controlling the angular orientation of at least one variable fluidfoil 52. The method comprises the steps of: a) receiving detected fluidfoil angular orientation data for the at least one fluidfoil 52; b) receiving a fluidfoil angular orientation demand; c) generating a modified angular orientation demand by modifying the fluidfoil angular orientation demand before it is used to control adjustment of the at least one fluidfoil 54, the modification being performed using the detected fluidfoil angular orientation data; and d) outputting the modified demand and controlling the at least one fluidfoil 54 angular orientation in accordance with the modified demand.