A hydrofoil assembly for a waterborne vessel, comprising: - a body; - a hydrofoil pivotally attached to the body, optionally the hydrofoil has a symmetrical foil section, - a control mechanism (33, 35, 41, 59) operative to control the adjustment of the hydrofoil relative to the body; the control mechanism comprises: - a sensor comprising a displaceable wand pivotally mounted to the body responsive to the altitude of the vessel relative to the water; - a controller arranged to provide a control output based on responses of the sensor; - an actuator in the form of a pushrod arranged to vary lift in the hydrofoil based on the controlled output of the controller to change the incidence of the hydrofoil relative to the body, wherein - the hydrofoil is configured such that during forward motion of the vessel water flowing across the hydrofoil biases the hydrofoil to pivot to a neutral position in which no lift is generated; and - the control mechanism (33, 35, 41, 59) is operative to displace the actuator to push down in one direction on the hydrofoil to provide a biasing force to the hydrofoil to change the incidence of the hydrofoil relative to the body to create lift, the control mechanism is non-reciprocating so as to be inoperative to apply a biasing force to the hydrofoil in the opposite direction to the one direction, and in the absence of the biasing force by the actuator the hydrofoil is configured to be freely pivoting and is biased in use to return to the neutral position by water flowing across the hydrofoil. - a body; - a hydrofoil pivotally attached to the body, optionally the hydrofoil has a symmetrical foil section, - a control mechanism (33, 35, 41, 59) operative to control the adjustment of the hydrofoil relative to the body; the control mechanism comprises: - a sensor comprising a displaceable wand pivotally mounted to the body responsive to the altitude of the vessel relative to the water; - a controller arranged to provide a control output based on responses of the sensor; - an actuator in the form of a pushrod arranged to vary lift in the hydrofoil based on the controlled output of the controller to change the incidence of the hydrofoil relative to the body, wherein - the hydrofoil is configured such that during forward motion of the vessel water flowing across the hydrofoil biases the hydrofoil to pivot to a neutral position in which no lift is generated; and - the control mechanism (33, 35, 41, 59) is operative to displace the actuator to push down in one direction on the hydrofoil to provide a biasing force to the hydrofoil to change the incidence of the hydrofoil relative to the body to create lift, the control mechanism is non-reciprocating so as to be inoperative to apply a biasing force to the hydrofoil in the opposite direction to the one direction, and in the absence of the biasing force by the actuator the hydrofoil is configured to be freely pivoting and is biased in use to return to the neutral position by water flowing across the hydrofoil. - a sensor comprising a displaceable wand pivotally mounted to the body responsive to the altitude of the vessel relative to the water; - a controller arranged to provide a control output based on responses of the sensor; - an actuator in the form of a pushrod arranged to vary lift in the hydrofoil based on the controlled output of the controller to change the incidence of the hydrofoil relative to the body, wherein - the hydrofoil is configured such that during forward motion of the vessel water flowing across the hydrofoil biases the hydrofoil to pivot to a neutral position in which no lift is generated; and - the control mechanism (33, 35, 41, 59) is operative to displace the actuator to push down in one direction on the hydrofoil to provide a biasing force to the hydrofoil to change the incidence of the hydrofoil relative to the body to create lift, the control mechanism is non-reciprocating so as to be inoperative to apply a biasing force to the hydrofoil in the opposite direction to the one direction, and in the absence of the biasing force by the actuator the hydrofoil is configured to be freely pivoting and is biased in use to return to the neutral position by water flowing across the hydrofoil.