Abstract: A planing amphibious vehicle has at least one trim tab at its stern. A vehicle control system includes a mode change controller and a trim tab controller. The mode change controller informs the trim tab controller when a mode change event is taking place. The trim tab controller retracts the trim tabs if the mode change is from marine to land mode; and deploys the tabs if the change is from land mode to marine mode, to assist the vehicle in rising on to the plane. The controller may also retract the tabs if the vehicle reverses; and deploy the tabs if a change is made from reverse to forward motion. The vehicle control system may connect to actuators and sensors for retractable road wheels, which may use hydropneumatic struts. Safeguards against system faults and/or erroneous switch operation are included. Road wheel drive decouples are used; a marine drive decoupler may also be fitted.

Abstract: Amphibious vehicle has at least one system which is actuated or has its mode of operation changed when the vehicle changes from land mode to water mode or vice versa. The vehicle comprises sensor means which produce an output signal which varies in relation to the proportion of the mass of the vehicle which is buoyantly supported by a body of water. The sensors may sense the position of a wheel relative to the body of the vehicle. This may be achieved by checking the position of a suspension member. The sensor means may comprise a linear sensor or a rotary sensor. The sensor may comprise a potentiometer. Control means may average the output of the sensor over time. Where several sensors are used, control means may process output signals from each sensor to provide an overall output signal. A water presence sensor, such as a thermistor, may be used to provide a second control signal.

Abstract: Amphibious vehicle (1, FIG. 1) has retractable road wheels (2, 2?, FIG. 1). This may allow planing. During marine travel, at least one wheel may droop below the water line. This increases drag, particularly when cornering. Suspension height sensor 22 may be arranged to detect a threshold beyond which the wheel should not be allowed to droop over water, unless mode change is in progress. When this threshold is passed, pump 18 co-operates with controller 15 to pump fluid into lower chamber 7? of actuator 5 to retract the wheel. Switchable valves 9, 19, 21, and 23 are provided to allow adjustment of fluid chamber volumes. Gas filled accumulators 11 may be provided where a hydraulic suspension is used. Numeral 42 represents an adjustable trim tab. FIG. 4 shows an alternative fluid system layout, with valves 19, 19?, and 110 to allow fluid to be returned to tank 18?.