Abstract: Automatic trim tab control system (10) for boats in which the controls are provided with an attitude sensing switch (14) which provides port/starboard, fore/aft correction signals to the system (10) for trim tab correction. A timing means (18) in the control system enables signals from the attitude sensing switch, if corrections are required, to be amplified (16) and then directed to the switching relays (20) for the trim tabs or other device requiring altitude correction. A digital embodiment (134) may also be used for applications other than boats.