A deflector device (22) for use with a tow lie between a towing vessel (10) and a tow (16) in water behind the vessel, the device comprising a principal wing-shaped body (28) shaped to produce in use a sideways force which urges the tow line (16) laterally with respect to the direction of movement of the towing vessel, a boom (32) extending rearwardly from the principal wing-shaped body (28), and an auxiliary wing-shaped body (52), smaller than the principal wing-shaped body (28), secured to the end of the boom (32) remote from the principal wing-shaped body (28) and shaped so as to produce in use a sideways force in generally the opposite direction to that produced by the principal wing-shaped body (28).