A bridle block is for a deflector, and has a stem and a rocker arm attached to each other on a pivot axis. The stem has an attachment for a vessel towline, a forward portion of the rocker arm has an attachment for fore bridle lines of the deflector, and an aft portion of the rocker arm has an attachment for aft bridle lines of the deflector. A hydraulic cylinder has a valve, and is attached to the stem and the rocker arm to hold the stem and the rocker arm in a relative position. The valve is operated by a signal from a control unit. The valve takes an open position when a signal is missing, so there is an open fluid connection between a piston side of a piston and a reservoir or an open fluid connection between the piston-rod side of the piston and the reservoir.