A remote control unit can be used for a boat having a plurality of propulsion units to perform output adjustment and tilttrim angle adjustment of the propulsion units. When the bridge circuit) has a branch with a resistor network and a transistor connected in series, and the control unit is designed andor has a program so that the adjusting signal for adjusting a resistance value of the resistor network is switchable as the component dependent on the bridge voltage. The end of the optical line may have a first non-perpendicular angle and the side of the phase modulator may have a second non-perpendicular angle. The processor also estimates an illuminance value for each of a plurality of angular paths within the structure.