Abstract: A visual aid for boat skippers to which a skipper inputs information about the relative position of another observed boat and a navigation light color which he observes. The device has a group of input switches each indicating a possible relative position of the second boat. Another group of switches indicates the possible navigation light colors of red, green and white. A display signals whether the input combination of position and lights is a potential collision condition. A collision detecting logic circuit connects the switches to a display for actuating the display in response to actuation of selected combinations of the switches.