Let's take our compass away for a moment and steer the boat toward a GPS waypoint by matching course over the ground (COG) to the bearing to the waypoint. (See "Steering by COG without a Compass," page 66.) We're doing well, and the track on the plotter shows our course as a straight line with the waypoint dead ahead. As we approach our waypoint, which happens to be a navigation aid, we begin looking for it to confirm how totally reliable our instruments are. Where should we look? Dead ahead, like the plotter says? Maybe not. We're on port tack, on a close reach, and making 10 degrees leeway, and a current is also setting us left to right (which we weren't aware of). The mark isn't dead ahead; it's 30 degrees to starboard, behind the genoa. Clang!