The easterly winds were strong, so we were staying close to shore to reduce the fetch or build-up of waves. And we were having a great day of sailing in 20-25 knot winds on the beam, with reefed jib, main and mizzen, sometimes doing 'hull speed' of 8.3 knots. Looking at the Navionics chartplotter, Sue noticed an 'x' a couple miles off Punta Guiones, entitled 'BREAKERS'. When we were close to this spot, we saw a long stretch of calm sea with white horses (rough water) on either side of the calm area. We were between the shallows of the shoreline, and this long calm stretch. But we thought we could skirt the problem on the shoreline side. As we continued on south, we realized this calm stretch was 1-2 miles long, and that it was getting closer to shore. Oh, and there was no current which surprised us, because we had been experiencing current through the day. So we approached the calm area in 200+ feet of depth. But in 10 seconds, we went from 200+ to 19 feet before making a sharp turn retreating into the rougher water inside. It was obvious we needed to do a '180', head north, get outside this calm area and then turn south again much further offshore. A mega yacht was approaching the area, and I raised them on VHF radio, letting them know about the danger. Much obliged they turned out, and we went south about 3.3 miles off the point in a northerly current of 1.5-2.0 knots against us. There was some underwater structure that had built up over time around the point. This structure had not been charted. But it was controlling the current around the point. We were grateful to have dealt with this navigation hazard, and were relieved to be on our way safely south.