I hit either the buoy weight or a rock while in the channel two years ago on Lake Champlain. The lake was very low and I should have been moving slower and given the buoy more room but hindsight is 20/20. I was doing 6 knots. The boat did not stop but felt as if I had just gone over a sand bar maybe or a submerged log. I felt it go up and back down, stopped, checked the bilge, saw no water, and continued on. It was not until I hauled out for the winter a few weeks later that I noticed a good sized gouge on the front of the keel. I gotta say that laying on your back and feathering out 1.5" of glass around 16" is no fun. Not a tremendously complicated job but had to wait until spring when the hull was bone dry. Working overhead with West Epoxy is also a challenge and invariably a sticky mess. Luckily I discovered another really lousy, quick repair done in the same spot that got fixed in the process. My Alberg is an internal ballast type deep keel which, I guess, is pretty tough.