I joined about three weeks ago.
I had a guest at the helm, and we were passing G 13 on the Sakonnet River (Rhode Island) heading south at about 5kts. We were watching another vessel further west of our position. I was familiar enough with the charts to be concerned about increasing the distance from the plotted rock, but I also knew that we should not have been in trouble. Suddenly BANG!, and we slowed drastically. Then BANG!, BANG! BANG! as we continued to bump the rock... Scared the hell out of me, and scared my guest from the wheel. I took over and got us out, then checked the bilge to find all OK. Later that day I dove on the keel, and it looked like nothing happened.
My current theory is that a swell dropped us on top of a ledge...
Here is a pic from the plotter showing where I turned us around and got us out of there.
Here is the log from the chartplotter:
8/11/2013 4:57:29 PM 15 ft 245 ft 0:00:30 5 kt 205° true N41 37.062 W71 13.295
8/11/2013 4:57:59 PM 16 ft 208 ft 0:00:30 4 kt 198° true N41 37.026 W71 13.318
8/11/2013 4:58:29 PM 16 ft 40 ft 0:00:30 0.8 kt 171° true N41 36.994 W71 13.332
8/11/2013 4:58:59 PM 16 ft 55 ft 0:00:30 1.1 kt 331° true N41 36.987 W71 13.331
My boat draws 5.7' not 20'. The chart of the Sakonnet river is WRONG
However, this stuff happens