Are you looking for the distance from the deck at the backstay chainplate? A couple of thoughts: The distance will vary depending on the displacement of the individual boat (tools, beer, BBQ's, ets), and how it's lying on its lines (bow or stern heavy). Over the long weekend, I'll try to drop a line and then measure it. In the distant past, the racing fleet floated a straight edge under the bow and stern and dropped a plumb line to measure the distance. We were trying to determine displacement without actually weighing the boats. Maybe I can find those data . . .