I took lessons on the Potomac with a Flying Scot just south of the Woodrow Wilson Bridge. There were a couple times where we would just stop in the middle of the river and have to raise the center board because it would snag. That being said, there are some sailboats of pretty good size anchored at Gangplank Marina right under the 395 bridge. I assume they did a lot of tacking in the channel or a lot of motoring. I’ve never seen a sailboat over 25 feet actually sailing in the Potomac though.
Here is the NOAA chart for the DC area - Chart 12289
- Looks like once you get up past Haines point you get some depth, but I'd still be afraid of running smack into a log.