Had a great solo sail on Lark for the first time in a week, and enjoyed 10 knots true windspeed from the South. On the way back, stopped by friends on their dock to chat, and then shoved off towards home at around 4 pm. But didn't watch where I was going, nor my own depth gauge. Felt me hit and looked at gauge, and it said 3.5, and Lark draws 4.5 feet. Tried to sail off. Nope. Tried to use engine to get out. Nothing. Called a friend, who came out in his 18 foot 115 horse Bayliner. Seemed to come close several times, but couldn't pull it off. Low tide was approaching, so they helped me set my anchor with 100' of rode out. Figured to come back at midnight and retrieve her at high tide. Another neighbor then came by with 24' center cockpit with a 300 horse yamaha on the back, and asked where to put the boat once he got it off. I then joined him and his son on his boat, and once we retrieved the anchor, used the rode to pull Lark off the sand bar. Took two tries, and the strain was evident, and she then slid forward, free. He towed Lark home with his son and I onboard; I showed his son how to steer a sailboat all the way into the slip. No harm done to the keel, though some paint has been scraped away by the mud/sand on the bottom. SO relieved to have Lark back in her slip!