Thanks for putting so much effort into your answers. You gave a lot of good info.

We sail a Dragonfly 1200 trimaran (12 meter) and need 3.5 feet of water to anchor, 4 feet to keep the kick-up rudder down, 6.5 feet with centerboard full-down. Centerboard and rudder are designed to kick up if they strike bottom, and the prop is protected by a skeg, so we might get a ding but no structural damage unless we go aground with the hull (been tested)). Coral heads or steep ledges would be the biggest concern.