I would think that the sailboat might have a wing keel as my Catalina 250 does. My wife took this picture today of another boater in trouble. He is outside pushing his boat off of the bottom to free it. :) I can't leave the slip as my keel will scrape the bottom even in the channel until the tide height is 2 feet above low tide.

We had an S-2 in Ohio with a similar-looking keel. The weight in the bottom makes it more stable.

I did this once with a 300 foot gas/heating oil tanker entering east rockaway inlet, long island in 1987, when we were just a tad late on the falling tide.

it happens even to professionals in the shallow coastal channels.

Maybe so. It was so long ago I don't remember. I mostly remember the look on my father's face, and it was a long wait for the tide to come up.

I docked a Old Harbor Marina, Clinton.
On beach days at low tide we could walk to the edge of the channel in ankle-deep water I believe the dredged channel was 30ft wide and 8 ft deep at low tide, High tide would give you about 4.5 to 5 feet more depth

Yup. I went to junior high and high school in Hudson, Fla. My dad always had to gaged when he could go out due to high and low tides. Often had to stay out and wait to get back home.