When going through narrow bits of water, it's especially important to understand which direction the water is traveling, how fast, and how much. There are areas that must be traveled through at "high slack" which means that the water is as deep as it gets and it's not moving at all. What is calm and lake-like at high slack can be filled with exposed rocks, dangerous rapids and overfalls at other times.
Before going through Sergius Narrows, we waited for high slack at Sinbad Point. It was a quiet place, and rather than taking a nap, I took a painting break.