I know a few experienced boaters, even a licensed pro who can't get it through his head high and low don't necessarily coincide with slack. He even recommends only crossing bars at high slack, whatever he means by that because he doesn't understand the difference between high and slack.
I made a different kind of rookie mistake. Not reading the current graph correctly in OpenCPN.
Since Nobeltec bought and shutdown Tides and Currents software years ago I don't have any good recommendations for stand alone tide and current predictions.
To correct myself today I used
NOAAs current predictions off the web.