Slack water at Sandy Hook, New Jersey occurs 50 minutes after high water and one hour and 10 minutes after low water and lasts about 25 minutes.
"I would have thought that slack water would occur at the time of high or low tide, but that is apparently not the case. How exactly does slack water occur"?
We are looking at two physical processes here. The water is moving vertically, up or down, due to the combined effect of the gravitational pull of the moon and the sun on the water on the surface of the earth. This is the tide phase and the times correspond to the what you see on the tide chart.
At the same time (simultaneously) the water is moving horizontally, out or in at a specific location. This horizontal movement of water has inertia or momentum and takes additional time for the water to come to rest and reverse direction once in motion. (Newton's Law, an object in motion wants to stay in motion etc etc etc,.) This is called tidal current and times of slack current can be found on a tidal current chart. So the water will not stop moving in or out necessarily at the time of dead high or dead low on a tide chart.
In fact in some inlets, like Barnegat Inlet the tide can be getting higher while the water is still moving out.
Keep what is happening vertically (tide) to the water separate from what is happening horizontally (current) and you got it figured out.
So how does this relate to our fishing? Many times a particular hot bite for albies, bass, or blues might occur at a particular stage of the tide, let’s say for example slack. If you go by your tide chart the time that is noted for slack may not actually be the time that it occurs. For this time you would need to also reference a tidal current chart for the particular location that you are fishing. This chart will take into account the time delay and will allow you to put yourself in the right place at the right time.
Either side of slack high is usally the most productive simply time to fish because more water is on the beach. For striped bass the top of outgoing is preferred, Capt Jim