Tides are the rise and fall of water levels as dictated by the moon. High tide occurs every 12 hours and low tide also every 12 hours. The tide rises for 6 hours, then falls for 6 hours, over and over, every day for all time.
The incoming tide is called a "Flood Tide" and the outgoing tide is called an "Ebb Tide". It makes since when you think about it because a floor tide will flood low level tidal land and when the tide recedes, it "ebbs" away.
Tides are simple to comprehend as they are easily visible, but currents are what can be really fascinating! It may seem obvious that as the tide comes in, the current will also flow in and as the tide ebbs, the current also flows out.
What might not seem too obvious at first is that at slack tide, when the high tide is at its highest and then begins to fall, the current can still be flowing! As the tide ebbs, the current can still be flooding! It is even possible for the current to never change direction as the tide floods and ebbs. This begs the question: How can water flow in while it is flowing out?
Currents and tides may seem interlocked, but they are actually two separate animals. Tides are merely the height of the water level, and current is the flow of water. If you have a large river that drains into the ocean through a narrow inlet, the current may always flow out even with a strong tidal variance. Having more water present will cause the tide to climb, but the current can still flow regardless of water levels.
When you are looking at waterways, it will be a huge help to learn the local water patterns. Look up tides and the currents in areas to see if you can figure out how they operate. If you can't get the information, it would be helpful to just anchor and observe it for a while.
While transiting the ICW, we have encountered some very strong currents and we use them to help us travel south, towards our destination. The tides will rise and fall, but the currents seem to run on their own schedule, several hours delayed of the tide's shedule. By anchoring, we can visually see the intensity and direction of the tide by looking at the anchor rode.
When the current is strong, it will actually form a wake behind the rode. When the current reverses, the boat will actually shift direction, letting us know the change has occurred. Writing down the times it changes is helpful as this lets you know when you will be traveling and makes sure you are prepared to leave when the tide will become in your favor.
Once moving, looking at other stationary objects will help you determine the intensity and direction. The wake will always form on the downstream side of the object and the larger the wake, the stronger the current. Buoys will also tip over and create a wake when the current is strong!
When the current is helping you, enjoy the bonus speed that it gives you. When the current is on your nose, drop anchor and wait for conditions to improve. Pushing along against the current is foolish when in a few hours, you will get a hefty push.
If you are unfamiliar with how the local waters operate, simply ask a local fisherman and they will give you all the clues and know-how available to navigate the waters safely and easily.
On a side note, flood and ebb tides are when water comes in or out. Slack tide is when the tide is at its peak or trough and the water level is not changing. With currents, you have the same setup, but the time with no current is called "Slack Water" and this is the time to navigate narrow or dangerous areas, as there will be no current pushing you into obstacles. Slack water only lasts around 15 minutes and occurs only 4 times a day, so if there is an area that requires slack water to pass through it, it will be imperative that you time it perfectly and don't be late!