The basics: what is current and why is it important:
A current is simply water in motion. For freshwater, this is caused by gravity. Water flows downhill. For the ocean, tidal currents are caused by tides, wind, changes in temperature and salinity or some combination. Paddling with the current is faster and requires less energy. Paddling against the current is slower and requires more energy.
Tidal currents occur in oceans, near the shore, and in bays and estuaries along the coast. The movement of water in this case is caused by the gravitational pull of the sun and moon. Unlike rivers and streams, these currents change in a regular, predictable pattern.
In the case where there are sustained winds, the power of the air moving over water also creates current as it drives the water near the surface in a specific direction.
What is an eddy?
An eddy is a circular current of water.
If you’ve ever seen a small whirlpool of water when you paddle on a river, stream, bay, estuary, or ocean, this is an eddy. Eddys form wherever there are areas where current is impeded. They can form behind an obstruction like a boulder or structure like a dock or channel marker. They can also form on bends in the river or waterway and along the shores away from the main channel.
This image is originally from a fly fishing site, www.flyfishusa.com, but it gives a good description of where an eddy forms. Imagine you are a trout instead of a SUP.
Why are eddys and currents important? Because when you are in a race, you can use your knowledge to find the fastest water. If you have a basic knowledge of where the currents are in any particular setting, you can find the fast water or simply avoid the slow water.
This is a view of the current under the Wrightsville Beach Drawbridge
Notice the water is flowing from the top of the photo to the bottom. The current is being disrupted by the pilings. If you are heading away from the bridge, the swirls are the place to be. They are out of the current or channel and actually hold water that is flowing against the tide, or in your desired direction.
If you are heading with the current, stay right in the middle. Although you have to be really conscious of boat traffic, because they have the right of way, they are bigger, and they stay in the channels.
When the current is moving with you, an eddy will be moving in the opposite direction. When the current is moving against you, the eddys move with you.
There is an art to reading water. It isn’t something that you learn overnight, but once you start looking for eddys and currents, and experiment to see where the fast water is, you will begin to reinforce this skill. Eventually, it will become second nature. And in a race where all things are equal, the person in the fast water will get there first. People who paddle in rivers and streams get this. They grew up ferrying across the current and using the eddies to travel upstream.