Tuesday, November 8, 2011

The Best Tidal Current Charts

The more I kayak in the San Francisco Bay, the more I realize that a good current chart is slightly more useful than a good tide chart. Sure, if you read a tide chart wrong, you end up stuck in the mud. If you don't know the tidal current, you might be paddling for your life.

Some narrow straits are notorious for fast current, as high as 3 to 6 knots. If you happen to go against the afternoon wind as well, you could really be hurting. That's what happened to me on a paddle trip to the Oakland Estuary. The planner read the current chart wrong and we ended up fighting both the current and the wind. It took us about 15 minutes just to go from one side of the High Street Bridge to the other side! Just as a comparison, going the other way took 5 seconds.

Most people don't realize this, but the maximum tidal current does not happen at high tide, or low tide, or even half way between the two. It all depends on the geography:

  • A large body of water takes a while to fill or drain. In the meantime, water current happens due to the filling or draining.
  • Narrow channels make water flow faster, which means the current is faster.

So it depends on how big the body of water is and how narrow the channel is connecting that body of water to the ocean.

Instead of trying to guess the current from reading a tide chart, which is what many people do without knowing it, the best way is to just read a tidal current chart. Not all locations have a current reading, and seemingly nearby locations have large differences in reading. Again, it all depends on the geography.

Best tidal current chart:


Click on a blue current sensor on the map (in blue). Select the target date. Click on the "Graphic Plot" button and select "960 x 480" or whatever size of the chart you prefer, then click the button "Make Predictions Using Options".

If you would like a good explanation on why tidal current lags tide. Check out this link: