Friday, September 3, 2010

Once more into the tide

A few more elements of tides that we need to understand are that the tides don't change like a switch going on and off. They gradually change, and that change is constant. In a normal situation you have 4 tides a day, as I mentioned previously. Two highs, and two lows. If you have four tides a day, and the changes are gradual then they must be fairly even in their dispersal throughout the day. They each last approximately 6 hours - give or take. In actuality tides occur about fifty minutes later each day, (Because it takes the moon 24 hours and fifty minutes to complete a cycle around the earth) which is why our tides don't occur at the same time each day. Tidal changes during that six hours start slowly, build to maximum strength, and then start decreasing in intensity. During the middle of the cycle when the most water is moving, you get the biggest change in tide height. This varying cycle generally follows the rule of twelves. During the first and sixth hours of the cycle 1/12th of the water will move. During the second and fifth hours 2/12ths of the water will move. And during the third and fourth hours of the cycle - the middle two hours - 3/12ths of the water will move.

The important aspect of this is that in the middle of the cycle you have the most movement of water, and at the ends of the cycle the least. In fact at the change of that cycle when we end the 6th hour of the high tide and start the 1st hour of the low tide, in that change over, we are in a period called 'slack tide', this is when the least water is moving.

So there are times when a lot of water is moving, and times when very little water is moving. It is important to know when those times are because while the water is moving vertically, it flows to new areas, as water always seeks its own level. When water flows through a narrow area - a constriction - it goes faster. Like putting your thumb over the end of a hose.

So when you create your float plan, look at the possibilities of water being constricted and a tidal current being created. If there is an area of constriction water will be flowing very fast through that constriction at the middle of the tide. Whereas very little water will be flowing there at slack tide. Plan your paddle accordingly.

For instance, if I am paddling out and back to the same point I want to paddle against the tide on the way out, and back with the tide - so when I am tired I am not also fighting the tide. The same goes for the wind. I would rather start my paddle heading into the wind, so I get a push coming back.

Or perhaps I have to transit an area of high tidal current, but its going to take me four hours to get to it. That means I need to leave the safety four hours before the slack tide, so I reach the area of high tidal current when the least amount of water is flowing through it.

An area like this is not very far from where I learned to paddle. It's an area called 'Hell Gate' and it is in New York State. Three bodies of water converge on a very small opening. The Long Island Sound enters the East river along side Manhattan Island. At the north end of Manhattan island The Hudson river joins the East river. The sound, the East river, and the Hudson river are all tidally influenced. Meaning the rivers reverse there flow when the tide is coming in - or flooding - and then the rivers flow takes over when the tide is receding - or ebbing. (In actuality the East river isn't a river, it is an inlet from New York Harbor, a large bay, and finally the Atlantic ocean.

So when the tide is flooding, water comes from the Long Island sound and floods into the east river. At the same time the Water is flooding the east river and Hudson river. This junction can become very turbulent with a fast moving tidal current.

Other things effect tides and tidal currents as well. The shape of the land surrounding the water, and the shape of the land under the water all will effect the tide, and tidal currents.

It's good to understand tides and tidal currents, but the best way to know how tides effect a certain area of coastline is to get knowledge from someone who paddles there all the time. Local knowledge is key. Seek out paddlers who know the area, and can give you information that can only be learned by putting a kayak in the water.


  1. Think about a water atom in the sea. This particle is affected by the power of gravity. In any case, the Moon additionally applies a weaker gravitational draw on this atom.

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