Monday, May 7, 2012

Currently


This big, beautiful "super moon" that rose a couple of nights ago is causing all kinds of flooding problems because it is closer to the earth than usual.  Tides are higher and lower than average which means currents are also stronger and faster.

The stock market is easier to predict than the currents on the ICW (Intracoastal Waterway).  In keeping with one of our most valuable navigation strategies, the ask-around method, we assumed we would get all of the information about ICW currents from the seasoned sailors who gather at the dock for coffee every morning.  Our cruising guides and navigation charts gave directions like "currents change every 3 miles through this area".  Change from what to what?  When? Which direction?  With 9 foot tides and up to 3 knots of currents, we needed more information about when, where, and how much.  Our dock gurus looked at us blankly, shrugged their shoulders, and said, "Good luck with that."  After decades on the ICW, they had no idea.  All we knew, in the words of a former president, was that they would be  "either fer us or agin us" and so far they are usually agin us.

Currents are water movement and tides are the rise and fall of water levels.  They are both caused by the gravitational pull of the moon but are also affected by the earth's rotation, shoreline configuration, ocean floor topography, and in the case of currents, temperature and wind.  The currents we are dealing with in the ICW are primarily caused by the water rushing in and out of creeks and rivers because of the rising and falling tides but we have yet to see much of a pattern in speed and time.  At times it seems we will be sailing with a rising tide yet will have 3 knots of current against us.  That can make quite a difference when we are only going 6 knots.   Then it will suddenly change directions.  Here is a chart we used last week with the ICW route marked by a pink line.  Every time we turned a bend into a new river or creek or one flowed into or away from the one we were in, we knew the current might change.  Hence the stock market effect.



We can tell how fast the current is going using our transducer which tells our speed relative to the water.  If it only reads 3 knots and our GPS says we are moving at 6 knots then we have a 3 knot current helping us out.  In keeping with our second navigational mantra which is to never rely completely on technology, there are ways to read the currents without electronics.  The most obvious is to watch any stationary object in the water such as a channel marker post, mooring ball, or anchored boat.  I can see how the water wraps around it and leaves a line as it rushes past.  In this case, the current is moving from right to left.


Floating debris can give us an idea of speed and direction if we are stationary and this morning I looked for anything floating past to use the current to help me steer the boat away from the dock as we were leaving.  In this instance it pushed the bow of the boat off first.  We also watch other vessels around us to see if the current is pushing them sideways which we really care about when passing under bridges between abutments or are trying to avoid shallow water.


When we were tied to a mooring ball in heavy currents and winds, the boat was completely confused about which way to face.  Sometimes the mooring ball would be pushed back under the boat by the current and it was interesting to see which would win the boat direction competition.  Again, we could never tell.

With tides, we have to check our routes carefully in advance and co-ordinate particular points during the day with high tides.  "Hell Gate" is one where low tide is 2 feet.  Good name.  Throughout the day we hear radio calls for tow boats to pull unlucky boaters off of sandbars.  Sometimes it is the result of poor planning but in the ICW, sand shoals continually shift and charts are not always accurate.  The beauty of tides is that they do rise so usually just waiting will release the boat from the sand.

As beautiful as the ICW has been for us, we have to be on our toes and are tired at the end of our days. At the same time, the up-side to tides and currents is the "edge effect", where plants and animals live between two diverse ecosystems.  We see more birds at low tide picking the insects on the ground.  Alligators are found right on that edge of in-between water and land as they try to regulate their body temperature and hunt for food.  Jelly fish, urchins, and crabs are easier to see.  We like this kind of edge.


It's my turn to check the anchor.  I can feel the current shifting again.


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