Chart Thoughts

Here it is the middle of February.  Snickerdoodle has been in her winter slip and tarps since November.  I am in my upstairs office and daydreaming about sailing.  I started thinking about using nautical charts to find my way around unfamiliar waters..... and the dangers of over-confidence when using those charts.

There is so much information that it is easy to overlook something that might be important.  So, what are a couple of the really important things to look for when first putting the new chart down on the chart table to plot a course or pre-plan a weekend sail?

One of the first things is to check to see what system of measurement is being used on your chart to display the depth of the water (soundings).  There are lots of numbers all over the water portion of the chart that show the depth of the water essentially at low tide.  At high tide the water's depth is deeper than the number indicates.  In the United States we use a different measurement for soundings than just about anywhere else in the world.  In pretty much the rest of the world, the measurements for water depth is done in meters (Metric).  Not so in the U.S.  In the U.S. for fresh water the soundings are done in feet.  So the water depths for the chart for Pend Oreille Lake are stated in feet.
For salt water regions of the U.S. the water depth is done using Fathoms (6-foot units).  So the chart for Puget Sound shows water depths in Fathoms.  The sounding information is noted at the bottom of the chart and often at the top of the chart as well.  BTW - a Meter is roughly 39.5 inches.  I generally figure a Meter to be a long three feet.  Snickerdoodle draws 4 feet empty and about 4.5 feet loaded.

Another important indicator on the chart is the Compass Rose.  This is a double circle of numbers indicating the degrees counted around the compass from 0 (North) to 359 (one degree west of north).  East is 090; South is 180;  and West is 270. The reason there are two circles of numbers is that the outer circle represents the compass as it shows True or geographic North (the North Pole on a globe).  The 0 has a line through it and a star that indicate the True North direction to the geographic north pole.  The inner circle of numbers represents the magnetic compass that shows the direction to the magnetic north pole.  For most places on the earth, True North and magnetic north are not exactly the same.  The inner (magnetic) circle shows the 0 with a line and an arrow pointing to the magnetic north pole.  In the example above, the magnetic north pole is 19.45 degrees east of True North.
It is important to realize this and remember that your compass will correspond to the inner circle - - NOT the outer one.  You can imagine that if you plotted your course to your next waypoint using the outer circle to find the course and then followed your compass with that course.  You would be steering your boat in the wrong direction.  Let's say that you figured your new course to be 040 using the outer ring of numbers and then steered 040 using your compass as reference.  Your actual True course would be 059.45.  That could get you in real trouble.  So, be certain to remember to use the inner circle if you are going to actually sail by compass numbers.

Is it important to have a chart and know how to use it?  Well, yes.  Here is a photo that I shot one day on Lake Pend Oreille when there was truly limited visibility of a quarter mile or less.  My chart and compass were invaluable finding my way home to Bayview without hitting anything or anybody.