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    Re: DR navigation in the recreatiional fleet: was Role of CN at s ea
    From: Derrick Young
    Date: 2004 Oct 13, 11:35 -0400

    You have very clearly stated the issue that most educators are faced with -
    the tools (such as GPS) are readily available and can be purchased/used by
    anyone.  For most folks, knowing current position as well as having some
    historical data would appear to be sufficient.  Most boaters never leave
    sight of land and are familiar with their immediate area.  They want
    confirmation of where they are, how far they have traveled, how fast, fuel
    consumption (though some don't understand why), and how to get back to their
    dock.  They ask "Why do they need to understand the basics of piloting
    (LOPs, DR plots, current/leeway, etc.)?
    
    I can only tell you what I do to answer this question - this may/may not
    work for you.
    
    I make sure that they are aware that a sextant, RDF, LORAN, RADAR,
    SONAR/depth finder and GPS are nothing more than tools of the trade for a
    competent navigator.  They allow you to determine and/or confirm your
    position by reference to external objects such as charted elements
    (piloting), stars/planets (CN), radio beacons (RDF/LORAN - electronic nav)
    and orbiting space junk (GPS - again electronic nav).
    
    Most folks forget (or get too wrapped up in the buttons and displays to
    remember) that GPS (and e-nav in general) provides current position (a fix)
    and the heading between the last updates - everything else it either
    remembers or computes.  It does not understand of what is between you and
    the target (destination).  If you stray off your pre-determined course (your
    DR plot) (effects of current/leeway), GPS will provide you a new heading to
    your intended target.  This begs the question, what lies between you and the
    target (reefs, sand/mud bars, dry land, swamp, etc.)?  GPS and other
    generally available e-nav products do not supply or act upon that
    information.  A number of my students have asked about/stated and/or argued,
    "my GPS has all of the charts of the area, so can I rely on that heading."
    I have yet to find a publicly available GPS that will automatically
    determine and add waypoints around charted objects.  Unless the student has
    done this, the heading that they see is from their current position to the
    target regardless of what is in the way.  This is not an issue when you are
    at sea, but it is an issue when you are closer to land, in a bay or river.
    
    In a GPS familiarization course, I start by talking about our local area and
    it's conditions.  We boat on a lower James River (Virginia), the port of
    Hampton Roads, the Chesapeake Bay and mid-Atlantic coast.  We have lots of
    commercial traffic, shoals, mud flats.  Where we are, the river is 1.5 miles
    wide, but most is only 6 inches deep at low tide (there is a 300 wide
    channel - but not necessarily in the middle of the river).  I put a local
    chart (12251) on the wall and have them pick starting and destination
    points.  Using a string and a couple of push pins, I show them what heading
    their GPS will show if that is all of the information that they have.
    Invariably, this has them boating across mud flats, dams, dry land and all
    of the other water hazards.
    
    From here, I go into understanding basic chart information (DATUM, chart
    projections, survey dates, scales, lat/long and updating), then how to
    locate a position on a chart.  Amazing how many cannot find their lat/long
    on a chart.  Then back to the GPS - they need to understand the quality of a
    fix, waypoints, routes and tracks.
    
    During the first couple of hours, I have been able to develop a basic
    understanding of piloting and chart work.  They are now ready to start
    learning how to use their GPS in conjunction with a chart.  Here I return to
    the question of what track do we follow from our launch point to where we
    want to destination (target).  This leads right into what heading to we use
    when we are off course and need to return to the track.
    
    I have found that most rec boaters do not use charts because they do not
    understand them.  They purchase a GPS because of all of the bells and
    whistles that are there.  For many, the GPS chart display is as close as
    they have been to a nautical chart.  This display gives them a false
    security because they have no idea as to when it was generated or last
    updated.
    
    When we have gotten this far, I spend time working through some of the
    different GPS units, showing the menus, options and buttons.  Hopefully,
    they have brought their GPS so that they can understand things on the unit
    that they are using.
    
    I cover as much as the students can handle and tailor each session for the
    folks that are there.  After all, a bass boater has different needs from the
    weekend cruiser.
    
    Don't know if I have answered your questions or not.  If I haven't, let me
    know.
    
    derrick
    
    
    

       
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