[Rhodes22-list] Magnetic or True? By a famous nautical author... Other th...

[Rory Orkin]

That is pretty much what I was trying to say in the previous go around on
this.. When you use a pure gps not a chart plotter , the gps only givs lat &
Lon and a heading.. That is where the magnetic vs true comes into play.
You are only using the gps for a fix. The compass is used to steer a
course.. With the charting gps you have a visual reference, not unlike using
a fixed point on land to steer to. The compass reading is relative to that
point and will adjust it self . 
    Dont forget drift and current are going to all come into play here. A
compass heading has to account for all of that also. The charting gps infers
all that as well by again pointing you to a fixed waypoint..
             I have had the full evolution of navigation starting in about
1964. I sometimes miss the chart and divider days of the paper chart. It
added a certain level of skill and situational awareness to sailing that is
perhaps missing with the chartplotters. But time moves on. I actually have
gone to an automatic transmission on my car as well. :-)  


Brad Haslett-2 wrote:
> 
> Dave,
> 
> Yup, that's about right.  It doesn't matter what electronic device you are
> using for guidance, if you are following an electronically generated
> lubber
> line you only need to steer relative to the track.  It doesn't matter what
> the variation is at your location or the deviation for your craft, or how
> the compass is marked.  It could be a Russian compass and marked in
> 'potatoes' - if it takes 10 potatoes to the left to hold course it takes
> 10
> potatoes to the left to hold course.  Now when the electronics go kaput,
> all
> bets are off.
> 
> Brad
> 
> On 4/10/07, DCLewis1 at aol.com <DCLewis1 at aol.com> wrote:
>>
>>
>> Bill and Ed,
>>
>> I don't think it matters much if I were to try to sail a true heading as
>> magnetic, my chart plotting GPS  would straighten me out  quickly.  With
>> a
>> chart
>> plotting GPS I enter  my destination/way points on the electronic charts
>> in
>> the GPS unit and  then  I  watch my track evolve in real time as I
>> sail.  Of
>> course, I always try to start on the right magnetic bearing, since I
>> steer
>> via
>> compass, but it's not critical at all.  If I'm not headed where I want
>> to  be
>> headed relative to my desired way point, the plot on my chart plotting
>> GPS
>> will tell me immediately and quantitatively.   I can look at the  track
>> display
>> that's automatically displayed (no transferring plot points)  and
>> instantly
>> know if my course is too high or low and with that crude info  I can make
>> a
>> steering adjustment, note the new reading on the compass,  and then hold
>> that new
>> compass reading.  I  never make the  calculation to go from degT to degM,
>> instead I just note I'm off  track and adapt.
>>
>> As to deviation and variance, I'm not sure it matters when   a compass is
>> used with a chart plotting GPS.  The compass becomes a  relative
>> instrument that
>> is used to hold a heading appropriate to keep on,  or near,  the desired
>> trip
>> track, that's it.  The numbers on the dial  are just a way to help you
>> keep a
>> heading - whatever that heading  really is, and that heading is
>> ultimately
>> determined by your chart plotting  GPS.  Making progress to the next way
>> point is
>> what's important, and you  can see that evolve (or not evolve) on the GPS
>> display.  Steering  accurately by compass, as per John Vigor, is now
>> besides the
>> point - I use  the compass to hold a bearing that will keep me on my
>> desired
>> track (or get me  back to my desired track) and that track is monitored
>> accurately in real time by  my chart plotting GPS.
>>
>> And all of the above is accomplished without keeping my head
>> down  navigating
>> via GPS because the chart plotting GPS unit does all of the  calculations
>> and
>> plotting.  All I have to do is glance at the display  to see that I'm on
>> track or off track and if I'm off track what I have to do to  get back on
>> track.
>> If I want to know quantitatively how far off-track I  am, speed, or
>> whatever,
>> I have to change the display page - but that's pretty  quick & simple.
>>
>> And with GPS I always know where I am (Lat/Lon) much better than the
>> paper-plotters.  I don't think there's any question about that.
>>
>> Of course we should always know how to fall back to paper and pencil, 
>> but
>> I
>> think that fall back is a long ways back.  I think a chart plotting  GPS
>> can
>> really be a very useful asset - and it can be an especially useful  asset
>> at
>> night or in inclement weather (low vs).
>>
>> Dave
>>
>>
>>
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>> http://www.aol.com.
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