On Fri, 21 Jan 2005 20:08:04 GMT, Bruce in Alaska
wrote:

In article et,
otnmbrd wrote:

Jim Donohue wrote:



Why with professional luddites like you and your ilk I am required for
progress otn.

As stated, "you just don't get it". In truth, I'm a prolific user of
GPS, both the basic readout and connected to a chart plotter, making use
of all the information it supplies.
However, especially in the coastal waters I mainly traverse nowadays,
it's NEVER my sole source of position information and in fact, plotting
a GPS position isn't all that much quicker or necessarily as accurate as
a simple radar range and bearing, or eyeball fix.


The aside points out that the real amateur sailor with sufficient skill to
cross oceans uses GPS otn...and have a likely non working celestial
capability. It is in no way an excuse of any type...merely an observation
on how life actually is. You likely don't like it otn but you really don't
get a vote.

You use your survey as an EXCUSE for not learning or using celestial.
G By "non working" I assume you mean they have the ability but don't
use it. That's their choice, just like it's the choice of many ship
Masters making ocean crossings to require their people to occasionally
take celestial fixes and when in sight of land or radar range, to take
visual fixes as well as radar fixes and compare them to the GPS.
I also note that in another reply, you are still not comfortable using
radar for navigation.... that's too bad.... you're missing out on a
great tool.

otn


I would like to add a simple note here.

OTN talks about using Radar and the Mark One Eyeball to get position
fixes while navigating in coastal and inshore waters. Ok, that is common
practice, and has been for MANY years.

Now consider the accuracy of those fixes, as compared with the accuracy
of an Electronic Position Fixing Device.

Mark One Eyeball.... Taking a sight with binocs even over a compass card
will usually get a line within a degree or two, IF the guy is really
good at it or is using one of those old WWII TBT's... Ok, now figure
that your going to have to do that on at least two bearings, and better
yet, three or four. Ok, now you have to go plot those bearings on the
chart using the reverse bearing from the marker you sited on, and then
figuring in the time difference between the bearings, and the speed of
advance, of the vessel, and you don't get a REAL FIX, but an AREA of
FIX that IS "Orders of Magnitude" bigger than the REALTIME GPS Fix.

Radar..... Same thing here, except that your bearing will tend to be
better, depending on the Horozontal Beamwidth of the antenna, and the
distance, and area of the target which the bearing is to. Again, the
AREA of the FIX will be smaller for the radar because the time to get
the bearins, (two or more) will be shorter, but the plotting times and
the speed of advance will be the same. Again the Area of fix will
be "Orders of Magnitude" larger than the REALTIME GPS Fix.

GPS Fix..... even with out WAAS, this should be in the 30 foot centered
circle, and the speed of advance isn't even a problem due to the small
amount of advance in the one second cycle times of GPS Calulations.
The same can be said for LORAN-C with modern day Receivers, that have
builtin Lat/LONG Calculators, especially if the route has been run
before, and Know Anomalies in the TD's are already accounted for.

Now all the above really is mostly not a GIANT Issue at 7 - 12 Knots,
as there is always enough time to figure this all out. However, I defy
anyone to show me how anything but a Very GOOD GPS Based Navigation
System can be used on a Fast Ferry doing 35+ Knots inside Boston Harbour.
Speed KILLS, and the faster these guys go, the faster one of them is
going to run the rest of us over, because the navigator isn't watching
where he is going, because he is busy PLOTTING his position.

Explain to me why this isn't a problem......

The ferry service between Stockhom and Helsinki was dependent on GPS
with its own diferential setup back in the 1980s, years before the
USCG had differential beacons, never mind WAAS.

They were threading a lot of islands really fast in all visibilities,
including zero. And their schedules were much faster than before GPS.

Differential at that time was crucial for cancelling the effects of
SA. Of course, they could survey the route themselves and verify the
correspondence between GPS and chart.

And, their differential system would have alarmed immediately on any
GPS failure.


Rodney Myrvaagnes J36 Gjo/a

For your upscale SUV: Dingle-balls hand knit of natural Icelandic yarn