NavList:

Lu wrote:

> Were you using the GPS's indication of CMG or bearing to a distant mark?
>
> Hopefully you've seen all the subsequent posts, but basically we've all
> said CMG is NOT a reliable instantaneous heading indicator, but bearing
> to a distant waypoint is (assuming you're pointing at it).

> Bill wrote:

>> Considering the GPS is looking at COG 3-4 ft above the waterline, and it is
>> moving quickly sidewise as well as forward, a fool's game as I read it.
>> (What the heck, if you want to increase a sailboat's speed, just have
>> someone run to the foredeck with a hand-held GPS ;-)

Sorry if I was hazy.  Used both bearings and course by GPS, the latter with
little to no success.

Middle session of my introduction to sailing talk, GPS vs compass.  Visual
aids of course. Canoeing analogy (a Rosetta Stone in the Midwest, we've all
done it).  Point the compass across a pond with no wind or current.  We'll
say due west of your position on the opposite shore. Pick a landmark and
paddle toward it.  The compass and GPS will agree on the course.

Now let's move to a fast-moving stream running north to south, 4 mph current
and your paddling speed is 4 mph. (A sneaky foundation to using force
vectors for apparent wind, current sailing and leeway later.) Pick out a
landmark due west on the opposite shore and try to paddle your canoe to it
without changing the west compass bearing.  You will hit the shore
downstream (south) of your landmark.  Why? How far south? (Some will
understand the cross ferry.)

Now take this GPS, point your nose west and walk sidewise to the south.
What does the GPS tell you about your direction of travel?  What does the
compass tell you about the direction of your nose?

Then the COG vs compass diatribe until they get it.

Included--at no extra charge, situational awareness--is an aerial view of
Michigan City and the breakwater near of the lighthouse (THE waypoint).  As
well as anecdotal cases where waypoint-to-waypoint GPS sailors tacking back
from the south shore after a trip to the gambling boats in Hammond, or a day
in Chicago, run into the breakwater with much greater frequency than they
did in the old DR days.  Plus a profound but fraudulent explanation as to
why.

Not exactly backing a twin screw mega-yacht into a tight slip in a cross
wind and opposing current, but what the heck.  When and if I learn to do
that on a regular basis, I'll be more than happy to share the information
;-)

Bill


--~--~---------~--~----~------------~-------~--~----~
To post to this group, send email to NavList@fer3.com
To , send email to NavList-@fer3.com
-~----------~----~----~----~------~----~------~--~---