NavList:

Fred-
"The orientation of the GPS antenna doesn't affect the GPS readings."

That's not what I was referring to. If a GPS antenna is on the masthead (which
is the extreme case) as the boat yaws, pitches, and rolls, the antenna acts as a
lever arm and amplifies the motion, whipping the GPS around, and presenting it
with speeds and motions that "the boat" as a while does not have. It is *those*
motions, caused by the position of the antenna, not the orientation of it, which
present false data that the GPS needs to filter out. And, inevitably, it can't
filter them out both instantaneously and perfectly, so they corrupt the overall
picture to some extent.

i.e., boat is tied to the dock, but pitches. Antenna amplifies the motion, and
the GPS says "WHeee! We're moving at five knots!".

Which I'm sure you already knew. I didn't use the word "orientation". I would
expect that all data, including heading and bearing, could be corrupted by
motions. In this case a difference of 2-5 degrees is virtually nothing, it is
less than the closest most small craft helmsmen can hold, which is why I'd
dismiss it as meaningless--from that small craft point of view. Obviously not
the same for a larger ship and better helmsman.


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