[alberg30] GPS mount

[Mr. Kelly McDaniel]

Anyone contemplating "throwing out" your compass, pit log or sextant
please contact me direct as I could definitely put these to practical
use.

Kelly _/)

Robert Kirk wrote:

>  From: Robert Kirk <kirk at neptune.gsfc.nasa.gov>
>
> At 01:50 PM 2/26/00 -0500, sandersm at aol.com wrote:
> >[...]
> >Does the DGPS unit provide reliable speed readings?  I must confess
> (having
> >undue confidence in my piloting and dead reckoning skills) that I was
> totally
> >uninterested in GPS until the yard told me what a help it would be as
> a
> >knotmeter.  I'm not interested in holing my hull for a knotmeter, but
> the
> >thought of having a way to measure speed and pinpoint location with
> one
> >no-hassle instrument does appeal to me.  Bob's remarks about GPS's
> >uselessness as a knotmeter lead me back to my original inclination to
> avoid
> >all electronics.  Unless, perhaps, the DGPS solves the problems Bob
> mentions.
> >  Does it?
>
>
> GPS is impressively accurate and reliable in speed measurement.
>
> GPS speed is calculated (by all the manufacturers, now, I believe)
> from the
> satellites' doppler and not by differentiating their positions. So, to
>
> first order, SA is not a factor in the speed calculation once you get
> underway with more than a knot or two of speed. There may be minor
> differences amongst the manufacturers in the implementation of the
> doppler
> algorithms and the degree of smoothing but the newer units are all
> very
> good. If  I remember, the older Magellans did a terrible job and used
> position differentiation, averaged over a selectable interval. But
> they've
> been superseded. Even my antediluvian Motorola uses doppler. (You
> know,
> like the cop's radar).The bottom line is that you can expect 1/10
> knot  absolute speed accuracy from a moving boat -  pretty good
> compared to
> the log.
>
> However, you might not want to throw away the old Pit Log yet. GPS
> gives  you speed over the ground, which is great for navigation, but
> if
> you're racing you might want to know speed through the water, too.
> Anfd
> you can use the two of them in combination to calculate the current
> set &
> drift with a simple maneuvering board. Also, the log is analog and so
> is
> superior in picking up the quick trends of minor sail adjustments
> which
> might disappear in the noise of any digital calculation from GPS if
> you're
> racing.
>
> Anyway, the GPS is revolutionary; you could throw away your  compass,
> pit
> log, & sextant.
>
> Cheers,
> Bob Kirk
> Isobar #181
>
>
>
> -----------------------------------------------------------------------
> -----------------------------------------------------------------------
>

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