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From: Walt Chudleigh <wchudleigh_at_sisna.com>
subject: [Paddlewise] GPS accuracy
Date: Mon, 15 May 2000 09:44:25 -0600
I was very glad to hear (via Paddlewise) that SA has been discontinued.    The
GPS speedometer function was basically worthless at kayaking speeds with SA
and I had given up even trying to use it.  It was also far enough off when
river running in canyons that I lost some confidence in it.  I did a little
experiment over the weekend to test the accuracy now.  I attached my Garmin 12
to the stem of my road bike and compared the speed and odometer functions with
those on my bike.  My bike computer is a fairly high end model and is very
accurate.  I was happy to see that the GPS was right on most of the time, even
at slow speeds in the 2-5 MPH range.  The GPS reacts a little slower than the
speedometer- i.e. when braking fast from 25 to 0 for a stop light, but usually
matched the speedometer when travelling at a consistent speed.  I also
determined that it does not round mileage up.  My bike computer registers in
100th's of a mile versus 10th's on the GPS.  The latter didn't register the
next tenth until it actaully reached it.  (I.e. 1.06 would not round up to
1.1).  The mileage calculations were dead on and the Track Back function
worked perfectly.  


Getting rid of SA may have been Clinton's greatest gift to kayakers,
backpackers, et al, who can now really use and rely on GPS technology.


Anyone else had similar or other results?





Walt Chudleigh


Park City, UT





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From: Nick Von Robison <n.v.rob_at_deltanet.com>
subject: Re: [Paddlewise] GPS accuracy
Date: Mon, 15 May 2000 17:37:40 -0700
> Getting rid of SA may have been Clinton's greatest gift to kayakers,
> backpackers, et al, who can now really use and rely on GPS technology.
>

Hi Walt and all,

I too am amazed at the better accuracy of my GPS now that SA is turned off, but at
the risk of pontificating, I don't think I would rely on it totally.  I'll stick
to chart and compass also and be pleasantly surprised if the convenience and
accuracy of GPS doesn't undergo some glitches when I most need it i.e.; sunspot
activity, software/hardware glitches, satellite malfunctions in the atomic clocks
on those birds which throw everything else akilter,  local terrorist activity
which cause the gov to reinstate it without notice, and so on.  Even the big ocean
going  tankers and freighters still have a mate come on board at noon, take a noon
sight by sextant, and reduce his sight with the tables.  Partly this is out of
tradition and keeping their hand in, but partly a "backup to backups" if their
electronics fail.  I'm not suggesting that a sextant would be a very useful piece
of kayaking gear, but a compass and chart of the trek be kept current along with
your GPS waypoints as a backup  Or vice versa, however you are inclined.

Will this be Mr. Clinton's greatest legacy........?

-Nick


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From: Christine Allison <sailnut_at_asan.com>
subject: Re: [Paddlewise] GPS accuracy
Date: Mon, 15 May 2000 21:30:34 -0400
I am a total novice when it comes to kayaking.  However I have many years
experience cruising Long Island Sound with a Loran receiver.

I think that to much attention is being paid to the ultimate accuracy of
GPS receivers.

It is very rare for visibility to get below a 1/4 mile and I have never seen
less then 1/8 mile.  1/8 mile is about 625 feet MUCH more then  the error in
Loran.  In navigating via compass I could ALWAYS see the way point before
the Loran indicated arrival.  Please remember that you will be lucky to stay
within 5 degrees of your rhomb line.  Practice paddling straight!  I find
that the best tactic is to follow the receivers bearing indication and keep
a sharp look out!

The lesson from this is that unless you are trying to find a submerged
object the accuracy of all present electronic aids is vastly in excess of
your realistic needs!

Richard Smith

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From: Allan and Joyce Singleton <alsjfs_at_voyager.co.nz>
subject: RE: [Paddlewise] GPS accuracy
Date: Tue, 16 May 2000 20:08:23 +1200
Richard Smith wrote:
>
>  It is very rare for visibility to get below a 1/4 mile and I
>  have never seen
>  less then 1/8 mile.  1/8 mile is about 625 feet

That may be true for the sea, but on local inland lakes here we can get
rather thick fog. The worst I have experienced was at work when trying to
find a buoy at a water quality sampling site. It was about 200 metres
offshore, we had a good bearing, but a hand held compass only, and did not
find it. Visibility was less than 25 metres.

On our double kayak we have a Silva 75 compass permanently mounted ahead of
the rear cockpit. If fog is threatening I set the compass course on the
outer ring (I have poor memory), then Joyce can concentrate on the limited
view ahead while I concentrate on maintaining the correct course. As there
is no wind during these conditions, and no current, it is possible to keep
to within plus or minus 2 degrees of the course. It is probably easier to
maintain a course with the long stable double in fog than it would be with
two singles.

We do have a GPS, but it has yet to appear on deck. Now that accuracy has
improved, that could happen once I get a suitable waterproof enclosure for
it.

Allan Singleton
Hamilton NZ




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From: Jerry Hawkins <jhawkins_at_cisco.com>
subject: RE: [Paddlewise] GPS accuracy
Date: Tue, 16 May 2000 10:44:56 -0700
>Richard Smith wrote:
>>  It is very rare for visibility to get below a 1/4 mile and I
>>  have never seen
>>  less then 1/8 mile.  1/8 mile is about 625 feet
 
There are plenty of uses where precise accuracy is called for.  Here in the South San Francisco Bay area, at high tide or half tide, the entire Bay is kayakable.  At low tide or especially at a minus tide, the entire 9 square miles reverts to a mudflat with only a few narrow channels that can be paddled.  The Bay is extremely cool when you are in these channels, as the birds come out and the sea life is concentrated into the remaining water.  The trouble is, without GPS, discerning the unmarked channels is not a simple matter.  The water can, and does (and has) left me high and dry because I was not quite exactly where I thought I was.  The penalty for such a mistake is a half hour or hour of sitting there waiting for water to return.

GPS makes a wonderful speedometer, if you are working on maintaining a pace.

GPS is great for making your way across an open bay, part of which is subject to significant currents, and other parts which are less so, and none of which is on the chart.

GPS is helpful when you are making your way through passages which aren't on any map, and have few if any identifying features, such as the canals and streams inside Bair Island or Greco Island in the Bay.

But, GPS is really not something to stake your safety on.  I've had one die due to corrosion; more than one "oops, the batteries are dead"; and one is in the shop for service after being dropped.  Safety and real navigation is what compasses and charts are for.  GPS is a very cool tool, used properly, and within its limits.

jerry.
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From: Nick Von Robison <n.v.rob_at_deltanet.com>
subject: Re: [Paddlewise] GPS accuracy
Date: Mon, 15 May 2000 20:17:40 -0700
Richard,

> I think that to much attention is being paid to the ultimate accuracy of
> GPS receivers.
>

I believe you missed my point in that eclectronic gadgets are not to be relied
on totally, and only at one's own risk.  A convenience yes, but not a
totalittlty.  Chaart, compass, and tide tables should back this up.

--Nick


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From: <AndyTKnapp_at_cs.com>
subject: Re: [Paddlewise] GPS accuracy
Date: Tue, 16 May 2000 02:00:47 EDT
In a message dated 5/15/2000 10:47:55 AM Central Daylight Time, 
wchudleigh_at_sisna.com writes:

>  I attached my Garmin 12
>  to the stem of my road bike and compared the speed and odometer functions

I also did a comparison of a Garmin 12XL with an accurate bicycle odometer on 
a tour last year (before SA ended). At that time, the GPS speeds kept within 
about a half-mile per hour (one kilometer) with the odometer at a steady 
pace, but it took about a speed of 8-9 mph for it to kick in accurately. I 
haven't had time this spring to try it again, though.

-Andy Knapp
Minneapolis
54 F (12 C) and raining.
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From: Christine Allison <sailnut_at_asan.com>
subject: Re: [Paddlewise] GPS accuracy
Date: Tue, 16 May 2000 09:15:35 -0400
Are you seriously proposing that a fix accuracy of 25 feet or so will/could
be a factor in a life or death situation?

For my amusement, using some freeware moving map software interfaced to my
old Garmin GPS-38, I laid out a route, uploaded it to the GPS and followed
it while paddeling last Sunday. The accuracy of the process was dazzling!
Could I have navigated as well with a compass and current  tables... sure.
My point is that we spend to much time with trivia and not enough with the
important things.

In my opinion the single most important thing(s) for ANYBODY involved with
small boats are to make dammed sure what kind of weather lies in the
immediate future and the state of the tides and currents.  Everybody should
carry AND USE some kind of radio which will receive the local marine
forecast!

>From bitter experience I learned to resist the urge to go if the weather
will be questionable (for the type of boat you are using.)  I finished read
Matt Booze's book describing kayaking disasters.  Ignoring or being ignorant
of impending bad weather is a thread which weaves through to many of the
incidents described.

Incidentally, your remarks about the Sound are totally correct.  I generally
navigated )with great success) with hand bearing compass and depth sounder.

Richard Smith

<It seems to me GPS accuracy is a lot more relevant
> when you are beyond the sight of land, or in an area where navigational
> markers and charts are not as well developed.>


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From: Sailboat Restorations, Inc. <sailboatrestorations_at_worldnet.att.net>
subject: Re: [Paddlewise] GPS accuracy
Date: Tue, 16 May 2000 08:50:55 -0700
This is all well and good as long as you're in a place like Long Island
Sound, where (a) you can always see land on both sides, (b) the channels and
landmarks are well-documented and unmistakeable, (c) the conditions are
rarely rough, and (d) a quick hail on the VHF will bring help in a matter of
minutes (or just wait and some redneck in a motor boat will run over you)
(BTW, I live on LIS).  It seems to me GPS accuracy is a lot more relevant
when you are beyond the sight of land, or in an area where navigational
markers and charts are not as well developed.
Mark L

> I am a total novice when it comes to kayaking.  However I have many years
> experience cruising Long Island Sound with a Loran receiver.
>
> I think that to much attention is being paid to the ultimate accuracy of
> GPS receivers.
>
> It is very rare for visibility to get below a 1/4 mile and I have never
seen
> less then 1/8 mile.  1/8 mile is about 625 feet MUCH more then  the error
in
> Loran.  In navigating via compass I could ALWAYS see the way point before
> the Loran indicated arrival.  Please remember that you will be lucky to
stay
> within 5 degrees of your rhomb line.  Practice paddling straight!  I find
> that the best tactic is to follow the receivers bearing indication and
keep
> a sharp look out!
>
> The lesson from this is that unless you are trying to find a submerged
> object the accuracy of all present electronic aids is vastly in excess of
> your realistic needs!
>
> Richard Smith



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