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From: Bob Austin (no email)
Date: Tue Jul 01 2003 - 16:43:30 EDT
What will be interesting is to see if the corrections are applied. I have
contacted C Map. There are some inaccuracies (mostly shoreline--not nav
aids) in my area--and also mis identification of marinas and services. C
map claims that they will be updating the charts every 6 months --and have a
"club" (for $80 a year) you can join for the updates. Interestingly the C
map does have some of my private aids to Navigation which were Coast Guard
registered about 2 years ago and in the correct location.
I did find that NOAA / DMA was responsive in the past when I found a shoal
area in the Caribbean--and it appeared on the next chart series (apparently
a small sea mount--I spent several hours around it, getting several Sat Nav
fixes, as well as charting the extend and steepness)
Certainly the pencil dot is bigger--but alas, few folks use pencils in
today's world.
Take care,
Bob Austin Pensacola, FL
----- Original Message -----
From: "NavCom Digital/SeaTech Systems" <>
To: "'Bob Austin'" <>
Sent: Monday, June 30, 2003 8:58 PM
Subject: RE: Too WAAS or Not Too WAAS
> Bob,
>
> Thanks for your clarity on this issue. What good is a more accurate
> position if you can't plot it? When Selective Availability (SA) was
> tuned off, standard GPS exceeded the accuracy of a NOAA chart. A simple
> test is to mark your paper chart with a number two pencil. How wide is
> that mark? There is no difference in GPS plotting with an Electronic
> Charting System since the size of the ship icon is a function of the
> software. A GPS position is already more accurate than most navigators
> can plot on current charts.
>
> The new NOAA ENC vector charts will be more accurate and will improve
> the situation when they are approved next month.
>
> The WAAS issue is makes for great beer talk around the marina but has
> little to do with marine navigation unless you're nervously fishing for
> square grouper on a moonless night...
>
> Fair winds _/)Steven Bowden
>
> SeaTech Systems
> Computerized Navigation & Communication
> Sales: 800.444.2581 Support: 281.334.1174
> Fax: 281.334.3320 www.sea-tech.com
>
>
>
> -----Original Message-----
> From:
> [mailto:] On Behalf Of Bob
> Austin
> Sent: Monday, June 30, 2003 4:57 PM
> To: Michael Maurice
> Cc: 1trawler world
> Subject: TWL: Too WAAS or Not Too WAAS
>
>
> I am going to disagree with Mike on this one. He makes some good
> points. WAAS is being developed as an aviation project. It is optamized
> for line of site. The Corrections are a radio message from one of two
> Inmarsat satelites which are geostationary at the Equator and the WAAS
> system is for continental USA only. The Diff GPS using the Radio
> beacons in the 300 khz frequency range by the Coast Guard is optimized
> for coastal navigation and is fully functional all of the way to Alaska
> and in Hawaii. This system requires a separate reciever and antenna.
> WAAS uses the GPS reciever and antenna. I fail to see where satelites
> are blocked when WAAS is enabled. Mike may be experiencing problems in
> the Northern Latitudes (in fact we lost our satelite radio up his way a
> couple of times--a southern Satelite). However down in the South where I
> have compared both DGPS and WAAS they seem to be equally accurate and
> better than convential GPS alone. I have both WAAS and non WAAS chart
> plotters on my current boat. A boat I recently sold had DGPS and WAAS
> both on it. Set on the most sensatitive setting there is a greater
> circle of error on the non WAAS system. Satellite aquisition
> depends on the reciever more than WAAS on or off. The 300 khz DGPS
> system
> accuracy depends on how close you are to the reference point. This
> holds true for the WAAS system (25 reference points--not necessary
> coastal). Both systems correct for Ionosphere error, Satellite clock
> error, Orbit error, Tropsphere and multipath errors which are the
> primary errors in the civilian GPS--Military uses different frequencies
> and has superior accuracy without the WAAS or DGPS.
>
> The reciever is basically a radio reciever that takes the data messages
> and processes them into a position. The processor and reciever are
> working all of the time--thus I don't see any more battery draw (
> certainly we have plenty of power in our boats--the hand helds use 1500
> to 2000 milliamp hour battties--the hand held recievers run for 12 to 24
> hours--or use 100 milli amps an hour or less--pretty small draw--and
> most of that is for the LCD screen and if charting soft ware is
> present.).
>
> Since most of the modern recievers have WAAS built in--at no extra
> cost--go ahead and use it. Your position will be more accurate. If you
> are out of Continental U S or in the far North, turn off WAAS. If you
> want the same accuracy going to Alaska, get the DGPS reciever for an
> extra $300+. However plain GPS is more accurate than many of the
> charts on chart plotters....so don't worry about this degree of
> accuracy.
>
> Bob Austin
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